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EFFECTS OF RESOURCE LIMITATION ON A DETRITAL-BASED ECOSYSTEM.

Abstract. We examined the importance of terrestrial detrital inputs to secondary productivity of a headwater stream. Following a year of pretreatment studies on two headwater streams, we excluded terrestrial litter inputs (= treatment) to one stream while using the other as a reference. We excluded litter for 3 yr followed by 1 yr of small woody debris ([is less than or equal to] 10 cm diameter) removal and litter exclusion. Monthly benthic samples were collected from dominant mixed substrate (cobble, pebble, and sand-silt) as web as from moss-covered bedrock outcrop substrates. We used randomized intervention analysis (RIA) to test the null hypotheses that no change in abundance or biomass of functional feeding groups or specific taxa occurred in the treatment stream relative to the reference stream.

Benthic organic matter was significantly lower in mixed substrate habitats of the treatment stream; however, small woody debris did not show a significant reduction prior to manual removal during year 4. At the end of the treatment period, total benthic invertebrate abundance in mixed substrates in the treatment stream was less than one-tenth of that in the reference stream, and biomass in the treatment stream was one-sixth of that in the reference stream. Biomass and abundance of shredders, gatherers, total primary consumers, and predators displayed significant treatment effects (P [is less than] 0.012--0.00001, RIA) in the mixed substrate habitats during the 4-yr treatment. Only scraper and filterer functional groups failed to show differences between streams during the 4-yr treatment. Twenty of the 30 taxa comprising [is greater than] 90% of total secondary production displayed a significant decrease in abundance, biomass, or both, in the treatment stream relative to the reference stream (P [is less than] 0.05, RIA). Total secondary production in mixed substrate habitats declined to 22% of pretreatment values by the fourth year of treatment and is among the lowest reported for streams. Removal of small woody debris resulted in an additional 47-50% decrease in abundance, biomass, and production of the benthic fauna compared to the third year of litter exclusion.

In contrast, fauna of moss-covered bedrock substrates displayed no significant differences between streams in terms of any functional group, or in terms of abundance and biomass of individual taxa. Furthermore, secondary production on bedrock outcrops remained similar between streams. Results strongly suggest that food webs of bedrock habitats are not as closely linked to immediate allochthonous inputs from the surrounding forest as those of mixed substrates, although they may be linked in the long term.

Using a 9-yr record, we determined the relationship between organic matter standing crop and invertebrate abundance, biomass, and production in the treatment stream. There is a strong relationship between leaf litter standing crops and seedy productivity in mixed substrate habitats. In contrast, bedrock outcrop fauna showed a stronger relationship to fine benthic organic matter (FBOM) standing crop than to leaf litter. Despite a large residual mass of organic matter in the treatment stream, as well as other ongoing sources of input (dissolved organic matter, soil organic matter, and throughfall), litter exclusion clearly shows strong bottom-up effects extending from primary consumers to predators.

Abundance, biomass, and production of predators in the treatment stream were also strongly related to that of their prey throughout all pretreatment and treatment years. Our results suggest that, owing to simple bioenergetic efficiencies, production of predators is constrained by productivity of their prey. Although our results clearly show strong bottom-up effects, the importance of predators (top-down) can not be ignored, as available data suggest that predators consume most benthic invertebrate production. Our study underscores the importance of terrestrial-aquatic linkages in maintaining productivity of headwater streams draining forested catchments.

Key words: bottom-up regulation, benthos; detritus; food webs; functional groups; land-water interface; resource limitation; secondary production; stream; stream insects; top-down; woody debris.

INTRODUCTION

Detritus has been recognized as an important component of both terrestrial and aquatic systems (e.g., Odum and de la Cruz 1963). About 70 to 80% of all primary production from forest (O'Neill and Reichle 1980) and stream (Wetzel and Ward 1992) ecosystems eventually enters the detrital food web. In most streams draining forested headwater catchments in eastern North America, allochthonous inputs from the surrounding forest far exceed those of within-stream primary production (Webster et al. 1995). Furthermore, with the exception of tundra and arid land streams, allochthonous inputs to streams exceed those of autochthonous sources for most streams that have been studied (Webster and Meyer 1997).

Detritus is pervasive throughout most ecosystems, and many animal populations rely on it as a food resource. For example, soil invertebrate abundance and biomass display positive relationships with soil organic matter in agroecosystems (Hendrix et al. 1986, 1992, Roper and Gupta 1995) as well as in forests (Blair et al. 1994). Small plot manipulations of litter supplies to the forest floor also indicate an important linkage between organic matter and nematode populations (Arpin et al. 1995). Large pools of dissolved and particulate organic detritus may be much more important in lakes than generally acknowledged (Wetzel 1995). In some regions, high biomass of intertidal grazers and filter feeders is maintained by subsidies of detritus from offshore kelp beds (Bustamante et al. 1995, Bustamante and Branch 1996). Detritus and its infusion into many classic food webs are often-ignored but very important parts of food web complexity (Polls and Strong 1996, Polls et al. 1997). Furthermore, detrital subsidies from one habitat may contribute substantially to productivity of other habitats (Polls at el. 1997).

Since the first half of the 20th century, it has been known that many stream-dwelling invertebrates consume detritus of terrestrial origin (e.g., Lloyd 1921, Hynes 1941, Brinck 1949), and productivity of some invertebrate assemblages in some headwater streams relies on detrital inputs from the surrounding forest (Hynes 1963, Ross 1963). Thus, widely accepted linkages exist between detritivores, detritus, and detritus processing in streams (Fisher and Likens 1973, Cummins 1974, Hynes 1975, Anderson and Sedell 1979, Webster and Benfield 1986, Cushing et al. 1995, and Wallace and Webster 1996).

Detritivores held in artificial streamside channels were food limited (Richardson 1991), and higher levels of coarse particulate organic matter (CPOM) loading resulted in higher densities of collectors feeding on fine particulate organic matter (FPOM, Richardson and Neill 1991). Significant increases were observed only for pooled gatherers and filterers and not for individual taxa. Moderate, nonsignificant increases in predatory invertebrates were found in the high CPOM channels (Richardson and Neill 1991). In an ecosystem-level study, we excluded leaf litter inputs to a headwater stream for 3 yr and found significant decreases in abundance or biomass of CPOM- and FPOM-feeding detritivores as well as predators compared to populations in a nearby reference stream (Wallace et al. 1997). In this manipulation of detrital inputs we noted that, despite litter exclusion, a large residual mass of woody debris and FBOM remained in the treated stream.

Woody debris in streams influences a wide array of abiotic features as well as biotic community structure and function (Harmon et al. 1986). These include (1) rapid dissipation of stream energy in high-gradient systems (Heede 1972, Bilby and Likens 1980, Smith et al. 1993a, b), (2) reduced current velocities (Trotter 1990), (3) increased retention of particulate organic matter, which may also provide food for invertebrates (e.g., Bilby and Likens 1980, Speaker et al. 1984, Smock et al 1989, Trotter 1990, Wallace et al. 1995a), (4) substrate for invertebrates (Nilson and Larimore 1973, Benke et al. 1984, Smock et al. 1989), and (5) modification of stream habitat and benthic community structure (Molles 1982, Huryn and Wallace 1987a, Smock et al. 1989, Wallace et al. 1995a).

In addition to providing substrate and habitat, woody debris also provides food for some xylophagous invertebrates (Pereira et al. 1982) as well as enhances availability of FPOM by particle retention. During a 3-yr litter exclusion study, several invertebrate populations that showed no reductions in abundance or biomass represented taxa known to feed to some extent on woody debris or woody particles buried in the stream bed (Wallace et al. 1997). Epixylic biofilms--organic layers consisting of microbiota, extracellular polysacccharides, trapped FPOM, and dissolved organic materials--also represent a potential food resource for invertebrates (Couch and Meyer 1992, Tank and Webster 1998). Therefore, woody debris represents an additional terrestrial-aquatic linkage not directly addressed by Wallace et al. (1997) or other studies.

Many studies have examined the effects of adding resources such as nutrients to lakes (e.g., Schindler et al. 1978, Edmondson and Lehman 1981) and streams (Elwood et al. 1981, Peterson et al. 1985, Hart and Robinson 1990, Rosemond et al. 1993), or organic matter to streams (Warren et al. 1964). However, ecosystem-level studies that examine the effects of resource depression on stream invertebrate assemblages such as leaf litter reduction (Reice 1991, Richardson 1991, Wallace et al. 1997) or light reduction (Fuller et al. 1986, Steinman et al. 1990) are rare.

Most of the studies that examined the influence of resources on stream communities were conducted over relatively short time periods (weeks to [is less than] 1 yr) and examined changes in either abundance or biomass. Indirect effects associated with food limitation in detrital food webs probably require several generations of invertebrate consumers to detect significant changes (Richardson and Neill 1991). Multi-year manipulations of entire ecosystems are important tools to assess environmental change and the physical, chemical, and biotic factors controlling ecosystem-level processes (Carpenter et al. 1995). Therefore, experimental manipulation of terrestrial detrital inputs over multiple years represents an approach that allows assessment of terrestrial-aquatic linkages between allochthonous detritus and animal communities at the ecosystem level. However, few studies have examined the influence of resource manipulation on secondary production, which provides a better understanding of energy flow through the animal community than either abundance or biomass (e.g., Benke 1993).

In this paper, we report on a two-stage detritus manipulation that includes three years of leaf litter exclusion and a fourth year of litter exclusion combined with small woody debris removal. The objectives of this study were to assess the impact of this detritus manipulation on the following: (1) stream organic matter inputs and standing crops, (2) benthic animal abundance and biomass on two distinct types of substrates, and (3) secondary production, the flow (or flux) of mass [multiplied by] [area.sup.-1] [multiplied by] [time.sup.-1], which incorporates abundance, biomass, individual growth rates, survivorship, and development times into a single value (Benke 1993). Finally, we provide long-term data including 5 yr of pretreatment and 4 yr of treatment (3 yr of litter exclusion and 1 yr of litter exclusion combined with small woody debris removal) linking benthic productivity with inputs of organic matter from the surrounding forest. Our broad objective is to assess the effects of an ecosystem-level resource reduction on animal community structure.

STUDY SITES

The two streams examined in this study are within the Coweeta Hydrologic Laboratory (U.S. Forest Service) in western North Carolina. Coweeta is a 1625-ha drainage basin in the Blue Ridge Province of the southern Appalachian Mountains. Detailed descriptions of the Coweeta basin were given by Swank and Crossley (1988). The study streams are first order, and drain catchments (C) 53 (reference) and 55 (treatment). Vegetation consists of mixed hardwoods, dominated by oaks and hickories. Dense growths of understory rhododendron (Rhododendron maximum) result in heavy shading of the streams for most of the year. Elevation, area drained, thermal regime, discharge, and aspect (southern) are similar for the two streams (Table 1). Streams are fishless, and salamanders are the only vertebrates. Discharge was gauged continuously using FW-1 stage and ISCO 3230 Bubble Flow Meter (ISCO, Inc., Lincoln, Nebraska USA) recorders attached to 30-cm H-flumes at the base of each catchment.
TABLE 1. Physical parameters of streams draining catchments C 53
(reference) and C 55 (treatment = litter exclusion) at the Coweeta
Hydrologic Laboratory. Elevations were measured at the gauging
flumes.

              Variable                        C 53         C 55

Catchment
  Area (ha)                                   5.2          7.5
  Elevation (m asl)                         829          810

  Channel length (m)                        135          170
  Wetted width (m)([dagger])                  0.7-1.2      1.2-1.6
  Bankful channel area ([m.sup.2])          327          373
  Bedrock outcrop, % composition             27           13
  Mixed substrates, % composition            73           87

Discharge (L/s)
  Average (5-yr avg.)                         1.85         2.39
  Maximum (5-yr)                             34.0         40.2

Temperature (for 1985-1997, [degrees] C)
  Annual average (12-yr avg.)                12.2         12.2
  Annual degree-days (12-yr avg.)          4485         4512
  Maximum (12 yr)                            20.3         20.1
  Minimum (12 yr)                             0.7          0.7

Chemistry (1985-1993)
  pH                                         6.8           6.7
  [HCO.sub.3] (mg/L as Ca[CO.sub.3])         4.38          3.6
  [NO.sub.3]-N ([micro]g/L)                  3             4
  [NH.sub.4]-N ([micro]g/L)                  2             2
  SRP ([micro]g/L)                           3             2

([dagger]) Average wetted widths as measured during dry and wet
periods.


The substrate particle size distribution was assessed visually at 1-m intervals along the entire length of each stream (Table 1). In the two streams, 73% (reference) to 87% (treatment) of the substrate consisted of a heterogeneous mixture of cobbles, pebbles, gravel, sand, and silt, which we term mixed substrate habitat. The remaining substrate was composed of stretches of bedrock outcrop with growths of moss. The overall roughness of the stream bed topography, including woody debris, results in high retention, with abundant accumulations of leaves and wood. Cuffney et al. (1990) and Wallace et al. (1991) reported additional information about the study streams.

Precipitation during our study was usually above the long-term average of 182 cm/yr. When expressed as a percentage of the long-term average, year 1 (pretreatment) = 106%, year 2 = 124%, year 3 = 97%, year 4 = 111%, and year 5 = 114% (based on a 64-yr record from the Coweeta Hydrologic Laboratory data files).

METHODS

Benthic sampling

Invertebrates and benthic organic matter were sampled randomly by two methods (Lugthart and Wallace 1992). The mixed substrate habitats were sampled with a 400-[cm.sup.2] corer. Material within the corer was removed by hand and with a cup (to [approximately equal to] 10-cm depth or bedrock). After removal, water depths in the corer were measured for volume estimates, and following agitation, a subsample of the water in the corer was removed for later organic matter quantification using the methods described by Lugthart and Wallace (1992). Bedrock outcrops were sampled by scraping and brushing moss and associated particles from a 15 x 15 cm area into a plastic bag that was pressed to the rock surface. From September 1993 to August 1997 samples were collected monthly from each stream. Seven benthic samples, four from mixed substrates and three from bedrock outcrops, were collected from each stream on each sampling date.

Organic matter in samples, including invertebrates and salamanders, was elutriated from the inorganic substrate, passed through nested 1-mm and 250-[micro]m sieves, and preserved in a 6-8% formalin solution containing Phloxine B dye to facilitate sorting. Animals were removed from the CPOM on the 1-mm sieve by hand picking under 15x magnification and preserved in 6-8% formalin solution. CPOM and FBOM in the samples were processed, weighed, ashed, and re-weighed to obtain ash free dry mass (AFDM) of different categories following the procedures of Lugthart and Wallace (1992). Material on the 250-[micro]m sieve was subsampled (1/8-1/64 of the whole sample) using a sample splitter (Waters 1969) following Lugthart and Wallace (1992). Invertebrates in the subsample were removed by hand using a stereomicroscope (15x magnification). Invertebrates and larval salamanders were identified and counted. Identifications of insects were made to species or genus. Larval chironomids were identified as either Tanypodinae or non-Tanypodinae. Most non-insect invertebrates were identified to the ordinal level or higher. The body length of each individual was measured to the nearest mm using 12x magnification and a graduated stage or an ocular micrometer. We measured snout-vent lengths of salamanders. For Copepoda, Hydracarina, Nematoda, and Cladocera, biomass (AFDM) was obtained from mean mass of [is greater than] 50 individuals in subsamples of representative size classes. For other taxa, biomass was obtained using length-weight regressions derived from animals in the study streams, nearby Coweeta streams (Huryn 1986), or, for several taxa of Trichoptera, other North Carolina streams (Smock 1980).

