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Ants create hummocks and alter structure and vegetation of a Montana fen.

INTRODUCTION

Ants are abundant in most ecosystems and can have major effects on the functioning of these systems (Petal, 1978). They are important herbivores and predators (Davidson et al., 1980); they move large quantifies of soil (Lyford, 1963); and they protect plants (Huxley, 1980) and disperse their seeds (Handel et al., 1981).

Although ants have been extensively studied in most habitats from deserts to tropical forests (Holldobler and Wilson, 1990), there are few studies on the ecology of ants in peatlands even though these ecosystems occupy approximately 10% of the landscape N of 50 [degrees] Lat (Gore, 1983). Studies of ants in Old World peatlands include those of Gollingwood (1976) in Norway, Gaspar (1966) in Belgium and Vermier (1992) in Switzerland. There have also been several studies of ants in North American peatlands. Francoeur and Pepin (1975, 1978) investigated the density and distribution of Formica dakotensis nests in spruce bogs in Quebec; Kannowski (1959) described the flight activities and colony-founding behavior of ants in Sphagnum bogs in Michigan; and Luken and Billings (1986) studied the effect of two species of ants on hummock dynamics in an Alaskan peat bog. To our knowledge, there have been no published studies of ant-vegetation ecology in North American peatlands.

Pine Butte Fen is a large (450 ha) minerotrophic peatland mosaic of patterned open fen and carr vegetation in N-central Montana (Lesica, 1986). It is a southern outlier of peatland ecosystems that are more common in central and northern Canada (Slack et al., 1980). Colonies of ants are common in the peatland, especially in carr vegetation. The abundance of ants is particularly surprising because the water table is generally within 5 cm of the surface during most of an average year, and flooded conditions are common (McAllister, 1990).

The majority of the ant mounds in Pine Butte Fen are small; however, some are as much as 20 cm high and over 30 cm across [ILLUSTRATION FOR FIGURE 1 OMITTED]. Much of the peatland displays hummock-hollow microtopography with larger shrubs and many species of forbs confined principally to the hummocks (Lesica, 1986; McAllister, 1990). Ants are known to create hummocky microtopography in some meadow systems (Wells et al., 1976; Pavlova, 1977); however, this relationship has not been reported for peatland systems.

In this paper we describe the ant communities associated with different vegetation types in Pine Butte Fen. In addition, we present evidence that ants modify the peatland soil environment, allowing shrubs to become dominant and providing habitat for many species of plants that would otherwise be rare or absent.

STUDY AREA

Pine Butte Fen is located ca. 27 km W of the town of Choteau in Teton County in W-central Montana (47 [degrees] 53[minutes]N, 112 [degrees] 32[minutes]W). The steep front of the main range of the Rocky Mountains is ca. 9 km to the W, and the Teton River flowing from the mountains is 3 km to the N. The peatland occurs at ca. 1400 m elevation on a very gentle SE-facing slope. Water flowing S from the Teton River through permeable glacial till derived from shale and limestone rises to the surface as springs throughout the peatland, providing a nearly constant supply of cold, nutrient-enriched water. Peatland vegetation occurs on peat that is 0.5-3.0 m thick. Upland vegetation surrounding the peatland is Festuca-Agropyron grassland and limber pine (Pinus flexilis) savannah. The Pine Butte Fen is part of The Nature Conservancy's Pine Butte Swamp Preserve.

Mean annual precipitation at Choteau, 25 km to the E, is 289 mm, and mean temperatures for January and July are -6.7 and 19.3 C, respectively (NOAA, 1982). Precipitation is probably somewhat higher and temperatures are lower at the study site.