Production

Annual production for most taxa was estimated using the size-frequency method (Hamilton 1969) and was corrected for the cohort production interval (CPI, Benke 1979). Invertebrate CPIs were the same as those used by Lugthart and Wallace (1992) and were estimated using length-frequency histograms constructed from monthly samples of each taxon in either the study streams or another Coweeta stream (Huryn and Wallace 1987a, b). For salamanders, we used larval development periods from Lugthart (1991).

Production of non-Tanypodinae chironomids was estimated using the community-level method of Huryn (1990). An empirically derived production/biomass (P/B) value of 18 for Copepoda (O'Doherty 1985) was assumed. The product of standing stock biomass and annual P/B ratio was used to estimate production for the remaining taxa. Theoretical P/B values of 5 and 10 were used for several taxa considered to be univoltine and bivoltine, respectively (Waters 1977, Lugthart and Wallace 1992). With the exception of oligochaetes, these taxa comprised a very small portion of total biomass. Oligochaete taxa were grouped, and voltinism was uncertain; thus production was estimated using a P/B value of 5. These estimates may be conservative, since higher reproductive rates have been reported for some oligochaetes (Brinkhurst and Cook 1980).

Production was estimated separately for the mixed substrate and bedrock outcrop substrate. Habitat-weighted production for the entire stream can be calculated using the proportion of bedrock outcrop and mixed substrates (Table 1).

Animals were assigned to the following functional feeding groups: shredder, collector-gatherer (= gatherers), scraper, collector-filterer (= filterers), or predator. Designations were made following Merritt and Cummins (1996) or based on our knowledge of the local fauna. Generally these followed those of Lugthart and Wallace (1992) and Whiles and Wallace (1995), the one exception being Stenonema sp. Extensive gut analysis of Stenonema specimens revealed little evidence of diatom feeding in these streams, and they were transferred from scrapers to collectors (S. L. Eggert, J. B. Wallace, and J. L. Meyer, unpublished data). For between-stream analysis of total primary consumers, we summed shredders, gatherers, scrapers, and filterers. For long-term (9 yr) measurements of production, we used previous measurements from 1985 and 1986 (Lugthart and Wallace 1992) and 1989 and 1990 (Whiles and Wallace 1995) from C 55. Stenonema sp. was reassigned as a gatherer group for these multi-year comparisons.

Functional feeding groups are based primarily on mode of feeding. This is not entirely satisfactory for filter-feeding hydropsychid caddis flies, which are omnivorous in these streams; a portion of their food is derived from animal consumption. For long-term comparison of predator-prey relationships, we assigned a portion of filterer abundance and biomass to predators (30% for Parapsyche cardis and 15% for Diplectrona spp.) based on the animal consumption values of these taxa in a nearby Coweeta stream (Ross and Wallace 1983). Our values for total primary consumers and predators differ slightly from those reported by Wallace et al. (1997) because they include another year of data and because filterers were recognized as omnivores.

Following a year of pretreatment study on C 55 and the reference stream (C 53), a litter exclusion canopy was constructed in August 1993 on C 55. The canopy, made from gill netting (1.2-cm mesh), was constructed over the bankful channel width and below the rhododendron understory to exclude falling leaves and small woody debris. Along each side of the 180-m canopy, we erected a fence 20 cm high to exclude blow-in and lateral movement of litter. The canopy was open at the sides to allow aerial insect colonization. Any accumulated leaf litter on the canopy was removed at regular intervals using a leaf blower. Light attenuation by the canopy is [is less than] 1%. In late summer 1996, following 3 yr of litter exclusion, we removed all small ([is less than or equal to] 10 cm diameter) woody debris on the stream bed surface by hand. All woody debris removed from the stream bed was measured (length and diameter) and subsampled to obtain mass per unit volume. Subsamples of known volume and surface area were also collected and preserved in formalin to assess invertebrate populations associated with removed wood. On 12 November 1996 and 10 April 1997 we removed small woody debris appearing on the stream bed, because buried wood surfaced during storm flows.

Pretreatment litterfall inputs were assessed from the period of winter 1985 through autumn 1988 using eighteen 0.25-[m.sup.2] traps placed every 10 m along or above each stream. Lateral litter inputs were estimated using 12 traps (0.5 m long) placed along the banks of each stream (Wallace et al. 1995b). Following canopy construction, direct litterfall was measured using the same type direct-fall traps inside (n = 16) and outside (n = 6) the canopy, as well as lateral movement traps inside (n = 16) and outside (n = 6) the lateral movement fence of C55. Concurrently, direct (n = 6) and lateral movement (n = 6) traps were placed along the reference stream (C 53). Collecting and processing litter inputs followed the procedure described by Wallace et al. (1995b).

This ecosystem-level study is unreplicated, employing one treatment and one reference stream. We used Randomized Intervention Analysis (RIA, Carpenter et al. 1989) for comparing before- and after-treatment changes in C 55 relative to C 53 for benthic detritus and abundance and biomass of specific animal taxa and functional feeding groups. RIA tests the null hypothesis that no change in the variable of interest occurred in the treatment stream relative to the reference stream following treatment. Rejection of the null hypothesis of no change, combined with divergent trends between reference and treatment following manipulation, implies a treatment effect.

RESULTS

Leaf litter inputs

Direct and lateral movement traps showed that leaf litter inputs to C 55 were reduced by 95% for direct leaf-fall and 94% for lateral movement by the exclusion canopy and lateral movement fence (Table 2). Direct leaf-fall into the treatment stream was 338 g AFDM [multiplied by] [m.sup.-2] [multiplied by] [yr.sup.-1] during pretreatment and outside the canopy during treatment, compared to 18 g [multiplied by] [m.sup.-2] [multiplied by] [yr.sup.-1] for traps under the canopy. Lateral movement declined from 293 g AFDM [multiplied by] linear [m.sup.-1] [multiplied by] [yr.sup.-1] outside the lateral movement fence to 18 g inside the fence. RIA indicated a significant difference in leaf-fall between the reference stream and measurements made under the canopy of the treatment stream (P = 0.021), but not outside the canopy (P = 0.271). Lateral movement measures indicated very significant differences in litter input between reference and treatment streams during the exclusion period (P [is less than] 0.0001), but no difference between streams outside the fence (P = 0.115).
TABLE 2. Direct leaf-fall (g AFDM [multiplied by] [m.sup.-2]
[multiplied by] [yr.sup.-1]) and lateral movement (= blow-in)
of leaves (g AFDM [multiplied by] linear [m.sup.-1]
[multiplied by] [yr.sup.-1]) for the reference stream (C 53)
and the treatment stream (C 55) during pretreatment and
treatment (litter exclusion) years.

Stream   Measurement                                n

C 53     Direct fall                                6
C 55     Direct fall([dagger])                      6
C 55     Direct fall (treatment)([double dagger])   3
C 53     Lateral movement                           6
C 55     Lateral movement([sections])               6
C 55     Lateral movement (treatment)([parallel])   3

Stream   Mean ([+ or -] SD)

C 53      387 ([+ or -] 25.1)
C 55      338 ([+ or -] 55.0)
C 55     18.0 ([+ or -] 11.1)
C 53      472 ([+ or -] 190.4)
C 55      293 ([+ or -] 103.1)
C 55     18.1 ([+ or -] 8.2)

Note: During treatment periods in C 55, direct litterfall and
lateral movement traps were located inside and outside the
exclusion canopy and the lateral movement fence.

([dagger]) Includes 3-yr pretreatment and 3 yr of measurement
outside exclusion canopy.

([double dagger]) Includes 3-yr of measurements made inside litter
exclusion canopy.

([sections]) Includes 3-yr of pretreatment and 3 yr of measurements
outside lateral movement fence.

([parallel]) Includes 3 yr of measurements made inside lateral
movement fence.


Organic matter standing crop

Benthic organic matter standing crop displayed significant changes between streams only in the mixed substrate habitats. Three categories of benthic organic matter (leaf detritus, fine benthic organic matter [FBOM], and total coarse benthic organic matter [CBOM]) showed significant between-stream differences during the litter exclusion and the small woody debris removal period (Table 3). Changes in leaf detritus and FBOM were highly significant between streams (P [is less than] 0.000001), whereas the change in CBOM was marginally significant (P = 0.010). Despite small woody debris removal during the fourth year of litter exclusion, the overall decrease in small woody debris throughout the period was not significantly different between streams (P = 0.709 for mixed substrates). However, following small wood removal, i.e., comparing only the fourth year of treatment (litter exclusion and small woody debris removal) with pretreatment, there was a significant difference in small woody debris between streams (P = 0.037, Table 3). In contrast to mixed substrates, moss and FBOM stored on bedrock substrates showed no significant difference between streams during the 4-yr treatment period (Table 3).
TABLE 3. Organic matter standing crops (g AFDM/[m.sup.2]) for
mixed substrate and bedrock outcrop habitats before treatment
(before) and following treatment (after = litter exclusion) of
C 55. C 53 is the reference stream.

                Habitat               C 53, before   C 55, before

Mixed substrates
  Total FBOM                             1081.2         772.5
  Total CBOM                             1057.9         704.7
  Leaf detritus                           149.4         111.1
  Small woody debris([dagger])            690.9         443.6
  Small woody debris([double dagger])     690.9         443.6

Bedrock outcrop
  Total FBOM                               16.0          14.8
  Total CBOM                               34.3          31.1
  Moss                                      9.2          14.7

                Habitat               C 53, after   C 55, after

Mixed substrates
  Total FBOM                            1535.8         584.7
  Total CBOM                            1387.2         527.6
  Leaf detritus                          258.9           7.1
  Small woody debris([dagger])           735.9         434.1
  Small woody debris([double dagger])    844.6         121.5

Bedrock outcrop
  Total FBOM                              19.9          18.0
  Total CBOM                              29.9          17.0
  Moss                                     9.8           9.6

                Habitat                   RIA probability       n

Mixed substrates
  Total FBOM                          <0.000001                 72
  Total CBOM                           0.010                    72
  Leaf detritus                       <0.000001                 72
  Small woody debris([dagger])         0.709([dagger])          72
  Small woody debris([double dagger])  0.037([double dagger])   36

Bedrock outcrop
  Total FBOM                           0.833                    60
  Total CBOM                           0.395                    60
  Moss                                 0.102                    60

Notes: Results of the RIA are based on monthly samples with
"before" data from 1984-1985 and 1992-1993 and "after" data from
September 1993 to August 1997. RIA tests the null hypothesis that
no change occurred for each type of organic matter in the
treatment stream (C 55) relative to the reference stream (C 53),
with n = total number of months included in test. Monthly data for
bedrock outcrop samples in 1984-1985 were not available.
CBOM = coarse benthic organic matter (> 1 mm), FBOM = fine benthic
organic matter (< 1 mm).

([dagger]) Includes entire litter exclusion period plus small wood
removal year for the treatment stream.

(double dagger]) Includes only last year (small woody debris
removal) for the treatment stream.


Temporal differences between streams in average benthic organic matter (BOM) standing crop were evident in mixed substrate habitats. Over the 4-yr period of litter exclusion, BOM declined in the litter exclusion stream and increased in the reference stream (Fig. 1 and Table 4). During the entire treatment period, BOM standing crop in mixed substrates of the exclusion stream declined at an average rate of 0.795 [+ or -] 0.336 g AFDM [multiplied by] [m.sup.2] [multiplied by] [d.sup.-1] (mean [+ or -] 95% CI, Table 4). This decline includes both CBOM and FBOM (0.517 [+ or -] 271, 0.278 [+ or -] 0.159 g AFDM [multiplied by] [m.sup.-2] [multiplied by] [d.sup.-1], respectively [mean [+ or -] 95% CI, Table 4]).

[Figure 1 ILLUSTRATION OMITTED]
TABLE 4. The top part of the table reports the coefficient of
determination ([r.sup.2]) between time (elapsed days, independent
variable) from start of litter exclusion in September 1993 and
monthly average standing crop of benthic organic matter
(g AFDM/[m.sup.2], dependent variable), including total benthic
organic matter (BOM), coarse benthic organic matter (CBOM), and
fine benthic organic matter (FBOM), in mixed substrate habitats
of the treatment stream (C 55, litter exclusion) and the reference
stream (C 53). The bottom part of the table gives the same
information for total invertebrate abundance (individuals/
[m.sup.2]) and invertebrate biomass (mg AFDM/[m.sup.2]).

   Stream                     Dependent variable        [r.sup.2]

Benthic organic matter
  C 53                   Total BOM                        0.059
  C 55                   Total BOM                        0.330
  C 53                   Total CBOM                       0.037
  C 55                   Total CBOM                       0.243
  C 53                   Total FBOM                       0.038
  C 55                   Total FBOM                       0.211

Invertebrates
  C 53                   Total invertebrate abundance     0.025
  C 55                   Total invertebrate abundance     0.400
  C 53                   Total invertebrate biomass       0.002
  C 55                   Total invertebrate biomass       0.333

                                              95%  CI
   Stream                  P       Slope     (for slope)

Benthic organic matter
  C 53                   >0.05      NS
  C 55                   <0.001    -0.795   [+ or -] 0.336
  C 53                   >0.1       NS
  C 55                   <0.001    -0.517   [+ or -] 0.271
  C 53                   >0.1       NS
  C 55                   <0.001    -0.278   [+ or -] 0.159

Invertebrates
  C 53                   >0.2       NS
  C 55                   <0.001   -17.55    [+ or -] 6.4
  C 53                   >0.5       NS
  C 55                   <0.001    -0.442   [+ or -] 0.19

Notes: P = significance level of regression; slope (coefficient)
has units of g AFDM [multiplied by] [m.sup.-2] [multiplied by]
[d.sup.-1] for organic matter, individuals [multiplied by]
[m.sup.-2] [multiplied by] [d.sup.-1] for invertebrate abundance,
and mg AFDM [multiplied by] [m.sup.2] [multiplied by] [d.sup.-1]
for invertebrate biomass. In each case, n = 48 and df = 46;
Ns = nonsignificant relationship.


Invertebrate response

Total invertebrate abundance in mixed substrate habitats of the treatment stream and reference stream displayed different trends during the treatment period. Invertebrate abundance decreased in the exclusion stream during the treatment period, while increasing in the reference stream, resulting in a very significant treatment effect between streams (P [is less than] 0.000001, RIA; Table 5). Invertebrate biomass in the mixed substrate habitats of the treatment stream at the end of the 4-yr treatment was 21% of the pretreatment year, while that of the reference stream exhibited little change ([is less than] 6%) between pretreatment and treatment periods (P [is less than] 0.001, RIA; Table 5).
TABLE 5. Average annual standing stock abundance and biomass of
total invertebrates in mixed substrates and moss-covered bedrock
substrates in the reference (C 53) and treatment (C 55) streams for
the pretreatment year, each of the three years of litter exclusion
(LE), and litter exclusion plus small woody debris removal
(year 4).

       Stream and substrate         Pretreatment   LE, yr 1

Abundance (individuals/[m.sup.2])
  C 53, mixed                          62 252       82 749
  C 55, mixed                          37 670       27 570
  C 53, bedrock                        20 477       15 642
  C 55, bedrock                        16 514         8537

Biomass (mg AFDM/[m.sup.2])
  C 53, mixed                           1 815        1 685
  C 55, mixed                           1 002          684
  C 53, bedrock                           870          384
  C 55, bedrock                           611          172

       Stream and substrate         LE, yr 2   LE, yr 3

Abundance (individuals/[m.sup.2])
  C 53, mixed                       106 361     93 949
  C 55, mixed                        21 800     16 663
  C 53, bedrock                      20 090     15 015
  C 55, bedrock                      15 507     22 079

Biomass (mg AFDM/[m.sup.2])
  C 53, mixed                         2 082      2 289
  C 55, mixed                           450        426
  C 53, bedrock                         478        589
  C 55, bedrock                         345        400

                                      LE + wood
       Stream and substrate         removal, yr 4   RIA probability

Abundance (individuals/[m.sup.2])
  C 53, mixed                          110 083
  C 55, mixed                            8 803         <0.000001
  C 53, bedrock                         13 869
  C 55, bedrock                         14 776          0.998

Biomass (mg AFDM/[m.sup.2])
  C 53, mixed                            1 707
  C 55, mixed                              212         <0.001
  C 53, bedrock                            518
  C 55, bedrock                            289          0.545

Note: Randomized intervention analyses (RIA) are probabilities of
no change (log[x + 1]-transformed data) in benthic abundance and
biomass between the reference and treatment streams for each of the
substrate types following treatment of C 55.


Total invertebrate abundance in the mixed substrates of the treatment stream decreased during each successive year (Table 5 and Appendix). The loss of invertebrates in mixed substrate habitats of the treatment stream was 17.5 [+ or -] 6.4 individuals [multiplied by] [m.sup.-2] [multiplied by] [d.sup.-1] (mean [+ or -] 95% CI) during the 4-yr treatment. Average invertebrate biomass loss during the treatment was 0.44 [+ or -] 0.19 mg AFDM [multiplied by] [m.sup.-2] [multiplied by] [d.sup.-1] (Table 4). Although overall abundance of invertebrates in mixed substrate habitats of the reference stream increased during the study, they displayed no distinct relationship with elapsed days, as did those of the treatment stream (Table 4).

In sharp contrast to mixed substrates, invertebrate abundance and biomass in moss-covered bedrock habitats exhibited little change between pretreatment and treatment periods. Average total abundance of invertebrates declined from the pretreatment to treatment period in bedrock habitats of both streams, i.e., by ~10% in the manipulated stream and 32% in the reference stream (P = 0.998, RIA, Table 5). Invertebrate biomass on bedrock outcrops also decreased, exhibiting a 53% decline during the treatment period in the treatment stream and a 40% decline in the reference stream (P = 0.545, RIA, Table 5). Furthermore, abundance and biomass of invertebrate populations on bedrock substrates tended to fluctuate in a similar manner over the 5 yr of the study (Table 5 and Appendix). Thus, invertebrate populations in moss-covered bedrock habitats in the two streams exhibited similar fluctuations throughout the 5-yr study, whereas those in mixed substrate habitats showed opposite trends.

Functional group changes

Abundance of shredders, gatherers, predators, and total primary consumers in mixed substrate habitats changed significantly after litter was excluded (P [is less than] 0.000001, RIA; Table 6). In the treatment stream, each of these four groups averaged a 47 to 51% decrease in abundance in mixed substrate habitats during the 4-yr treatment, compared to pretreatment values. Conversely, the abundance of shredders, gatherers, total primary consumers, and invertebrate predators increased in the reference stream during this same interval (Table 6 and Appendix). In addition to invertebrate predators, salamander abundance exhibited a significant treatment effect (P = 0.009, RIA). Annual values for most shredders, gatherers, predators, and total primary consumers tended to decrease in the treatment stream during each successive year (Appendix).
TABLE 6. Average abundance and standing stock biomass for
invertebrate functional feeding groups in mixed substrate habitats
of the reference (C 53) and treatment (C 55) streams during the
pretreatment period (before = September 1992 to August 1993) and
treatment period (leaf litter exclusion and small wood removal
[C 55], September 1993 to August 1997).

        Functional group            C 53, before   C 53, after

Abundance (individuals/[m.sup.2])

  Scrapers                                 44             23
  Shredders                             1 360          2 849
  Gatherers                            53 733         85 722
  Filterers                               288            402
  Total primary consumers              55 425         88 995
  Predators                             6 827          9 291

Biomass (mg AFDM/[m.sup.2])
  Scrapers                                  2              3
  Shredders                               700            726
  Gatherers                               339            283
  Filterers                               102             38
  Total primary consumers               1 143          1 050
  Predators                               672            891

        Functional group            C 55, before   C 55, after

Abundance (individuals/[m.sup.2])

  Scrapers                                562           387
  Shredders                               954           506
  Gatherers                            30 940        15 144
  Filterers                               323           176
  Total primary consumers              32 778        16 214
  Predators                             4 892         2 496

Biomass (mg AFDM/[m.sup.2])
  Scrapers                                  6             7
  Shredders                               401           187
  Gatherers                               158            63
  Filterers                                35            25
  Total primary consumers                 600           282
  Predators                               403           161

        Functional group            RIA probability

Abundance (individuals/[m.sup.2])

  Scrapers                              0.408
  Shredders                            <0.000001
  Gatherers                            <0.000001
  Filterers                             0.174
  Total primary consumers              <0.000001
  Predators                            <0.000001

Biomass (mg AFDM/[m.sup.2])
  Scrapers                              0.670
  Shredders                             0.012
  Gatherers                             0.001
  Filterers                             0.326
  Total primary consumers               0.006
  Predators                            <0.000001

Note: Randomized intervention analyses (RIA) are probabilities of
no change (log [x + 1 ]-transformed data) in benthic abundance and
biomass of each functional group between reference and treatment
stream following treatment of C 55.


Invertebrate predator (P [is less than] 0.000001, RIA) and gatherer (P [is less than] 0.001, RIA) biomass changed significantly following litter exclusion. Biomass of shredders (P [is less than] 0.012, RIA), total primary consumers (P [is less than] 0.006, RIA), and salamanders (P [is less than] 0.01, RIA) also decreased significantly following treatment. Although the increase in scrapers in the treatment stream was not significant (P = 0.670, RIA), this was the only functional group that did not show a decrease in biomass in mixed substrate habitats of the treatment stream following litter exclusion (Appendix).

In sharp contrast to mixed substrate habitats, no functional group displayed significant between-stream differences for either abundance (P = 0.22-0.863, RIA) or biomass (P = 0.39-0.994, RIA) in the bedrock outcrop substrates following litter exclusion and wood removal (Table 7). Salamanders also exhibited no change in bedrock outcrop habitats (P = 1.0 for abundance and P = 0.863 for salamander biomass). However, we caution that salamander abundance and biomass in bedrock habitats was very low and variable.
TABLE 7. Average abundance and standing stock biomass for
invertebrate functional feeding groups in bedrock outcrop habitats
of the reference (C 53) and treatment (C 55) streams during the
pretreatment period (before = September 1992 to August 1993) and
treatment period (litter exclusion and small wood removal [C 55],
September 1993 to August 1997).

        Functional group            C 53, before   C 53, after

Abundance (individuals/[m.sup.2])

  Scrapers                                174           266
  Shredders                               578           786
  Gatherers                            15 554        11 296
  Filterers                             1 127         1 125
  Total primary consumers              17 434        13 473
  Predators                             3 043         2 681

Biomass (mg AFDM/[m.sup.2])

  Scrapers                                 59            23
  Shredders                                82            64
  Gatherers                               186            92
  Filterers                               429           258
  Total primary consumers                 757           436
  Predators                               113            56

        Functional group            55, before   C 55, after

Abundance (individuals/[m.sup.2])

  Scrapers                               262          379
  Shredders                              622          520
  Gatherers                           12 191       11 631
  Filterers                              906          761
  Total primary consumers             13 982       13 290
  Predators                            2 532        1 934

Biomass (mg AFDM/[m.sup.2])

  Scrapers                                36           27
  Shredders                               52           35
  Gatherers                               90           61
  Filterers                              337          140
  Total primary consumers                514          263
  Predators                               97           38

        Functional group            RIA probability

Abundance (individuals/[m.sup.2])

  Scrapers                               0.782
  Shredders                              0.400
  Gatherers                              0.752
  Filterers                              0.227
  Total primary consumers                0.863
  Predators                              0.317

Biomass (mg AFDM/[m.sup.2])

  Scrapers                               0.822
  Shredders                              0.574
  Gatherers                              0.994
  Filterers                              0.916
  Total primary consumers                0.612
  Predators                              0.686

Note: Randomized intervention analyses (RIA) are probabilities of
no change (log[x + 1]-transformed data) in benthic abundance and
biomass for each functional group between reference and treatment
stream.


Individual taxa

At least 18 of the major taxa, which contributed [is greater than] 90% of total benthic production in mixed substrates, had either reduced abundance, biomass, or both, in the treatment relative to the reference (Table 8). Among the shredders displaying significant changes were plecopterans (Peltoperlidae and Leuctra spp.) and trichopterans (Lepidostoma spp. and Pycnopsyche spp.). One trichopteran shredder (Fattigia pele) exhibited no significant change following treatment. Although no dipteran shredders exhibited significant changes, three taxa of Tipulidae, Tipula spp., Molophilus sp., and Lipsothrix sp., approached significance (P [is less than] 0.10) in either abundance or biomass (Table 8). When only the fourth year of treatment (wood removal and litter exclusion) was compared with pretreatment, there was a significant difference (RIA) between streams for abundance (P = 0.013) and biomass (P = 0.04) of Tipula and Molophilus (P = 0.024). However, Lipsothrix biomass did not differ significantly between streams for pretreatment and fourth year of treatment (P = 0.069). Among gatherer taxa, the decrease in abundance of copepods and chironomids were especially striking, declining 78% and 57%, respectively, between pretreatment and the third year of litter exclusion. Following small wood removal, copepods and chironomids declined by 95% and 76%, respectively, of pretreatment values. The wood-associated larvae of Sciaridae (Diptera) showed a significant decrease in the treatment stream (P = 0.004 for abundance and 0.006 for biomass, RIA) when only the fourth year of treatment was compared with pretreatment. Three taxa, Neophylax sp, a scraper; Seratella sp., a gatherer; and Diplectrona modesta, a filterer, increased significantly in the mixed substrate habitat of the treatment stream relative to the reference stream (Table 8).
TABLE 8. Randomized intervention analysis of probability of no
change in abundance and biomass of functional groups and
specific taxa between the reference stream and the treatment
stream for four years of litter exclusion and including one year
of small woody debris removal.

       Functional group              Probability,   Probability,
           and taxon         Order    abundance       biomass

Scrapers
  Epeorus sp.                 E        0.409          0.528
  Baetis sp.                  E        0.428          0.213
  Ectopria sp.                C        0.859          0.785
  Neophylax sp.               T       <0.000001       0.015

Shredders
  Peltoperlidae               P        0.089          0.003
  Leuctra spp.                P        0.011          0.001
  Lepidostoma spp.            T       <0.000001      <0.000001
  Pycnopsyche spp.            T        0.004          0.003
  Fattigia pele               T        0.266          0.160
  Tipula spp.                 D        0.069          0.422
  Molophilus spp.             D        0.222          0.060
  Lipsothrix sp.              D        0.934          0.062

Gatherers
  Nematoda                    NI       0.018          0.059
  Oligochaeta                 NI     .17              0.816
  Copepoda                    NI      <0.000001      <0.000001
  Paraleptophlebia sp.        E        0.217          0.494
  Stenonema spp.([dagger])    E       <0.000001      <0.000001
  Seratella sp.               E        0.010          0.137
  Lype diversa                T        0.972          0.988
  Sciaridae (Bradysia sp.)    D        0.175          0.179
  Chironomidae([double
    dagger])                  D        0.001         <0.000001

Filterers
  Diplectrona modesta         T        0.022          0.116
  Parapsyche cardis           T        0.516          0.126

Invertebrate predators

  Lanthus sp.                 O       <0.000001       0.001
  Cordulegaster sp.           O       <0.000001       0.004
  Beloneuria sp.              P        0.006          0.004
  Isoperla spp.               P        0.516          0.244
  Sweltsa lateralis           P        0.542          0.393
  Rhyacophila spp.            T        0.982          0.021
  Pseudogoera sp.             T        0.414          0.701
  Tanypodinae                 D       <0.000001      <0.000001
  Ceratopogoniidae            D       <0.000001       0.001
  Hexatoma spp.               D       <0.000001      <0.000001
  Dicranota spp.              D        0.212          0.872
  Pedicia sp.                 D        0.064          0.100
  Empididae                   D        0.262          0.486

Vertebrate predators
  Salamanders                          0.009          0.010

       Functional group              Probability,   Probability,
           and taxon         Order    abundance       biomass

Scrapers
  Epeorus sp.                 E         0.142          0.085
  Baetis sp.                  E         0.017          0.221
  Ectopria sp.                C         0.487          0.063
  Neophylax sp.               T         0.344          0.042

Shredders
  Peltoperlidae               P         0.816          0.762
  Leuctra spp.                P         0.118          0.191
  Lepidostoma spp.            T         0.359          0.424
  Pycnopsyche spp.            T         0.214          0.125
  Fattigia pele               T         1.000          0.976
  Tipula spp.                 D         0.769          0.781
  Molophilus spp.             D         1.000          1.000
  Lipsothrix sp.              D         1.000          0.823

Gatherers
  Nematoda                    NI        0.938          0.682
  Oligochaeta                 NI        0.514          0.089
  Copepoda                    NI        0.992          0.616
  Paraleptophlebia sp.        E         0.481          0.577
  Stenonema spp.([dagger])    E         0.028          0.280
  Seratella sp.               E         0.822          0.250
  Lype diversa                T         0.558          0.844
  Sciaridae (Bradysia sp.)    D         0.752          0.703
  Chironomidae([double
    dagger])                  D         0.601          0.610

Filterers
  Diplectrona modesta         T         0.434          0.163
  Parapsyche cardis           T         0.827          0.911

Invertebrate predators

  Lanthus sp.                 O         0.922          0.755
  Cordulegaster sp.           O
  Beloneuria sp.              P         0.309          0.968
  Isoperla spp.               P         0.472          0.194
  Sweltsa lateralis           P         0.264          1.000
  Rhyacophila spp.            T         0.246          0.413
  Pseudogoera sp.             T         0.212          0.025
  Tanypodinae                 D         0.186          0.084
  Ceratopogoniidae            D         0.954          0.186
  Hexatoma spp.               D         0.646          0.788
  Dicranota spp.              D         0.090          0.285
  Pedicia sp.                 D         0.136          0.489
  Empididae                   D         0.805          0.771

Vertebrate predators
  Salamanders                           1.000          0.863

Notes: All analyses were run on log (x + 1)-transformed data based
on monthly means from both mixed substrate and bedrock habitats
(n = 60 for each habitat). Insect orders as follows: D = Diptera,
E = Ephemeroptera, NI = Noninsect, O = Odonata, P = Plecoptera, and
T = Trichoptera. Bold type denotes those taxa whose abundance or
biomass increased in a particular habitat in the treatment stream
relative to the reference stream. All other significant changes
were decreases in the treatment stream.