Vegetation of Pine Butte Fen has been described by Lesica (1986) and McAllister (1990); here we employ the simpler classification provided by Lesica. The peatland is a complex mosaic of open fen, dwarf carr and carr. Open fen vegetation is dominated by brown mosses (Amblystegiaceae) and graminoids with scattered low shrubs, and is most common in the center of the peatland. The surface of the peat displays string and flark patterning (Sjors, 1961), and water is near or above the surface throughout the year. Hummocks, rounded mounds 10-30 cm high, are uncommon and poorly developed. Dwarf carr is dominated by graminoids and mid-height shrubs, and occurs throughout the peatland but is most common near the margins. The surface of the peat is hummocky with shrubs and many species of forbs occurring on the hummocks. Although the peat is generally moist to saturated, and mean depth to water is 5 cm, the water table may be 10-30 cm below the surface at some times of the year (McAllister, 1990). Carr vegetation is dominated by tall shrubs occurring on the abundant hummocks and coarse graminoids in the intervening hollows, and occurs mainly along the margins of the peatland. Mean depth to water is ca. 15 cm (McAllister, 1990).

Many vascular plants, especially broad-leaved species typical of more upland conditions, are confined to hummocks of the carr and dwarf-carr communities in the peatland (Lesica, 1986). Plants considered rare in Montana, such as Cypripedium calceolus, Gentianopsis macounii, and Scirpus pumilus (Lesica and Shelly, 1991), are among those that occur mainly on hummocks (P. Lesica, pers. observ.).

METHODS

Field studies. - We collected data on ant nests at seven study sites in Pine Butte Fen on 20-24 June 1994. Study sites were randomly selected from a gridded aerial photo. At each site we sampled the common vegetation types in subjectively located, representative 50 x 2 m plots. Four carr, four dwarf carr and six open fen plots were sampled. We thoroughly searched each plot and recorded the height, average diameter and species of each ant nest encountered. For each nest we estimated the proportion of bare ground and basal area occupied by vegetation to the nearest 5%. We also estimated canopy cover (Daubenmire, 1959) of vascular plants growing on the nest and the proportion of each nest that was shaded by overhanging shrubs. We made ocular estimates of percent canopy cover to the nearest 5% for dominant vascular plant species in each plot and average height of the tallest shrub stratum to the nearest 10 cm.

We collected soil samples in the dominant vegetation type at each site. Samples were taken from three microtopographic features: (1) level ground; (2) hummocks and (3) Formica nests. Samples were taken from 15 cm-deep profiles, air-dried, and passed through a 2-mm sieve before analysis.

We made observations on the biology of the ant species inhabiting the fen on 26-28 July, 3-4 and 9-11 August, and while surveying the transects 20-24 June. Foraging workers were observed to determine foraging distances and food habits. We noted interactions between ant species and collected samples of homopterous insects that were being attended by ants.

Vascular plant nomenclature follows Hitchcock and Cronquist (1973).

Soil analysis. - The percentage of organic matter was determined from 2-g subsamples by loss on ignition (Nelson and Sommers, 1982). Total nitrogen was determined from 0.5 g subsamples by the Kjeldahl method, and phosphate was determined by the sodium bicarbonate method (Olsen and Sommers, 1982). Analysis of samples for total extractable calcium (Ca), magnesium (Mg), potassium (K) and sodium (Na) was performed with a Jarrell-Ash 865 inductively coupled plasma spectrometer on extracts obtained with 20-ml aliquots of 1.0 N ammonium acetate on 1 g of soil.

Data analysis. - We used Pearson's correlation coefficient to determine which of the following ant nest vegetation characteristics were associated with increasing size of the nests: open soil, basal vegetation cover, and canopy cover of shrubs, Juncus balticus, coarse sedges (Carex aquatilis, C. buxbaumii, C. utriculata), fine sedges (Carex simulata, C. oederi), and Muhlenbergia spp. (M. glomerata and M. richardsonis could not always be distinguished).

The volume of nests was calculated from height (h) and basal radius (r) using the formula for the volume of a hemispheroid when h [less than] r:

Volume = [Pi]h(3[r.sup.2] + [h.sup.2])/6.