([dagger]) Functional feeding group based on absence of significant
diatoms in gut content analysis.

([double dagger]) Non-Tanypodinae Chironomidae.


Invertebrate predators in four orders exhibited a change between streams in mixed substrate habitats following treatment. These changes include decreases in abundance and biomass of two odonates, Lanthus sp. and Cordulegaster sp. The perlid stonefly, Beloneuria sp., decreased in biomass in the treatment stream by 95% in this period. Dipteran predators were also affected, with abundance declining by 6-81% for Ceratopogonidae, Tanypodinae, and Hexatoma spp. in mixed substrate habitats of the treatment stream (Table 8 and Appendix.).

Functional group production

By the fourth year of resource reduction, total secondary production in mixed substrate habitats of the treatment stream had declined by 78% from pretreatment values (5.01 g vs. 1.1 g AFDM [multiplied by] [m.sup.-2] [multiplied by] [yr.sup.-1]), while increasing by 6% in the reference stream (9.28 vs. 9.91 g AFDM [multiplied by] [m.sup.-2] [multiplied by] [yr.sup.-1]; Table 9). The decrease in production in the litter exclusion stream was more pronounced for predators than gatherers, gatherers than shredders, and shredders than filterers. However, one functional group, scrapers, displayed an average yearly increase of ~13% in production from the pretreatment year in the mixed substrate habitats of the treatment stream (Table 9 and Appendix.). Total secondary production of invertebrates declined during each successive year of treatment in the mixed substrate habitat of the treatment stream. In contrast, that of the reference stream increased somewhat during the same period (Table 9).
TABLE 9. Annual secondary production (mg AFDM [multiplied by]
[m.sup.-2] [multiplied by] [yr.sup.-1]) of invertebrates by
functional feeding group in mixed substrate and bedrock habitats
of the reference (C 53) and treatment (C 55) streams.

Functional group   Stream   Year 1   Year 2   Year 3

Mixed substrates
  Scrapers          C 53        13       16       10
                    C 55        33       35       26
  Shredders         C 53     3 851    3 625    3 646
                    C 55     1 810    1 718      545
  Gatherers         C 53     2 586    2 524    3 114
                    C 55     1 356      760      835
  Filterers         C 53       473      171      268
                    C 55       256      133      118
  Predators         C 53     2 357    3 106    3 661
                    C 55     1 629    1 237      630
  Sum               C 53     9 280    9 442   10 699
                    C 55     5 014    3 884    2 154
Bedrock outcrop
Scrapers            C 53       202       54      142
                    C 55       137       32       45
Shredders           C 53       387      512      411
                    C 55       412      382      190
Gatherers           C 53     1 520      799    1 258
                    C 55       918      378      865
Filterers           C 53     3 704    1 099    1 414
                    C 55     3 202      404      957
Predators           C 53       722      382      363
                    C 55       446      136      202
Sum                 C 53     6 535    2 846    3 588
                    C 55     5 115    1 332    2 259

Functional group   Stream   Year 4   Year 5

Mixed substrates
  Scrapers          C 53         2       24
                    C 55        51       37
  Shredders         C 53     5 443    2 774
                    C 55     1 003      242
  Gatherers         C 53     2 908    4 302
                    C 55       619      327
  Filterers         C 53       209      173
                    C 55       173      112
  Predators         C 53     4 706    2 639
                    C 55       279      386
  Sum               C 53    13 267    9 912
                    C 55     2 125    1 104
Bedrock outcrop
Scrapers            C 53       110      193
                    C 55       213      176
Shredders           C 53       637      218
                    C 55       420      144
Gatherers           C 53       839      849
                    C 55       934      805
Filterers           C 53     2 211    2 399
                    C 55     1 265    1 552
Predators           C 53       367      284
                    C 55       362      149
Sum                 C 53     4 163    3 943
                    C 55     3 193    2 826

Note: Year 1 is the pretreatment year (September 1992-August 1993)
for C 55, years 2-4 (September 1993-August 1997) are the years of
litter exclusion, and year 5 is the year of litter exclusion and
small woody debris removal for C 55.


In distinct contrast to mixed substrates, total secondary production of invertebrates in bedrock habitats of both streams fluctuated in a similar pattern during each year of the study (Table 9). Except for scrapers, each functional feeding group displayed similar fluctuations or reductions in bedrock outcrops of the reference stream during this same period (Table 9). As observed for mixed substrate habitats, scraper production in bedrock outcrops during the last two years of treatment of the treatment stream was higher than that of the pretreatment year.

Temporal trends in invertebrate populations

Trends in total primary consumer, invertebrate predator, gatherer, and shredder abundance or biomass in mixed substrate habitats of the reference and litter-excluded stream over the 1825-d study are shown in Fig. 2. Each of these groups decreased significantly through time in the litter-exclusion stream relative to the reference stream. Plots of monthly abundance indicate that the significant between-stream difference was due to a slight increase in the reference stream during years 2 through 5 and a consistent decrease in the treatment stream (Fig. 2). Annual cycles of abundance (peaks in autumn/winter of each year) were evident in the treatment stream even following litter exclusion, but total numbers of individuals declined each successive year. The increased downward trends in abundance and biomass following removal of small woody debris (-day 1460, in Fig. 2) are evident for most groups.

[Figure 2 ILLUSTRATION OMITTED]

Invertebrates in bedrock outcrop habitats showed very different patterns from those of mixed substrate habitats. Primary consumer and predator populations in the moss-covered bedrock habitat showed similar monthly trends in both streams, with abundance and biomass declining during year 2 of the study and increasing to year I levels during the final two years (Fig. 3).

[Figure 3 ILLUSTRATION OMITTED]

Additive effects of wood removal

The additive effects of wood removal were examined using RIA comparisons between streams for abundance and biomass of each functional feeding group for the last year of exclusion along with that of litter exclusion plus small woody debris removal. Invertebrate biomass of functional groups of shredders, gatherers, and total primary consumers differed significantly between streams for the mixed substrates (RIA, P [is less than] 0.05, Table 10). However, biomass did not differ significantly between streams for bedrock substrates following small wood removal. Comparison of abundance of invertebrates between these two periods revealed no significant differences between streams for any functional group in either mixed substrate or bedrock substrate (RIA, P [is greater than] 0.05, Table 10).
TABLE 10. Randomized intervention analysis testing the null
hypothesis of no change in abundance and biomass of each
functional feeding group between the reference and treatment
stream between year 3 (litter exclusion) and year 4
(litter exclusion plus small woody debris removal).

                              Mixed         Bedrock
                           substrates      substrates

     Functional or        Abun-   Bio-    Abun-   Bio-
     trophic group        dance   mass    dance   mass

Scrapers                  0.109   0.066   0.969   0.671
Shredders                 0.626   0.027   0.794   0.562
Gatherers                 0.154   0.022   0.668   0.455
Filterers                 0.998   0.120   0.276   0.618
Total primary consumers   0.172   0.012   0.874   0.946
Invertebrate predators    0.230   0.976   0.183   0.432
Salamanders               0.272   0.223   0.859   0.954

Notes: All analyses were run on log(x + 1)-transformed
data based on monthly means from both mixed substrate and
bedrock habitats (n = 24 for each habitat). See Appendix for
average abundance and biomass for each habitat.


Relationships between primary consumers and predators

Is there any evidence that predator abundance and biomass track that of their prey, and do similar relationships exist for the treatment and reference stream? During the 5-yr period, monthly benthic samples displayed a significant positive relationship between predator and primary consumer abundance and in some cases also biomass. For example, in mixed substrate habitats of both reference and treatment streams, there were significant relationships between monthly (n = 60) abundance of predators and that of primary consumers (reference stream, [r.sup.2] = 0.545, P [is less than] 0.001; treatment stream, [r.sup.2] = 0.728, P [is less than] 0.001; Table 11). The mixed substrates of the treatment stream also displayed a significant relationship ([r.sup.2] = 0.292, P [is less than] 0.001) between predator and primary consumer biomass, whereas the reference did not (Table 11). Gatherers constitute the most important component of the prey items in guts of predators, and predator abundance and biomass were generally positively related to that of gatherers (Table 11).
TABLE 11. Relationship between benthic abundance and biomass for
primary consumers or gatherers alone (independent variable) and
invertebrate predator abundance and biomass (dependent variable).

 Stream              Independent variable

Mixed substrate
  C 53               Primary consumer abundance
  C 55               Primary consumer abundance
  C 53               Primary consumer biomass
  C 55               Primary consumer biomass
  C 53               Gatherer abundance
  C 55               Gatherer abundance
  C 53               Gatherer biomass
  C 55               Gatherer biomass
Bedrock substrates
  C 53               Primary consumer abundance
  C 55               Primary consumer abundance
  C 53               Primary consumer biomass
  C 55               Primary consumer biomass
  C 53               Gatherer abundance
  C 55               Gatherer abundance
  C 53               Gatherer biomass
  C 55               Gatherer biomass

 Stream              Dependent variable

Mixed substrate
  C 53               Predator abundance
  C 55               Predator abundance
  C 53               Predator biomass
  C 55               Predator biomass
  C 53               Predator abundance
  C 55               Predator abundance
  C 53               Predator biomass
  C 55               Predator biomass
Bedrock substrates
  C 53               Predator abundance
  C 55               Predator abundance
  C 53               Predator biomass
  C 55               Predator biomass
  C 53               Predator abundance
  C 55               Predator abundance
  C 53               Predator biomass
  C 55               Predator biomass

                                             95% CI
 Stream              [r.sup.2]   Slope    (for slope)

Mixed substrate
  C 53                 0.545     0.577   [+ or -] 0.138
  C 55                 0.728     0.817   [+ or -] 0.131
  C 53                 0.031      NS
  C 55                 0.292     0.564   [+ or -] 0.231
  C 53                 0.532     0.555   [+ or -] 0.137
  C 55                 0.711     0.781   [+ or -] 0.131
  C 53                 0.042      NS
  C 55                 0.296     0.676   [+ or -] 0.274
Bedrock substrates
  C 53                 0.560     0.809   [+ or -] 0.189
  C 55                 0.681     0.740   [+ or -] 0.133
  C 53                 0.630     0.861   [+ or -] 0.173
  C 55                 0.649     1.147   [+ or -] 0.222
  C 53                 0.477     0.681   [+ or -] 0.188
  C 55                 0.642     0.636   [+ or -] 0.125
  C 53                 0.151     0.315   [+ or -] 0.196
  C 55                 0.226     0.514   [+ or -] 0.250

Notes: Regressions were based on [log.sub.10]-transformed monthly
means for abundance (individuals/[m.sup.2]) or biomass
(mg AFDM/[m.sup.2]) for mixed substrate and bedrock substrate
(n = 60 for each comparison). C 53 is the reference stream, and
C 55 is the treatment (litter exclusion) stream; NS = not
significant.


In bedrock outcrop habitats of both streams, there was a significant relationship between predator and primary consumer abundance and biomass. Predator abundance in monthly (n = 60) bedrock samples was strongly related to that of primary consumer abundance in both streams (reference stream, [r.sup.2] = 0.56, P [is less than] 0.001; treatment stream, [r.sup.2] = 0.68, P [is less than] 0.001). Predator biomass and primary consumer biomass on bedrock outcrop substrates were also strongly related (reference stream, [r.sup.2] = 0.63, P [is less than] 0.001; treatment stream, [r.sup.2] = 0.649, P [is less than] 0.001; Table 11). However, predator biomass in bedrock habitats of both streams was not as strongly related to gatherer biomass as was predator and gatherer abundance (Table 11).

Long-term relationships between resources and primary and secondary consumers

The five years of pretreatment studies of C 55 encompassed extreme drought and wet periods at Coweeta. During these five years, there were vast differences in leaf litter standing crop among years. Quite apart from the timing of storms, there was a significant negative relationship between maximum annual instantaneous discharge and annual average leaf litter standing crop (Fig. 4A).

[Figure 4 ILLUSTRATION OMITTED]

Annual invertebrate abundance, biomass, and production data in mixed substrate habitats from 1985 and 1986 (Lugthart and Wallace 1992), 1989, and 1990 (Whiles and Wallace 1995), and the current study were plotted with standing crop of leaf litter for each year. Over nine years of study, there was a strong positive relationship between leaf litter standing crop in mixed substrates and primary consumer abundance as well as predator abundance (Table 12, Fig. 4B). There were also very significant relationships between annual leaf litter standing crop and secondary production of shredders, collectors, total primary consumers, predators, and total invertebrates (Table 12, Fig. 4C) in mixed substrates over the 9-yr period. Only filterer and scraper functional groups showed no relationship between secondary production and standing crop of leaf litter for the mixed substrates (Table 12). Neither abundance, biomass, nor production of invertebrates in mixed substrate habitats displayed a significant relationship with annual FBOM standing crop in mixed substrates over the 9-yr period (Table 12).
TABLE 12. Long-term relationships between annual leaf litter
standing crop (g AFDM/[m.sup.2]) and fine benthic organic matter
(FBOM; g AFDM/[m.sup.2]) in mixed substrates and annual mean
abundance, mean biomass, and production of invertebrates in
C 55 for the years 1985, 1986, 1989, 1990, and September 1992 to
August 1997.

                                  Abundance          Biomass

 Functional feeding group    [r.sup.2]     P     [r.sup.2]     P

Leaf litter standing crop
  Scrapers                     0.423     NS        0.005     NS
  Shredders                    0.922     (***)     0.722     (*)
  Collectors                   0.875     (***)     0.836     (***)
  Filterers                    0.433     NS        0.475     (*)
  Total primary consumers      0.875     (***)     0.754     (*)
  Predators                    0.844     (***)     0.884     (***)
  Total invertebrates          0.875     (***)     0.874     (***)

FBOM standing crop
  Scrapers                     0.170     NS        0.315     NS
  Shredders                    0.001     NS        0.004     NS
  Collectors                   0.010     NS        0.014     NS
  Filterers                    0.051     NS        0.175     NS
  Total primary consumers      0.011     NS        0.016     NS
  Predators                    0.034     NS        0.006     NS
  Total invertebrates          0.013     NS        0.001     NS

                               Production

 Functional feeding group    [r.sup.2]     P

Leaf litter standing crop
  Scrapers                     0.058     NS
  Shredders                    0.794     (*)
  Collectors                   0.883     (***)
  Filterers                    0.307     NS
  Total primary consumers      0.868     (***)
  Predators                    0.971     (***)
  Total invertebrates          0.922     (***)

FBOM standing crop
  Scrapers                     0.216     NS
  Shredders                    0.001     NS
  Collectors                   0.014     NS
  Filterers                    0.134     NS
  Total primary consumers      0.007     NS
  Predators                    0.000     NS
  Total invertebrates          0.003     NS

Notes: The coefficient of determination ([r.sup.2]) and probability
values (P) of linear regressions were obtained by regressing annual
mean abundance (individuals/[m.sup.2]), biomass (g AFDM/[m.sup.2]),
or secondary production (g AFDM [multiplied by] [m.sup.-2]
[multiplied by] [yr.sup.-1]) (dependent variables) on leaf litter
or FBOM standing crop (g AFDM/[m.sup.2]) (independent variables).
These data include 5 yr of pretreatment and 4 yr of treatment (3
yr of litter exclusion plus 1 yr of small wood removal and litter
exclusion) (n = 9).

(*) P < 0.05; (***) P < 0.001; NS = not significant.


There were strong relationships between predators and prey over the 9-yr period. Predator abundance was strongly related to prey abundance ([r.sup.2] = 0.96, P [is less than] 0.001, Fig. 4D) in mixed substrate habitats. The lowest predator abundance measured during untreated years occurred during 1990 (asterisk, Fig. 4D), which was the year of greatest stream discharge. The poorest relationship between predators and primary consumers was for biomass ([r.sup.2] = 0.751, P [is less than] 0.005). Secondary production of predators was strongly related to both primary consumer production ([r.sup.2] = 0.916, P [is less than] 0.001) and total production ([r.sup.2] = 0.964, P [is less than] 0.001) in mixed substrates. The relationship between predators and total production is strong, in part because predators are included in both variables.

In bedrock habitats, only abundance of shredders and predators and biomass of shredders displayed a significant (P [is less than] 0.05) relationship with leaf litter standing crop over the 9-yr period of study (Table 13), which is in sharp contrast to the pattern just described for mixed substrates. There were no significant relationships between annual leaf litter standing crops and secondary production for any invertebrate group in bedrock habitats, which was different from the pattern for mixed substrates. In contrast with leaf litter, there were numerous significant relationships between invertebrates and FBOM standing crop on bedrock outcrops (Table 13). Production of collectors and total primary consumers, as well as total production, displayed significant positive relationships with mean annual FBOM standing crops on the bedrock outcrop substrates (Table 13). There was no significant association between annual moss standing crop and production of invertebrates (P [is greater than] 0.05) on bedrock outcrops. However, production of gatherers, shredders, and total primary consumers was significantly (P [is less than] 0.05 to [is less than] 0.02) related to total organic matter standing crop (FBOM and CBOM, including moss, leaf litter, and woody debris) on bedrock substrates.
TABLE 13. Long-term relationships between standing crop of leaf
litter (g AFDM/[m.sup.2]) and fine benthic organic matter (FBOM;
g AFDM/[m.sup.2]) in bedrock outcrop habitats and annual mean
abundance, mean biomass, and production of invertebrates in
C 55 for the years 1985, 1986, 1989, 1990, and September 1992 to
August 1997.

                               Abundance          Biomass

 Functional feeding group    [r.sup.2]    P    [r.sup.2]   P

Leaf litter standing crop
  Scrapers                     0.019     NS      0.359     NS
  Shredders                    0.530     (*)     0.526     (*)
  Collectors                   0.258     NS      0.065     NS
  Filterers                    0.215     NS      0.083     NS
  Total primary consumers      0.262     NS      0.352     NS
  Predators                    0.500     (*)     0.178     NS
  Total invertebrates          0.292     NS      0.302     NS

FBOM standing crop
  Scrapers                     0.006     NS      0.112     NS
  Shredders                    0.652     (*)     0.602     (*)
  Collectors                   0.510     (*)     0.221     NS
  Filterers                    0.022     NS      0.125     NS
  Total primary consumers      0.524     (*)     0.475     (*)
  Predators                    0.500     (*)     0.410     NS
  Total invertebrates          0.528     (*)     0.475     (*)

                                Production

 Functional feeding group      [r.sup.2]   P

Leaf litter standing crop
  Scrapers                       0.299     NS
  Shredders                      0.307     NS
  Collectors                     0.290     NS
  Filterers                      0.007     NS
  Total primary consumers        0.161     NS
  Predators                      0.010     NS
  Total invertebrates            0.115     NS

FBOM standing crop
  Scrapers                       0.187     NS
  Shredders                      0.441     NS
  Collectors                     0.627     (*)
  Filterers                      0.103     NS
  Total primary consumers        0.524     (*)
  Predators                      0.193     NS
  Total invertebrates            0.457     (*)

Notes: The coefficient of determination ([r.sup.2]) and probability
values (P) of linear regressions were obtained by regressing annual
mean abundance (individuals/[m.sup.2]), biomass (g AFDM/[m.sup.2]),
and secondary production (g AFDM [multiplied by] [m.sup.2]
[multiplied by] yr-1) (dependent variables) on leaf litter or FBOM
standing crop (independent variables). These data include 5 yr of
pretreatment and 4 yr of treatment (3 yr of litter exclusion plus
1 yr of small wood removal and litter exclusion) (n = 9).

(*) P < 0.05; NS = not significant.


Predator abundance on bedrock substrates was also strongly associated with that of prey ([r.sup.2] = 0.876, P [is less than] 0.001) over the 9-yr period, as was observed for mixed substrate habitats. There was no successive decline of predators and primary consumers with litter exclusion; predator and primary consumer abundance on bedrock substrates was lowest during the first year of exclusion (Fig. 5A). There was also a significant relationship between biomass of predators and that of primary consumers on bedrock substrates ([r.sup.2] = 0.798, P [is less than] 0.002) over the 9-yr period. Although the fourth year of treatment exhibited the lowest predator and primary consumer biomass, the pattern did not follow that exhibited by mixed substrate habitat, as biomass was lowest for each group during the first year of exclusion and fluctuated thereafter (Fig. 5B). Annual secondary production of predators also displayed a significant relationship with both primary consumer (r: = 0.68, P = 0.01) and total production ([r.sup.2] = 0.806, P [is less than] 0.002) over the 9-yr period on bedrock substrates (Fig. 5C). However, these latter two variables are not completely independent (see Discussion: Predator-prey relationships).

[Figure 5 ILLUSTRATION OMITTED]

DISCUSSION

The diversion of most of the energy fixed by auto-trophs to the detrital food web obfuscates classical plant-herbivore-predator food chains (Polis 1994, Polis and Strong 1996). Detritus is also not incorporated into the "green world hypothesis" of Hairston et al. (1960) and Fretwell (1977). Others have suggested that decomposers as a group must be food-limited (Hairston et al. 1960, Pomeroy 1991). Furthermore, organic energy flows up the food chain and at some point must determine biomass and production of higher trophic levels (Carpenter et al. 1991). As previously reported, ecosystem-level manipulations of detrital inputs are rare (Wallace et al. 1997); however, our manipulation clearly shows bottom-up effects that were propagated through primary consumers and top carnivores. In addition, our results are undoubtedly conservative, as we only succeeded in partially severing the linkage between these headwater streams and the surrounding forest (see Discussion: Predator-prey relationships).

Detrital resources and productivity of headwater streams

Throughout forested regions, headwater streams such as those we studied receive a significant amount of energy from a variety of allochthonous sources (Webster et al. 1995). Although examples of terrestrial-to-aquatic subsidies are best known (i.e., Strong 1992), examples of aquatic-to-terrestrial energy flow are also known (Polis and Hurd 1995, Polis and Strong 1996). Primary consumers in these detritus-based streams at Coweeta do not influence the rate of supply of their resources; however, they can influence standing crop of resources (Cuffney et al. 1990). Litter exclusion (Wallace et al. 1997) clearly showed that these forest streams are subsidized, donor-controlled systems. Nonetheless, we undoubtedly underestimated the extent of the stream's dependence on allochthonous inputs in our initial 3-yr exclusion and to a somewhat smaller extent by the present small woody debris removal. Our litter exclusion reduced inputs to ~5% of pretreatment values, which resulted in much lower standing crops of leaf litter in the treatment stream relative to that of the reference. A large mass of FBOM and CPOM (primarily woody debris) remained in the exclusion stream following the initial 3 yr of litter exclusion. Despite small wood removal at the start of the fourth year of exclusion, buried small woody debris amounting to several kg continued to resurface following storms and was removed by hand. Additional sources of terrestrially derived nutrients and organic matter also remained throughout our experiment and include the following. First, nutrients and dissolved organic carbon (DOC) continued to enter the stream by soil water as well as throughfall. Our manipulation did not curtail DOC inputs, although it reduced in-stream DOC generation (Meyer et al. 1998). Second, particulate organic matter from soils, and from throughfall, not only remained, but continued to enter. Bank runoff, measured for the past 2 yr, contributes an average 22.8 g AFDM of particulate organic matter/[m.sup.2] of wetted stream area each year (J. B. Wallace, E. R. Siler, and S. L. Eggert, unpublished data). Third, BOM existing in the stream prior to exclusion, as well as large woody debris ([is greater than] 10 cm diameter), remained in the stream bed. A significant decrease in small woody debris was found only following manual removal of small wood after 3 yr of exclusion (Table 3). Last, primary production is another obvious source of organic matter; however, in Coweeta headwater streams such production is very low and light-limited even during winter months by dense growths of riparian rhododendron (Webster et al. 1983, Lowe et al. 1986, Mulholland et al. 1997). Despite our efforts at eliminating or reducing stored organic particles within the treatment stream, [is greater than] 1 kg AFDM/[m.sup.2] remained during the fourth year of exclusion following small woody debris removal (Table 3). Thus, the actual importance of the terrestrial-aquatic linkages to aquatic productivity is undoubtedly greater than shown by our experiment. Complete severing of detrital inputs from the catchment will undoubtedly be very difficult, if not impossible.

It has been suggested that the ability of an ecosystem to resist displacement after disturbance is due in part to accumulated structure such as large organic matter storage in an ecosystem (Webster et al. 1975). A large standing crop of relatively resistant, organic matter that is slow to turn over can also enhance ecosystem stability by retaining and recycling nutrients and buffering against short-term environmental changes (O'Neill and Reichle 1980). Fisher and Likens (1973) also suggested that accumulated detritus in streams confers stability on them, such that streams are directly dependent on the surrounding forest for functional integrity as well as for reduced erodibility. Our results clearly support the concept that invertebrate community structure in these headwater streams is maintained to a large degree by accumulated organic matter. For example, after terrestrial litter inputs were curtailed, the reduction in abundance and biomass of most of the invertebrate community of mixed substrate habitats was a long, slow, continual process (Fig. 2). This is undoubtedly due in part to the relatively large store of organic matter in mixed substrates of the exclusion stream (Table 3), as well as to ongoing inputs not curtailed by litter exclusion. This reinforces the suggestion that several generations of invertebrate consumers may be required to detect food limitation in detrital food webs (Richardson and Neill 1991). However, despite the large residual sources of organic matter in mixed substrate habitats, most aquatic invertebrates displayed significant reductions in abundance or biomass, or both, in mixed substrates of the exclusion stream relative to the reference stream.

How important is terrestrially derived detritus to abundance, biomass, and secondary productivity of benthos in these Coweeta streams? In a nearby Coweeta stream that was subjected to four seasonal treatments with an insecticide, invertebrate abundance declined by 25% and biomass by ~79%, while secondary production was reduced 60% (Lugthart and Wallace 1992). By the fourth year of litter exclusion and small wood removal, invertebrates in the treatment stream were reduced 76% in abundance, 78% in biomass, and 78% in productivity from pretreatment values. Thus, the effects of reduction in allochthonous resources on invertebrate populations were at least as severe as seasonal treatments with an insecticide. In fact, other than the riffle habitat of a South Pacific Island stream, productivity after 4 yr of treatment in the mixed substrate habitats is lower than that of some 40 streams worldwide (Benke 1993). This underscores the importance of terrestrial detritus to invertebrate productivity of small, forested headwater streams such as those at Coweeta.

Stream geomorphology and effects of litter exclusion

If residual detritus buffers the system against change, why did bedrock-outcrop fauna exhibit no significant change during the 4-yr manipulation despite little stored organic matter in bedrock outcrop habitats (Fig. 3)? Steeper-gradient reaches of southern Appalachian streams are generally dominated by moss-covered bedrock substrate. Higher current velocities, less particle retention, and low standing crops of CPOM and FPOM (e.g., Table 3) generally characterize these bedrock outcrops (Gurtz and Wallace 1984, Huryn and Wallace 1987a). Benthic community structure on this bedrock is more characteristic of that downstream and is dominated by filterers, gatherers, and predators (Huryn and Wallace 1987a). Most of these animal groups rely primarily on transported organic matter and FPOM trapped within the moss and are less dependent on CPOM. During pretreatment and the first 2 yr of litter exclusion, FPOM export (seston) from the treatment stream exceeded that of the reference stream. However, by the third year of litter exclusion, total seston export from the treatment stream dropped to 81% of that from the reference stream and displayed a further decline to 73% of the reference levels during the first year of wood removal (J. B. Wallace, S. L. Eggert, J. R. Webster, and J. L. Meyer, unpublished data). Hence, there was sufficient material in transport to replenish FPOM associated with these bedrock habitats. Clearly, taxa associated with moss-covered bedrock habitats were less directly dependent on allochthonous resources, because no taxon on moss-covered bedrock showed a significant decrease in abundance or biomass during the 4-yr litter exclusion (Table 8). However, we anticipate that extension of litter exclusion for a longer period, e.g., a decade, would deplete both stored and transported FPOM. Eventually, long-term depletion of stored and transported FPOM would result in bedrock outcrop communities which could not sustain present levels of benthic abundance and biomass, as was observed for mixed substrates. Resources used by bedrock fauna are more displaced in time and by antecedent processes than those used by mixed substrate fauna; this is consistent with the functional similarity between bedrock reaches in headwaters and larger downstream segments.

Why do shredders display differences in response among mixed substrate and bedrock habitats in the litter exclusion stream (cf. Tables 6 and 7)? Total shredder biomass/[m.sup.2] of stream bottom was 6.1 (treatment) to [is greater than] 10 times (reference) greater for mixed substrates than moss-covered bedrock habitats. Plecopteran shredders, primarily Peltoperlidae and Leuctra spp., comprised 91 (treatment) to 92% (reference) of total shredder biomass on moss-covered bedrock substrates of these streams, vs. 20% of shredder biomass in the mixed substrate habitats. It has been suggested that early instars of plecopteran shredders such as Leuctra spp. are primarily collectors (Dobson and Hildrew 1992), which is consistent with the primary food resource available in the moss-covered bedrock habitat, FPOM. Unlike mixed substrate habitat, bedrock outcrop FPOM did not show a significant difference among the reference and treatment streams during the experiment (Table 3).

Based on mean monthly individual biomass, shredders on bedrock substrates of both streams were significantly smaller that those found in mixed substrates (P [is less than] 0.001, Mann-Whitney Rank Sum Test, n = 60, for each stream). Moss-covered bedrock substrates at Coweeta support primarily early instars of stonefly shredders. Average monthly mass per individual Leuctra on bedrock substrates in both streams was significantly smaller than that in mixed substrates (P [is less than] 0.004 for the reference stream and P [is less than] 0.02 for the treatment stream). Between-stream comparisons of monthly individual mass of peltoperlids in similar habitats were not significantly different for bedrock substrates (P [is greater than] 0.05); however, peltoperlids in mixed substrates were significantly larger in the reference stream (P [is less than] 0.001, Mann-Whitney Rank Sum Test). This suggests either increased mortality in later instars and/or decreased growth in mixed substrate habitats of the treatment stream.

Taxa showing no effects or delayed effects of resource exclusion

Scrapers were the only functional group that a showed a tendency to increase in production in mixed substrate habitats over the 4-yr treatment (Table 9). However, production of scrapers was low at the start (0.6% of total production) of the experiment and throughout the 4 yr of treatment (3.3% of total production). If primary production had not been limited by light, we would have anticipated a greater shift toward increased grazer production.