When h [greater than] r the mound was regarded as a hemisphere on top of a cylinder, and volume was calculated on that basis (King, 1977a).

The effect of vegetation type on frequency and volume of Formica and Myrmica nests was analyzed with analysis of variance (ANOVA) followed by contrast tests. Frequency and volume were arcsine- and log-transformed, respectively (Sokal and Rohlf, 1981).

Soil samples from the ground, hummocks and Formica nests were collected from within 5 m of each other at each site, and there were appreciable differences in nutrient concentrations among sites. Thus, we used two-way ANOVA without replication followed by contrast tests to analyze the effect of the source of soil on percent organic matter and nutrient concentrations. Site was the random factor, and source of soil was the fixed factor (Sokal and Rohlf, 1981; p. 354-359). Percent organic matter and nitrogen were arcsine-transformed, and concentration of phosphate, calcium, magnesium, potassium and sodium were log-transformed before analyses.

The nonparametric Mann-Whitney test was used to compare shrub canopy cover between Formica and Myrmica nests because the data could not be normalized by transformation.

A level of P [less than or equal to] 0.05 was used to determine statistical significance. Reported probability values are comparison-wise error rates (Stewart-Oaten, 1995).

RESULTS

Vegetation. - Vegetation in the four carr sample plots was dominated by Betula glandulosa and Salix spp. Total shrub cover averaged 74%, and mean height of the B. glandulosa was 2.1 m. Carex aquatilis and Juncus balticus were common ground layer species. Shrub cover averaged 46% in the four dwarf carr plots, and the dominant species were B. glandulosa and Potentilla fruticosa. Mean shrub height was 1.0 m. Juncus balticus was the only consistently important ground layer species. Dominant shrubs in the six open fen plots were also B. glandulosa and P. fruticosa, but mean shrub canopy cover was only 18%, and mean height was 40 cm. Juncus balticus was common in all open fen plots. Carex aquatilis, C. limosa and C. livida were common in half of the open fen plots, and Scirpus acutus was common in the remaining plots.

Ant natural history. - We encountered seven species of ants in Pine Butte Fen (Table 1). Most species formed nests in the well-consolidated and dry peaty soils under shrubs. We found only one colony of Leptothorax muscorum and two of Formica subnuda. Formica podzolica (from here on referred to as Formica) and two species of Myrmica (M. fracticornis and M. incompleta) were the most abundant ant species in number of nests. We did not always distinguish these conspecifics during field work; thus, they will be referred to collectively as Myrmica.
TABLE 1. - Ant species observed at Pine Butte Fen in three plant
community types. Species are classified into four relative abundance
classes: uncommon (U), common (C), abundant (A) and not present (-)

                                   Plant community

Species                 Open fen     Dwarf carr     Carr

Formica podzolica           U            A            A
F. subnuda                  -            U            U
Lasius alienus              -            U            -
L. pallitarsis              -            U            -
Leptothorax muscorum        -            U            -
Myrmica fracticornis        C            U            -
M. incompleta               -            A            C


A typical Formica mound was a dome-shaped structure 12 to 15 cm high and 15 to 20 cm across at ground level. Mounds were composed of well-consolidated blackish-brown organic soil in which the nest chambers of the colony were located. The surface of the mound consisted of 1-4 cm of relatively loose soil particles and plant fragments. Several nest entrances were located on the top and sides of the mound.

Species of Myrmica formed two types of nests. The most conspicuous were mounds of blackish-brown, rather loosely organized soil and plant fragments. They were smaller and more conical-shaped than those of Formica. The largest Myrmica mound observed was 60 cm in diam; chambers and galleries were less firmly formed than those of Formica. The second nest type was subterranean in the peaty soil of hummocks beneath shrubs. Both types of nests usually had one to several small "chimneys" of plant fragments extending above the entrances; these provided a relatively dry environment for brood maturation. A typical chimney was 6 mm in diam and 9 mm high. Mound nests were characteristic of M. fracticornis, whereas M. incompleta was usually found in subterranean nests and only occasionally in mounds.

Workers of Formica foraged on the vegetation over an area ca. 30 to 50 [m.sup.2] around the nest. Workers were rarely observed away from the nests in late June and July. Predation of small arthropods was observed infrequently during this time. In August F. podzolica was commonly found tending aphids, Aphis neogillettei (Aphididae) on Betula glandulosa, Chaitophorus viminalis (Drepanosiphonidae) on Salix spp., and Symydobius sp. (Drepanosiphonidae) on B. glandulosa and Potentilla fruticosa.

Myrmica workers foraged for insects and spiders in the vegetation within 0.5 m of their nests. In addition to this food, workers of M. incompleta tended aphids, including Aphis sp. (Aphididae) on Juncus balticus stems within their nests, and Symydobius sp. (Drepanosiphonidae) on leaves of Potentilla fruiticosa or Betula glandulosa.

Alate reproductives of all ant species found in the fen matured in the colonies in mid-to late summer, and nuptial flights soon followed. Mated female ants that drop to the surface of the open fen community have very limited potential nesting sites. Tufts of the graminoids, Juncus balticus and Scirpus cespitosus, provide slightly elevated sites where females are able to initiate their colonies.

Ant-vegetation relationships. - The density and size of ant nests varied between species and among vegetation types. Formica nests were equally common in carr and dwarf carr vegetation [ILLUSTRATION FOR FIGURE 2A OMITTED]. No Formica nests were encountered in open fen plots, but individuals were occasionally observed in this type of vegetation. Myrmica nests were significantly more common in dwarf carr compared to either carr or open fen vegetation, but density did not differ between these latter two types [ILLUSTRATION FOR FIGURE 2A OMITTED]. Nests of Formica were approximately an order of magnitude larger than those of Myrmica [ILLUSTRATION FOR FIGURE 2B OMITTED]. Formica nests had a mean volume of 18.6 liter and ranged from 0.21 to 80.2 liter, while Myrmica nests ranged from [less than]0.1 to 15.5 liter with a mean of 1.1 liter. Both Formica and Myrmica nests were significantly larger in carr vegetation than in either dwarf carr or open fen [ILLUSTRATION FOR FIGURE 2B OMITTED].

In carr vegetation 23% of Formica nests (N = 30) and 27% of Myrmica nests (N = 29) were built in the open, and the difference between species was not significant ([[Chi].sup.2] = 0.08, P = 0.77). For nests occurring beneath shrubs, mean shrub canopy cover was 27% (SE = 7%) for Formica nests and 51% (SE = 7%) for Myrmica nests, and this difference was statistically significant (Mann-Whitney test, P = 0.006). In dwarf carr 50% of Formica nests (N = 20) and 54% of Myrmica nests (N = 76) were built in the open ([[Chi].sup.2] = 0.03, P = 0.86). For nests occurring beneath shrubs, canopy cover was similar for the two ant species, 22% for Formica nests and 26% for Myrmica nests (Mann-Whitney test, P = 0.98).

Common graminoids on the surface of Formica and Myrmica nests were Juncus balticus, Carex aquatilis, C. buxbaumii and Calamagrostis inexpansa. Muhlenbergia richardsonis and M. glomerata were conspicuous on Formica mounds but were common nowhere else in the peatland. Galium boreale and Triglochin maritima were common forbs on the nests of both species. The strongest correlations with volume of Formica nests were with cover of bare soil (r = 0.26) and canopy cover of Muhlenbergia spp. (r = 0.54); all other variables were only weakly correlated (-0.14 [less than] r [less than] 0.20). No vegetation factors strongly correlated with the volume of Myrmica nests (-0.11 [less than] r [less than] 0.08).