Filterers in mixed substrate habitats exhibited some decrease in abundance and biomass in the treatment stream, but these decreases were not significant (Table 6). Following 4 yr of treatment, productivity of filterers in the treatment and reference streams remained similar to that of the pretreatment year in mixed substrate habitats (Table 9). One filtering species, Diplectrona modesta, significantly increased in abundance in mixed substrate habitats of the treatment stream (Table 8). The failure of filterers to display a significant decrease during litter exclusion is undoubtedly related to increased concentrations of suspended organic matter, which increased during the initial years of treatment (J. B. Wallace and S. L. Eggert, unpublished data). The flushing of FBOM stored in the stream bed decreased during later years of exclusion. We anticipate that with continued depletion of FPOM, filterers will decline significantly.

Several taxa of detritus-feeding invertebrates that failed to show any significant decrease in abundance or biomass during the initial 3 yr of litter exclusion are those known to feed on woody debris or FBOM retained within the stream bed. Taxa known to feed on buried materials include sericostomatid caddisfly larvae, Fattigia pele (Wagner 1991), Diptera such as Molophilus, (Merritt and Cummins 1996), and Oligochaeta. Such residual organic matter was present throughout the 3-yr litter exclusion. Also, the standing crop of small woody debris in the treatment stream only became significantly different from the reference stream following its removal (Table 3). Other studies have noted that woody tissue is common in guts of a number of taxa for which we found no significant reductions during treatment. These include: Lipsothrix, which inhabit woody debris (Dudley and Anderson 1987), Paraleptophlebia, Lype, Tipula, and Sciaridae (Pereira et al. 1982).

There was also a change in the relative abundance of taxonomic groups of shredders during the 3-yr litter exclusion prior to removal of small woody debris. At the ordinal level, the major shredders in both streams were dipterans, trichopterans, and plecopterans. The proportion of shredder biomass in each of these groups changed more in the treatment than in the reference stream. Dipteran shredders (all Tipulidae) increased from 63 to 89% of total shredder biomass, trichopteran shredders decreased from 27 to 3%, and plecopteran shredders decreased somewhat less during the first 3 yr of litter exclusion. This shift toward a dominance of dipteran shredders (i.e., Lipsothrix and Tipula) during the first 3 yr of litter exclusion in the treatment stream is consistent with a shift toward wood-consuming taxa.

We collected subsamples of woody debris removed from the stream to measure invertebrates associated with wood substrates. Based on the total amount of wood removed and invertebrate abundance on these subsamples, we calculated abundance of animals on wood as a proportion of those collected in benthic core sampling during year 3 of litter exclusion. Invertebrates removed with wood averaged 11.5% of benthic abundance measured with the benthic corer during year 3. This estimate varied by functional group, as follows: scrapers = [is less than] 0.02%, shredders = 43%, gatherers = 8%, filterers = 8%, and predators = 29% of average benthic abundance. Acari, predaceous water mites, accounted for 65% of predators removed with wood and 19% of total invertebrates removed. The wood boring tipulid, Lipsothrix, represented 83% of the total shredders removed with woody debris. In fact, our estimates of Lipsothrix abundance in the small woody debris subsamples exceeded those measured with the benthic corer. In the benthic corer samples, Lipsothrix abundance was 51 individuals/[m.sup.2] (Appendix) vs. estimates of 209/ [m.sup.2] with removed wood. These results are not surprising, since the larger pieces of small woody debris, i.e., [is greater than] 6-10 cm diameter, are not sampled effectively with the benthic coring device. Estimates of standing crop of small woody debris made with the benthic corer were only 28% of the small woody debris removed (Wallace et al., in press).

Wood is well known as a poor food resource for freshwater organisms. Lignins, complex aromatic polymers formed from phenyl propanoid units, comprise 20-30% of woody tissue and serve as a barrier that protects cellulose and hemicellulose against degradative microbial enzymes (Shearer 1992). Dipteran shredders such as Tipula have been reported to assimilate up to 18-19% of the cellulose they ingest (Sinsabaugh et al. 1985), which is apparently mediated by bacteria in the rectal caecum rather than ingested microbial enzymes. Tipulids have an exceptionally alkaline gut (pH [is greater than] 11.0), which has high proteolytic activity and would destroy ingested microbial cellulases and hemicellulases (Martin et al. 1980, Sharma et al. 1984, Suberkropp 1992). Some guts of invertebrates such as Tipula in the exclusion stream contained [is greater than] 60% woody tissue (S. L. Eggert and J. B. Wallace, unpublished data). Highly alkaline guts have also been reported for a number of terrestrial insects that feed on woody and humic-rich materials. These include some Lepidoptera (Mishra 1991), wood-feeding beetles (Scarabaeidae and Passalidae, Terra and Ferreira 1994), and soil-feeding termites (Brune and Kuhl 1996). Highly alkaline conditions promote degradation and hydrolysis of lignocellulose, humic residues, and polyphenolic constituents of woody debris (Mishra 1991, Brune and Kuhl 1996). Hence, the greater persistence of dipteran shredders during the initial 3-yr litter exclusion may be due, in part, to their greater ability to utilize wood. Following removal of small woody debris in the fourth year of litter exclusion, all tipulids (Tipula, Lipsothrix, and Molophilus) decreased in mixed substrates of the treatment stream (Appendix). However, over the 4-yr treatment the decrease in either abundance or biomass for these shredders only approached significance (0.05 [is less than] P [is less than] 0.10, Table 8). Some small woody debris (121 g AFDM/[m.sup.2], Table 3) remained buried in the stream bed following removal, providing a limited energy source.

Leaf litter is more labile and has a higher breakdown rate than woody debris (e.g., Golladay and Webster 1988, Maharning and Barlocher 1996). Furthermore, aquatic hyphomycetes are more abundant on leaf litter than woody debris (Maharning and Barlocher 1996). However, available data do not suggest that, apart from the absence of leaf litter from the treatment stream, residual organic matter remaining in the channel of the treatment stream was poorer in nutritional quality than similar material in the reference stream (Meyer et al., in press). Although the standing crop of bacterial exopolymers was lower in the treatment stream, invertebrates in both streams derived a similar and significant portion of their carbon from bacteria or exopolymers (Hall and Meyer 1998). Additional evidence suggests that nutritional quality of residual organic matter was enhanced on epixylic biofilms in the treatment stream. Microbial activities (i.e., respiration, fungal biomass, extracellular enzyme activity) and decomposition of woody substrates were much higher in the exclusion stream than in the reference stream (Tank 1996, Tank and Webster 1998). The absence of leaf litter in C 55 apparently released epixylic microbes from competition for nutrients with microbes normally associated with decomposing leaves (Tank 1996, Tank and Webster 1998).

Long-term relationship between allochthonous detritus and production

During a 9.5-yr period of continuous organic matter export measurement made prior to exclusion of litter in C 55, there was a strong relationship between leaf litter export and maximum storm discharge (P [is less than] 0.001, Wallace et al. 1995b). Furthermore, most leaf litter removed from the wetted perimeter of the stream was retained in the narrow riparian zone, rather than exported to downstream reaches during storms (Wallace et al. 1995b). Prior to treatment, storms resulted in large annual fluctuations in organic matter standing crop in C 55. Wallace et al. (1995b) suggested that such fluctuations could potentially produce "bottlenecks" on benthic communities, especially leaf-shredding insects. The present study suggests that such effects extend well beyond leaf-shredding taxa and include many primary consumers and predators (Fig. 4A-F). Our long-term studies of C 55 suggest that even during untreated or "normal" periods, large differences in storm flows among years may influence secondary productivity of benthic communities within Coweeta streams (Fig. 4C). In addition to physical removal of invertebrates from substrate during high flow, abiotic forces such as storms may disrupt food resources, i.e., leaf litter, with consequences for invertebrate survival and growth. Hence, storms that remove organic matter may induce indirect long-term effects on abundance, biomass, and productivity of the benthic community (Fig. 4A-F). Human activities that alter stormflow frequency and intensity (e.g., impervious surfaces in the watershed, Dunne and Leopold 1978) would have a similar effect. The effect of drought and wet years on aquatic productivity is not limited to streams. For example, long-term productivity and trophic structure of a Gulf Coast estuary in Florida have been linked to freshwater inputs and alluvial river flow. River flow was strongly associated with annual rainfall in Georgia, well [is greater than] 100 km from the estuary (Livingston et al. 1997).

Predator-prey relationships

In both mixed substrate and bedrock substrates of the treatment stream, there was a significant relationship between abundance and biomass of predators and primary consumers, as well as with gatherers that constitute the majority of prey (R. O. Hall, J. B. Wallace, and S. L. Eggert, unpublished manuscript; Table 11). For each comparison of relationships between predators and their prey, the treatment stream displayed a higher [r.sup.2] than the reference stream (Table 11). In mixed substrate habitats, slopes for predator-prey relationships were also consistently higher in the treatment stream than the reference. The higher slope values indicate somewhat greater predator abundance and biomass per unit prey in the treatment stream compared with that of the reference stream. The difference in slopes between the exclusion and reference stream may reflect differences in intraguild predation in the two streams. R. O. Hall, J. B. Wallace, and S. L. Eggert (unpublished manuscript) found evidence that some of the largest biomass flows during winter in the litter excluded stream were predators consuming other predators, which was not observed in the reference stream. Slopes may also be steeper in the exclusion stream because its predators consume proportionally more prey per unit predator biomass than those of the reference stream. There is evidence that predators in the exclusion stream were consuming more of three common prey taxa than those in the reference stream (R. O. Hall, J. B. Wallace, and S. L. Eggert, unpublished manuscript).

If the linkage between predators and prey is strong, manipulation of the food base should produce a strong, measurable response in both primary and secondary consumers. This was observed following litter exclusion. Total abundance and biomass of predators decreased in mixed substrate habitats of the treatment stream following litter exclusion (Table 6), as did most major taxa of predators (Table 8). Total secondary production of predators declined by 76% of pretreatment values in the mixed substrates, which was very similar to the decrease in total invertebrate production (78% decrease).

Our data show a strong bottom-up effect of leaf litter on abundance and production of primary consumers that is propagated through secondary consumers. There was a positive relationship between primary consumer and predator production in both mixed substrate ([r.sup.2] = 0.916, P [is less than] 0.0001) and bedrock habitats ([r.sup.2] = 0.68, P = 0.0062) over a 9-yr period in the treatment stream. The strong positive relationship between predator and primary consumer production implies that predator production is closely linked with that of prey. There is an obvious statistical problem associated with the relationship between total production and predator production (i.e., nonindependence, because predators are in both variables). However, the inclusion of predators in both variables makes sense from a biological standpoint, as predators do eat other predators in these two streams (R. O. Hall, J. B. Wallace, and S. L. Eggert, unpublished manuscript). The slope of the relationship between total secondary production and predator production is ~0.35 (Fig. 4F) for the predominant mixed substrate habitats (=87% of stream area). The additional year of data for small woody debris removal did not change this slope from that reported previously by Wallace et al. (1997). This slope is in close agreement with known bioenergetic efficiencies reported for invertebrate predators (production/ingestion [approximately equals] 33-39%, Slanksy and Scriber 1982). The slope between total production and that of predators for bedrock outcrop habitats (0.23) is somewhat lower than that for mixed substrates; however, the slope values for the two habitats do not differ significantly (Zar 1984, test for difference among slopes).

The close agreement between general bioenergetic efficiencies reported for predators and the slope (0.35) for the relationship of predator production to total production over a 9-yr period has two major implications for mixed substrate habitats in this stream. First, predator production is apparently limited by that of prey, and, second, invertebrate predators growing at 35% efficiency would have to ingest most of the macroinvertebrate production to achieve measured rates of production. Thus, our results clearly show bottom-up effects demonstrated by litter exclusion; however, results also suggest the potential for top-down (predatory) effects (Wallace et al. 1997).

In natural environments, most prey are consumed by many species of predators. Most predator-prey-interaction studies suffer from a number of problems. These include concentrating on only one or two predators, limiting time scales to one generation or less, failing to consider multiple predators, and rarely accounting for intraguild predation (Sih et al. 1998). Most invertebrate predators consume multiple prey taxa (e.g., Allan 1983; R. O. Hall, J. B. Wallace, and S. L. Eggert, unpublished manuscript). In fact, many invertebrate predators feed at multiple trophic levels, including other predators (i.e., intraguild predation, sensu Polis and Holt 1992), which complicates conventional food chain theory (Polis 1994, Polis and Strong 1996; R. O. Hall, J. B. Wallace, and S. L. Eggert, unpublished manuscript). Intraguild predation on other invertebrate predators accounts for 16-27% of all predator ingestion in our study streams; hence, this predation is diffusely distributed among multiple taxa (R. O. Hall, J. B. Wallace, and S. L. Eggert, unpublished manuscript).

Diffuse predation may be an important reason why the effects of predators are often difficult to show at larger scales in many streams (however, see Power 1992, Huryn 1998). Hildrew (1992:317), reviewing stream food webs, described a difficulty in studies of predators: "The inference is that either predation is really dynamically trivial in running waters or the experiments are unable to detect the effects through some details of scale, timing, or design." In contrast to such diffuse predation is the specialized predation of a parasitic microsporidian on a dominant grazing caddisfly, which produced pronounced effects in Michigan streams (Kohler and Wiley 1997). However, diffuse consumption by predators, including intraguild predation and multiple prey, undoubtedly obscures the potential importance of predation. Detecting the potential importance of such diffuse predation in this detritus-based stream would probably be impossible without multi-year studies that assessed secondary production while simultaneously curtailing the detritus food base.

Although our litter exclusion clearly shows bottom-up effects, our results suggest a ratio-dependent positive correlation that is consistent with conditions where both bottom-up and top-down forces co-limit populations (Power 1992). Such models of predator and prey abundance and biomass over gradients of productivity are the subject of considerable debate (cf. Berryman 1992, Ginzburg and Akcakaya 1992, Slobodkin 1992, Abrams 1994, Gleeson 1994; see also Rosenzweig 1973, Oksanen et al. 1981, Diehl et al. 1993). Power (1992) succinctly summarized these views with respect to top-down and bottom-up forces in food webs. However, such models are generally for single-predator and single-prey systems and are not amenable to multiple predators and prey at the ecosystem level. Spatial scales also influence such studies as models of algae-snail responses to nutrient additions in streams, which have noted local prey-dependent functional responses that gave results similar to ratio-dependent responses when integrated over large areas and times (Blaine and DeAngelis 1997). Although they were not analyzing production data, Warren and Gaston (1992) suggested that such ratio dependency between predators and prey might be linked to energy flow. From a larger ecosystem perspective, production of prey, as well as production of predators falling victim to intraguild predation (sensu Polis and Holt 1992) limits energy available to secondary consumers. Thus, ecosystem-level production and bioenergetics may constrain energy available to secondary consumers. As noted above, bioenergetic efficiencies reported for invertebrate predators appear to be the best explanation for the 9-yr relationship between secondary production and predator production. In a larger, more productive stream than the headwater streams at Coweeta, it was shown that most ([is greater than] 80%) of the benthic invertebrate productivity is required to support observed fish production (Huryn 1996). Thus, consumption of most benthic production by predators is not unrealistic.

Previously, we suggested that litter exclusion avoided the vast array of indirect effects often associated with curtailing litter inputs to streams, i.e., logging and land-use changes, and showed that allochthonous detritus alone plays a major role in productivity of headwater stream communities (Wallace et al. 1997). However, this previous analysis underestimated the importance of terrestrial-stream linkages. Consumption of woody debris increased in the treatment stream during litter exclusion (R. O. Hall, J. B. Wallace, and S. L. Eggert, unpublished manuscript). Removal of small woody debris during the fourth year of the study resulted in an additional 47% decrease in abundance and 50% decline in biomass of benthic invertebrates compared to the third year of litter exclusion. Significant (P [is less than] 0.05, RIA) declines in biomass of shredders, collectors, and total primary consumers occurred in mixed substrate habitats between year 3 (litter exclusion alone) and year 4 (litter exclusion coupled with small woody debris removal). During this same period, total secondary production decreased by 48%. In general, the changes in benthic abundance, biomass, and production in mixed substrate habitats following removal of small woody debris exceeded those observed between successive years of litter exclusion. Most studies have focused on the role of large woody debris in stream ecosystems. The present study shows that small woody debris alone plays an important role as a food resource.

In summary, our results clearly demonstrate the importance of food web subsidies from one ecosystem to another. This study strongly supports bottom-up regulation of the benthos in detrital-based streams and links predator production to that of prey. Furthermore, this study has underestimated the impact of bottom-up regulation of forested headwater streams, as we have ongoing sources of inputs, i.e., nutrients, DOC, throughfall, and soil organic matter, as well as large woody debris and retained organic matter. It may be impossible effectively to curtail all detrital inputs into an ecosystem that is situated lower in the landscape than the donor ecosystem. Despite C 55's large in situ storage of organic matter, as well as the ongoing "leakage" from the surrounding forest, our study demonstrates the importance of terrestrial-aquatic linkages to maintaining productivity of headwater streams.

ACKNOWLEDGMENTS

This research was supported by grants DEB-9207498 and DEB-9629268 from the National Science Foundation. A portion of J. B. Wallace's time was funded by CSRS project GEO 00784. Dr. Wayne T. Swank and various personnel at the Coweeta Hydrologic Laboratory provided on-site assistance. John Hutchens provided valuable comments on an earlier draft of the manuscript. We thank Dr. Cliff Dahm and two anonymous referees for constructive comments on the manuscript. We thank the following individuals for technical and laboratory assistance: James Beck, Barbara Bennett, Dr. K. Chung, Eric Fish, Stephanie Greene, David Giles, John Hutchens, Erich Linnemann, Dave Hart, Dr. Robert Hall, Patricia Huback, Brian Keeley, Courtney King, Matt McTammany, Matt Neatrour, Chris Peredney, Scott Stroud, and Steve Zucker.

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APPENDIX

Abundance, A (individuals/[m.sup.2]), mean annual standing stock
biomass, B (mg AFDM/[m.sup.2]), and secondary production, P (mg
AFDM [multiplied by] [m.sup.2] [multiplied by] [yr.sup.-1]), for
major taxa in each functional feeding group found in the mixed
substrate and moss-covered bedrock substrate of Catchment 53
(C 53 = reference stream) and Catchment 55 (C 55 = treatment
stream). Order = noninsects (NI), or insect orders, where C =
Coleoptera, D = Diptera, E = Ephemeroptera, O = Odonata, P
= Plecoptera, and T = Trichoptera. CPI = cohort production interval
in days or, where noted, the assumed annual P/B that was used for
production calculations. Years are as follows: PreTmt =
pretreatment year (September 1992 to August 1993); LE-1, LE-2,
LE-3 = litter exclusion years 1 through 3 for C 55 (September 1993
to August 1996); WR-1 = small wood removal combined with ongoing
litter exclusion for C 55 (September 1996 to August 1997).

          Taxon              Order         CPI        Site   Year

Scrapers
  Epeorus sp.                  E      340             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Baetis sp.                   E      120             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Neophylax sp.                T      213             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Other scrapers([double                              C 53   PreTmt
    dagger])                                                 LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Total scrapers                                      C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

Shredders
  Leuctra spp.                 P      340             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Peltoperlidae                P      540             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Lepidostoma spp.             T      246             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Pycnopsyche sp.              T      275             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Fattigia pele                T      664             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Molophilus sp.               D      365             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Tipula sp.                   D      310             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Lipsothrix sp.               D        5([dagger])   C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Other                                               C 53   PreTmt
    shredders([sections])                                    LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Total shredders                                     C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

Gatherers
  Paraleptophlebia sp.         E      340             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Serratella sp.               E      330             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Stenonema sp.                E      340             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Amphinemura sp.              P      300             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Lype diversa                 T      332             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Chironomidae                 D      ([parallel])    c 53   PreTmt
    (= non-Tanypodinae)                                      LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Sciaridae                    D      365             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Copepoda                    NI       18([dagger])   C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Nematoda                    NI        5([dagger])   C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Oligochaeta                 NI        5([dagger])   C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Other                                               C 53   PreTmt
    gatherers([paragraph])                                   LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Total gatherers                                     C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

Filterers
  Diplectrona modesta          T      332             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Parapsyche cardis            T      332             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Other filterers(#)                                  C53    PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Total filterers                                     C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

Predators
  Cordulegaster sp.            O     1140             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Lanthus sp.                  O      660             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Sweltsa sp.                  P      630             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Beloneuria sp.               P      660             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Isoperla spp.                P      300             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Rhyacophila spp.             T      340             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Pseudogoera singularis       T      365             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Ceratopogonidae              D      365             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Hexatoma spp.                D      365             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  nr. Pedicia sp.              D      340             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Dicranota spp.               D      310             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Glutops sp.                  D      365             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Tanypodinae                  D      340             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Empididae                    D      340             C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Acari                       NI        5([dagger])   C 53   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Other invertebrate                                  C 53   PreTmt
    predators([dagger]                                       LE-1
    [dagger])                                                LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Total invertebrate                                  C 53   PreTmt
    predators                                                LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

  Salamanders                                         C 53   PreTmt
    ([double dagger]                                         LE-1
    [double dagger])                                         LE-2
                                                             LE-3
                                                             WR-1
                                                      C 55   PreTmt
                                                             LE-1
                                                             LE-2
                                                             LE-3
                                                             WR-1

                               Mixed substrates

          Taxon                A       B      P

Scrapers
  Epeorus sp.                     0      0      0
                                  0      0      0
                                  1      2      7
                                  1      0      0
                                  2      3     16
                                  8      0      2
                                  2      0      0
                                  8      0      3
                                  0      0      0
                                  2      2     11

  Baetis sp.                      5      0      3
                                  0      0      0
                                  0      0      0
                                  2      0      0
                                  2      0      1
                                  1      0      0
                                  4      0      1
                                  8      0      1
                                  2      0      1
                                  0      0      0

  Neophylax sp.                  22      1      8
                                  6      0      2
                                  0      0      0
                                  0      0      0
                                 28      0      3
                                  2      0      2
                                  4      0      1
                                 70      1     10
                                 30      2     20
                                 30      0      4

  Other scrapers([double         17      0      2
    dagger])                     36      3     14
                                  3      2      3
                                  3      1      2
                                 11      1      3
                                551      5     29
                                367      5     33
                                215      3     12
                                392      8     31
                                414      5     23

  Total scrapers                 44      2     13
                                 42      3     16
                                  4      4     10
                                  5      1      2
                                 43      5     24
                                562      6     33
                                377      5     35
                                302      4     26
                                423     10     51
                                447      8     37

Shredders
  Leuctra spp.                  495     20    110
                                599     40    204
                               1009     60    292
                                993     29    196
                               1634     34    252
                                464     16    103
                                157      5     33
                                240      9     24
                                229      7     43
                                223      3     29

  Peltoperlidae                 416     71    273
                                425    117    520
                                309    102    354
                                723     87    425
                                132     42    149
                                220     24    112
                                277     28    169
                                116     19     94
                                131      5     54
                                 86      6     40

  Lepidostoma spp.               18      5    350
                                499     43    383
                                864     54    445
                               1320     66    708
                                273     14    139
                                  4      1    115
                                106     11    103
                                  3      0      0
                                 11      0      4
                                  9      0      4

  Pycnopsyche sp.                63    242    980
                                286     95    853
                                158    152    882
                                182    131    852
                                 88    122    757
                                 66     77    255
                                 43      3     50
                                 13      1      2
                                  0      0      0
                                  1      0      1

  Fattigia pele                  72     59    129
                                 43     55    129
                                 42     37     69
                                 91    108    221
                                126    108    239
                                 23     24     59
                                 18     21     55
                                  9      4      9
                                 28      5     17
                                  9      6     15

  Molophilus sp.                220     47    272
                                140     39    208
                                458     53    292
                                364     75    383
                                228     48    234
                                128     19    121
                                 48     14     82
                                 22      3     10
                                 66     11     60
                                 28      3     21

  Tipula sp.                     34    246   1706
                                 39    178   1188
                                 63    197   1054
                                 81    385   2252
                                 34    230    964
                                 40    226    996
                                 21    193   1189
                                  8    153    397
                                 10    154    653
                                  3     29    129

  Lipsothrix sp.                 10      0      0
                                  6     15     77
                                  3      6     31
                                 15     44    222
                                  3      5     24
                                  1      7     35
                                  2      2     11
                                  2      1      5
                                 51     30    148
                                  0      0      0

  Other                          31     11     31
    shredders([sections])        13     18     64
                                 54     52    229
                                 74     56    185
                                 23      7     18
                                  8      8     15
                                 19      9     26
                                 13      3      4
                                 20      9     25
                                  5      2      4

  Total shredders              1360    700   3851
                               2052    600   3625
                               2960    713   3646
                               3843    980   5443
                               2541    611   2774
                                954    401   1810
                                692    287   1718
                                425    193    545
                                545    222   1003
                                363     48    242

Gatherers
  Paraleptophlebia sp.           66      9     37
                                100     11     51
                                179      8     62
                                 53      8     27
                                 51     10     63
                                134      5     32
                                 54      3     18
                                158      3     17
                                 36      2     12
                                 52      1     14

  Serratella sp.                  9      7     41
                                 20     12     51
                                  0      0      0
                                  2      0      1
                                  4      0      2
                                 14      6     36
                                  8      0      2
                                 73      5     45
                                 37      6     43
                                 79      6     43

  Stenonema sp.                  12     23     79
                                 47     27    117
                                103     34    216
                                 72     29    155
                                 71     26    120
                                 14     22     87
                                 13      3     18
                                 10      2     14
                                  6      1      4
                                  0      0      0

  Amphinemura sp.                12      4     18
                                 34      2     14
                                 58      4     25
                                165      7     42
                                143      5     35
                                 23      2     13
                                 23      1      8
                                 34      1      9
                                 62      2     13
                                 56      1     15

  Lype diversa                   72      8     38
                                 76      7     39
                                 96      5     27
                                 76      7     44
                                137     16    109
                                 41      5     26
                                 47      4     21
                                 77      4     24
                                244     14    109
                                 12      1      9

  Chironomidae               23 789     84   1169
    (= non-Tanypodinae)      25 923     59   1234
                             39 105     98   1694
                             30 747     99   1570
                             35 666    139   2901
                             16 448     57    780
                               9466     26    410
                             13 288     21    515
                               7024     15    304
                               3874      9    184

  Sciaridae                      64      5     16
                                 70      3     11
                                331     21     83
                                635     19     83
                                228      5     33
                                 95      4     14
                                 83      4     18
                                102      6     22
                                 21      2      6
                                 15      1      3

  Copepoda                   14 418     14    260
                             26 430     26    475
                             39 525     40    711
                             29 431     29    529
                             33 507     34    603
                               5942      6    107
                               5000      5     90
                               1454      2     25
                               1272      1     23
                                320      0      5

  Nematoda                   11 371      9     43
                             13 111     10     50
                             11 204      9     43
                             14 792     14     69
                             17 899     15     75
                               6927      5     26
                               5876      5     23
                               2516      2     10
                               3897      4     19
                               1498      2      8

  Oligochaeta                  3906    177    883
                               4268     81    404
                               3780     50    251
                               3801     78    389
                             10 817     69    347
                               1281     45    223
                               1308     30    149
                                851     31    154
                                937     17     86
                                596      9     46

  Other                          17      0      2
    gatherers([paragraph])      114     14     77
                                  1      1      3
                                  9      0      1
                                  4      2     14
                                 21      2     11
                                 13      1      4
                                 33      0      1
                                 33      0      1
                                 20      0      1

  Total gatherers            53 734    339   2586
                             70 194    252   2524
                             94 383    269   3114
                             79 783    289   2908
                             98 527    320   4302
                             30 940    158   1356
                             21 893     81    760
                             18 595     77    835
                             13 569     65    619
                               6521     31    327

Filterers
  Diplectrona modesta           167     57    315
                                166     14     88
                                 64     19    109
                                 42     10     43
                                 85     24     98
                                271     33    236
                                 95     20    116
                                157     19     90
                                192     29    152
                                119     14     92

  Parapsyche cardis               2     20     51
                                  0      0      0
                                  1      0      2
                                  1      3     16
                                 10      1     14
                                  1      0      2
                                  6      0      2
                                  3      4     10
                                  1      0      0
                                  4      1     11

  Other filterers(#)            120     25    107
                                204     14     83
                                302     31    157
                                461     23    149
                                272     11     60
                                 51      2     18
                                 38      1     15
                                 43      4     18
                                 30      4     21
                                 16      4     10

  Total filterers               288    102    473
                                370     29    171
                                367     50    268
                                504     36    209
                                367     36    173
                                323     35    256
                                139     21    133
                                203     26    118
                                222     33    173
                                139     19    112

Predators
  Cordulegaster sp.              37     96    207
                                 95    236    359
                                 16     85     87
                                 27    184    356
                                 18    145    235
                                 40     72    133
                                 23     52     70
                                  4     27     24
                                  3     24     30
                                 12     42     95

  Lanthus sp.                    26    148    281
                                 55    177    455
                                 67    252    612
                                 98    178    439
                                 35    132    307
                                 30     86    258
                                 24     70    224
                                  8      6     23
                                 10     19     42
                                 15     18     50

  Sweltsa sp.                    57      2     10
                                 16      0      2
                                 13      1      1
                                  9      2      5
                                 16      1      3
                                 73      8     26
                                 66      5     14
                                 95      7     19
                                 46      3      9
                                 37      2      6

  Beloneuria sp.                 50     94    216
                                 91     89    318
                                124    229    600
                                145    150    411
                                 31    108    286
                                 11     22     67
                                 10     18     58
                                  9      8     16
                                 16      3     16
                                  5      1      8

  Isoperla spp.                  39     10     47
                                189     13    140
                                 82     20    108
                                134      6     48
                                136      8     73
                                 40      6     32
                                 53      8     77
                                 38      3     19
                                 34      1     11
                                 32      1     10

  Rhyacophila spp.               97     10     55
                                 58     31    164
                                 36     16     67
                                 88     19    105
                                 62     16     82
                                 31      8     37
                                 84      4     39
                                 85      5     43
                                 34      6     28
                                 10      2     12

  Pseudogoera singularis         21      3     12
                                 13      3     10
                                 42     15     29
                                 56      1      6
                                 12      3      6
                                  4      0      1
                                  2      0      2
                                  1      0      0
                                  5      0      0
                                  0      0      0