Ant-soil relationships. - Soil was 54%, 61% and 48% organic matter for ground, hummock and Formica mounds respectively, but these differences were not significant (P = 0.15). Concentration of Ca was high throughout the fen but did not differ among positions: 10,615, 12,237 and 11,377 ppm for ground, hummock and mound, respectively (P = 0.33). Mean total N ranged from 1.6-1.8% and did not differ significantly among ground, hummock and Formica mounds (P = 0.45).

Mean concentrations of Mg, P, K and Na were lowest on the ground, highest in Formica mounds and intermediate in hummocks [ILLUSTRATION FOR FIGURE 3 OMITTED]. Ground levels were significantly lower than ant mound concentrations for all four nutrients and significantly lower than hummock soil for P, K and Na [ILLUSTRATION FOR FIGURE 3 OMITTED].

DISCUSSION

Natural history. - Our observations suggest that Formica podzolica workers scavenged and preyed on invertebrates to some extent, but activity was greatest in late summer and early autumn when feeding on aphids and honeydew. Deslippe and Savolainen (1995) found similar feeding behavior for F. podzolica in central Alberta meadows; however, they observed active predatory foraging from early spring through early summer (R. Deslippe, pers. comm.). Workers of Myrmica incompleta also preyed on invertebrates and tended aphids for honeydew, sometimes within their nests.

Formica nests were larger in carr vegetation. Carr has the tallest and densest shrub cover of the three habitats. This greater volume of shrubs likely supports a higher density of shrub-feeding aphids. Myrmica nests were larger in carr vegetation but were more than twice as dense in the dwarf carr. We know of no resource-related explanation for the greater density of Myrmica nests in dwarf carr. However, in carr vegetation Formica nests occupied less shaded locations than Myrmica nests, but in the sunnier dwarf carr habitat, there was no difference in nest-shading between the species. These results suggest that there may be competition for sunny nest sites in carr, resulting in a lower density (but not volume) of nests for the smaller and presumably subordinate species. Thermoregulation is thought to be a main function of ant mounds, and many ant colonies depend on solar heat to produce sexual forms (Petal, 1978; see review in Holldobler and Wilson, 1990, p. 373). Both Formica and Myrmica were rare in open fen vegetation, undoubtedly due to the difficulty associated with founding a colony in soil where water is at or above the surface throughout the year.

Ant-vegetation interactions. - The percentage of organic matter and concentration of Ca and total N in soils from the ground, hummocks and Formica mounds did not differ significantly in Pine Butte Fen. However, Mg, P, K and Na in ant mounds were significantly higher than ground levels. Although elevated levels of N may occur in mounds of some ant species (Czerwinski et al., 1971), there is often no significant difference (Wells et al., 1976; King, 1977b; Culver and Beattie, 1983), probably because of high mineralization rates. Higher levels of P[O.sub.4] - and K are frequently reported for ant mounds in meadow systems (Czerwinski et al., 1971; Gentry and Stiritz, 1972; Wells et al., 1976; King, 1977b; Petal, 1978; Culver and Beattie, 1983). The low mobility of P[O.sub.4] - in calcareous soils (Cole et al., 1963) and the high concentrations of K in phloem sap fed on by aphids (Woodwell and King, 1991) probably explain the enhancement of these two nutrients in mound soils. Enhanced levels of Na and Mg have also been reported for some ant mounds (Petal, 1978).

The presence of higher levels of P, Na and K in both hummock and ant mound soil compared to the adjacent ground provides evidence that hummocks are abandoned Formica mounds. Formica podzolica can construct nests on cold, wet soil that is not innundated, and it is unlikely that Formica nests are converted from existing hummocks because in other habitats F. podzolica build nests de novo rather than occupying existing mounds (R. DeSlippe, pers. comm.). Hummock-hollow microtopography is common in peatlands throughout the boreal zone, and differential growth rate of Sphagnum mosses is most commonly invoked to explain these patterns (Moore and Bellamy, 1974; Johnson, 1985). However, Sphagnum spp. are absent at Pine Butte Fen (Lesica, 1986). Other processes, such as tussock-forming by graminoids and freeze-thaw cycles (Moore and Bellamy, 1974; Johnson, 1985), may be contributing to the hummock-hollow topography in this peatland, possibly by providing drier sites for ants to initiate nests, but there is no evidence to suggest that they are responsible for the common, large hummocks.