  Ceratopogonidae              2106    100    447
                               3606    113    673
                               3679    162    757
                               4861    181   1681
                               2196    104    511
                               1633     62    314
                               1226     48    259
                                941     38    195
                                916     27     61
                                378     14     69

  Hexatoma spp.                 352     84    566
                                558     61    571
                                621    122    604
                               1091    131    789
                                585    100    546
                                510     75    508
                                210     33    247
                                121     41    233
                                 29      3     18
                                 95     13     65

  nr. Pedicia sp.                40     24    132
                                 65     27    186
                                 32     79    439
                                117     49    259
                                 69     54    296
                                 18     19    106
                                 22     12     67
                                  1      1      2
                                  6      3     11
                                  2      0      2

  Dicranota spp.                 70      6     28
                                114      5     23
                                101     12     96
                                 82     16    116
                                 45     16     82
                                 16      1      5
                                 19      0      3
                                 29      1      9
                                 32      1     10
                                 33      3     18

  Glutops sp.                     9     63    199
                                  6     15     51
                                  4     22     62
                                 13     10     76
                                  2     12     24
                                  4     29     61
                                  5     27     91
                                  2      8     16
                                  2      4     19
                                  1      3      8

  Tanypodinae                  1195      5     43
                               1884      9     71
                               2129     10     73
                                955      6     42
                               1705     13     91
                                710      2     19
                                807      1     14
                                417      1      6
                                 94      0      2
                                247      0      6

  Empididae                     260      9     59
                                583      3     28
                                112      2     16
                                 69      1      4
                                 45      1      5
                                222      3     26
                                320      2     16
                                 16      0      1
                                 19      0      1
                                 10      0      1

  Acari                        2415      6     32
                               2707      7     36
                               1463      4     20
                               1934      5     26
                               3250      9     43
                               1539      4     21
                               1583      4     21
                                493      1      7
                                643      2      9
                                387      1      5

  Other invertebrate             54     12     23
    predators([dagger]           52     12     20
    [dagger])                   130     17     92
                                136     45    344
                                399     13     51
                                 11      7     16
                                 14      7     35
                                 18      5     19
                                 15      3     12
                                 72      7     33

  Total invertebrate           6827    672   2357
    predators                10 092    801   3106
                               8650   1046   3661
                               9815    983   4706
                               8606    734   2639
                               4892    403   1629
                               4469    291   1237
                               2277    151    630
                               1905     97    279
                               1333    107    386

  Salamanders                     5     58     93
    ([double dagger]              9     59    113
    [double dagger])             16    181    336
                                  7     69    153
                                  4     53    134
                                  4     29     62
                                  1      4     13
                                  0      0      0
                                  1     11     26
                                  1     26     32

                              Bedrock substrates

          Taxon                A       B     P

Scrapers
  Epeorus sp.                    23    48    137
                                 15     1     17
                                 13    13     56
                                  7     3     26
                                 28    26    102
                                 11    15     69
                                  4     0      1
                                 11     2      3
                                 15    26     99
                                 20    19    104

  Baetis sp.                     64     2     25
                                 25     0      5
                                200     3     58
                                165     2     43
                                236     2     63
                                 60     2     28
                                  4     0      2
                                 35     0      4
                                 27     1     12
                                 44     2     28

  Neophylax sp.                  27     4     23
                                 65     1     13
                                 36     0      4
                                 14     1      7
                                 14     1      3
                                 43     1      7
                                 36     1      8
                                 68     2     15
                                214     2     39
                                146     1     15

  Other scrapers([double         60     6     18
    dagger])                     52     7     20
                                 34     7     24
                                 93    15     34
                                 70    11     25
                                148    18     33
                                107     7     21
                                191     9     23
                                437    26     63
                                155    12     29

  Total scrapers                174    59    202
                                157     9     54
                                283    24    142
                                279    20    110
                                347    39    193
                                263    36    137
                                151     8     32
                                304    13     45
                                693    55    213
                                366    33    176

Shredders
  Leuctra spp.                   74     4     20
                                 88     3     15
                                 58     2     12
                                114     3     16
                                 35     1      5
                                 72     4     20
                                 14     0      2
                                 40     1      5
                                 60     1      7
                                 42     0      3

  Peltoperlidae                 476    78    353
                                532    70    384
                                589    41    290
                               1066    82    543
                                386    33    204
                                541    39    306
                                583    37    285
                                341    26    185
                                716    37    339
                                202    18    121

  Lepidostoma spp.               26     0      7
                                 14     0      1
                                 33     1      7
                                 76     2     29
                                 21     1      7
                                  4     0      1
                                 14     0      2
                                  6     0      0
                                 30     0      5
                                  9     0      1

  Pycnopsyche sp.                 1     0      0
                                 68     7    112
                                  5     0      7
                                 18     2     40
                                  0     0      0
                                  1     0      3
                                  0     0      0
                                  0     0      0
                                  1     0      1
                                  0     0      0

  Fattigia pele                   0     0      0
                                  0     0      0
                                  0     0      0
                                  4     0      1
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  1     0      1

  Molophilus sp.                  0     0      0
                                  0     0      0
                                  0     0      0
                                  1     0      1
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0

  Tipula sp.                      1     0      7
                                  0     0      0
                                  1     0     90
                                  0     0      0
                                  0     0      0
                                  4     8     83
                                  2     9     88
                                  0     0      0
                                  2     5     55
                                  1     1     16

  Lipsothrix sp.                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  4     3     13
                                  0     0      0

  Other                           0     0      0
    shredders([sections])         0     0      0
                                  9     2      6
                                 25     3      7
                                  1     1      2
                                  1     0      0
                                 12     2      5
                                  0     0      0
                                  1     0      0
                                  1     1      2

  Total shredders               578    82    387
                                702    80    512
                                695    46    411
                               1305    92    637
                                443    35    218
                                622    52    412
                                625    49    382
                                387    27    190
                                814    44    420
                                255    21    144

Gatherers
  Paraleptophlebia sp.            6     1      4
                                  5     0      1
                                  8     0      0
                                  6     0      1
                                  1     0      0
                                 69     0      7
                                  6     0      1
                                  9     1      3
                                  6     0      1
                                  5     0      2

  Serratella sp.                374   129    711
                                484    37    284
                                340    48    306
                                220    47    250
                                128    47    179
                                133    34    230
                                 46     7     47
                                140    26    151
                                 90    18    111
                                 34     6     36

  Stenonema sp.                   1     0      0
                                  4     1      6
                                  6     0      2
                                  1     0      2
                                  4     1      5
                                 19     1      9
                                  2     0      1
                                  4     5     13
                                  1     0      1
                                  1     0      0

  Amphinemura sp.               585    22    183
                                616    20    189
                                849    36    274
                                808    18    146
                               1138    17    239
                                458    32    236
                                203    10     90
                                938    21    210
                                941    34    219
                                778    30    273

  Lype diversa                    0     0      0
                                  3     0      0
                                  0     0      0
                                  1     0      0
                                  0     0      0
                                  1     0      0
                                  0     0      0
                                  0     0      0
                                  4     0      1
                                  0     0      0

  Chironomidae               12 755    32    592
    (= non-Tanypodinae)        7967    11    283
                             11 942    31    648
                               7547    23    422
                               7675    21    420
                             10 282    20    418
                               4363    10    221
                               8873    18    460
                             14 066    26    569
                             10 302    19    486

  Sciaridae                       2     0      1
                                  5     0      0
                                  3     0      0
                                 12     0      2
                                  0     0      0
                                  1     0      0
                                  0     0      0
                                  1     0      0
                                  0     0      0
                                  0     0      0

  Copepoda                     1086     1     20
                               1588     2     29
                               1400     1     25
                                719     1     13
                                207     0      4
                                490     1      9
                                528     1      9
                                618     1     11
                                466     1      9
                                155     0      4

  Nematoda                      294     0      1
                                250     0      1
                                250     0      1
                                252     0      1
                                196     0      1
                                252     0      1
                                 97     0      0
                                264     0      1
                                172     0      1
                                131     0      1

  Oligochaeta                   431     1      6
                                176     1      7
                                188     0      2
                                128     0      2
                                 49     0      1
                                465     1      7
                                581     2      7
                                880     3     16
                               1450     4     19
                                234     1      3

  Other                          21     0      1
    gatherers([paragraph])        0     0      0
                                  0     0      0
                                  9     0      0
                                  0     0      0
                                 21     0      1
                                 30     0      1
                                 10     0      0
                                 50     0      2
                                 44     0      2

  Total gatherers            15 555   187   1520
                             11 096    72    799
                             14 986   118   1258
                               9704    90    839
                               9397    87    849
                             12 191    90    918
                               5856    30    378
                             11 736    74    865
                             17 246    82    934
                             11 684    56    805

Filterers
  Diplectrona modesta           273    18    190
                                321    17    151
                                406    17    186
                                 71    13     90
                                161     6     56
                                157    24    182
                                 80    14     71
                                663    14    142
                                 57    11     74
                                 89     9     40

  Parapsyche cardis             741   403   3464
                                372   144    925
                                406   211   1184
                                823   295   1900
                                475   295   2281
                                595   310   2985
                                237    48    312
                                288   166    802
                                593   146   1112
                                690   140   1491

  Other filterers(#)            114     8     49
                                 63     4     24
                                399     5     44
                                683    18    221
                                321     8     62
                                155     3     36
                                 40     3     21
                                 54     1     13
                                134     6     80
                                119     5     21

  Total filterers              1127   429   3704
                                756   164   1099
                               1211   233   1414
                               1576   326   2211
                                957   309   2399
                                906   337   3202
                                356    65    404
                               1006   180    957
                                784   162   1265
                                898   154   1552

Predators
  Cordulegaster sp.               0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0

  Lanthus sp.                     0     0      0
                                  0     0      0
                                  1     3     14
                                  3     0      0
                                  1     0      3
                                  1    16     38
                                  0     0      0
                                  1    16     14
                                  5    12     39
                                  0     0      0

  Sweltsa sp.                     3     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  2     1      2
                                  0     0      0
                                  0     0      0
                                  4     0      0
                                  0     0      0
                                  0     0      0

  Beloneuria sp.                 18    15     60
                                 33    13     64
                                 12    10     44
                                 43    13     58
                                 16     9     57
                                  6    19     32
                                 15     3     15
                                 19     8     24
                                 48    10     54
                                 16     3     12

  Isoperla spp.                 130    45    252
                                102     6     66
                                 98    18    102
                                 66     8     49
                                 75    16     83
                                 55    12     78
                                 48     3     32
                                 53     6     47
                                 16     0      4
                                 69     3     34

  Rhyacophila spp.              141    23    202
                                 84    21    139
                                 98    11     84
                                 57    22    138
                                 43     7     41
                                155    29    160
                                 31     7     43
                                 57     9     55
                                 45    11     68
                                 34     8     12

  Pseudogoera singularis        109     7     58
                                169     3     25
                                 69     2     14
                                196     5     29
                                 52     1     17
                                 76     0      7
                                 44     1      6
                                 60     2      8
                                190     2     25
                                 76     3     39

  Ceratopogonidae               244     9     49
                                163     5     26
                                 68     3     16
                                 78     5     40
                                 48     1      9
                                 77     4     18
                                 88     2     13
                                 37     2     11
                                358     4     61
                                 20     2      8

  Hexatoma spp.                   9     1      5
                                  2     1      3
                                  2     0      1
                                  4     0      2
                                  6     1      6
                                  5     1     11
                                  0     0      0
                                  1     0      1
                                 57     1      8
                                 12     2     10

  nr. Pedicia sp.                 0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  8     1      8
                                  0     0      0

  Dicranota spp.                137     3     28
                                 70     2     15
                                126     2     35
                                111     3     27
                                 67     1     11
                                 94     3     26
                                 37     0      3
                                 52     1      5
                                 77     6     52
                                 27     2     12

  Glutops sp.                     0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  0     0      0

  Tanypodinae                   231     1      6
                                189     0      3
                                407     1     12
                                 61     0      2
                                926     1     21
                                175     1      7
                                133     0      2
                                155     1      4
                                 58     0      1
                                255     0      6

  Empididae                     241     4     32
                                102     2     12
                                147     2     15
                                 27     0      2
                                 98     3     12
                                260     6     35
                                 77     1      4
                                103     2     11
                                 66     2      8
                                 28     0      3

  Acari                        1737     5     24
                               1974     5     26
                               1877     5     25
                               1486     4     20
                               1336     4     18
                               1600     4     22
                               1054     3     14
                               1487     4     20
                               1557     4     21
                                984     3     13

  Other invertebrate             43     1      6
    predators([dagger]           44     1      4
    [dagger])                    11     0      1
                                 19     0      1
                                 55     2      5
                                 27     2     12
                                 23     1      4
                                 45     0      2
                                 58     4     13
                                 53     1      2

  Total invertebrate           3043   113    722
    predators                  2932    58    382
                               2915    57    363
                               2152    61    367
                               2726    48    284
                               2532    97    446
                               1549    20    136
                               2074    50    202
                               2542    56    362
                               1572    25    149

  Salamanders                     0     0      0
    ([double dagger]              0     0      0
    [double dagger])              1    29     29
                                  2    22     43
                                  1    38     67
                                  0     0      0
                                  0     0      0
                                  0     0      0
                                  3    36     60
                                  1    18     34

([dagger]) Assumed annual P/B.

([double dagger]) Other scrapers = Ectopria sp. (C), Elmidae (C),
and Hydroptila sp. (T).

([sections]) Other shredders = Psilotieta sp. (T), Limonia sp. (D),
and Anchytarsus sp. (C).

([parallel]) Chironomidae production measured using community
growth are from Huryn (1990).

([paragraph]) Other gatherers = Soyedina sp. (P), Nymphomyiidae
(D), Ormosia sp. (D), and Syrphidae (D).

(#) Other filterers = Diplectrona metaqui (T), Wormaldia spp. (T),
Dolophilodes distinctus (T), Dixa sp. (D), Simulium sp. (D), and
Sphaeridae (NI).

([dagger][dagger]) Other invertebrate predators = Malirekus hastatus
(P), Molanna blenda (T), Pedicia sp. (D), Pilaria sp. (D),
Pseudolimnophila sp. (D), Rhabdomastix sp. (D), and Dolichopodidae
(D), and Turbellaria (NI).

([double dagger][double dagger]) Salamanders = Desmognathus spp.
(average CPI = 880) and Eurycea sp. (average CPI = 365).


J. BRUCE WALLACE,(1,2,4) S. L. EGGERT,(1) JUDY L. MEYER,(2) AND J. R. WEBSTER(3)

(1) Department of Entomology, University of Georgia, Athens, Georgia 30602 USA

(2) Institute of Ecology, University of Georgia, Athens, Georgia 30602 USA

(3) Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 USA

Manuscript received 13 March 1998; revised 16 November 1998; accepted 5 January 1999.

(4) E-mail: wallace@sparc.ecology.uga.edu
COPYRIGHT 1999 Ecological Society of America
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Author:Wallace, J. Bruce; Eggert, S.L.; Meyer, Judy L.; Webster, J.R.
Publication:Ecological Monographs
Article Type:Poem
Geographic Code:1USA
Date:Nov 1, 1999
Words:23677
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