Our results indicate that ants increase available nutrient supplies in ant mounds and subsequently in hummock soils in Pine Butte Fen. In addition, hummock soils are higher above the water table, undoubtedly providing better aeration and warmer temperatures during the early portion of the growing season. Ant mound soils generally have lower bulk density than the surrounding ground (Wali and Kannowski, 1975; King, 1977b). These beneficial changes to the soil can significantly affect the vegetation of a site because ant colonies may build new mounds frequently, thus altering large quantifies of soil (King and Sallee, 1956; Czerwinski et al., 1971; Gentry and Stiritz, 1972; but see King, 1977a).

The activities of ants have a profound effect on the peatland vegetation of Pine Butte Fen. While only a small number of specialized vascular plant species are adapted to the cold, anoxic, peatland surface, ant activity provides habitat for numerous nonhydric species. Permanent water is at or very near the surface in most peatland systems, and a change of only a few centimeters in elevation can result in a shift of vegetation (Jeglum, 1971; Damman and Dowhan, 1981; Karlin and Bliss, 1984). An ant mound or hummock, although only 10-20 cm above the surface, provides a warm, well-aerated environment, radically different from the surrounding matrix. Active Formica mounds often develop a distinctive cover of the strongly rhizomatous grasses Muhlenbergia richardsonis and M. glomerata as they become older and larger [ILLUSTRATION FOR FIGURE 1 OMITTED]. Enhanced nutrient levels present in active mounds decline gradually but remain higher than adjacent ground for long periods (Czerwinski et al., 1971). Once the nests have been abandoned, they provide habitat for a different assemblage of plant species more typical of drier and/or warmer conditions (Lesica, 1986). Although shrubs occur on the peatland surface, they are larger and more frequent on hummocks (P. Lesica, pers. observ.), probably due to better aeration.

Changes in soil chemical and physical properties and floristic composition have also been reported for ant mounds in meadow systems (Beattie and Culver, 1977; King, 1977b; Petal, 1978; Rissing, 1986; Culver and Beattie, 1986). Here too, strongly rhizomatous plants are often the main colonizers of active mounds (King, 1977a, 1977b; Petal, 1978). However, the distinctive plant composition of meadow ant mounds quickly reverts to zonal vegetation shortly after mounds are abandoned (Wells et al., 1976; King, 1977a). Unlike meadow systems, the presence of abandoned ant mounds in peatland vegetation at Pine Butte Fen appears to greatly alter the structure and composition of vegetation over the long term because the mounds provide a much steeper moisture gradient in the wet environment.

It is interesting to speculate on the long-term dynamics of the ant-vegetation system at Pine Butte Swamp. Formica podzolica colonies in Pine Butte Fen and elsewhere (DeSlippe and Savolainen, 1995) obtain much of their nutrition from aphids feeding on shrubs. Abandoned nests provide additional habitat for shrubs that, in turn, furnish more feeding sites for aphids. The result may be larger aphid populations providing more nutrition for ants, leading to greater ant densities. Factors other than aphid density, such as availability of insect prey or nest sites, may be limiting Formica abundance. Nonetheless, the ant-shrubaphid positive feedback relationship could be one force driving the vegetation dynamics in the dwarf carr and carr communities.

Ants are abundant in most ecosystems, and their effects on vegetation are well-documented (Petal, 1978; Woodell and King, 1991). Nonetheless, we are not aware of any previous reports of ants creating hummock-hollow microtopography in peatlands, although ants in the genus Formica have been implicated in the retrogression of hummocks in an Alaskan Sphagnum bog (Luken and Billings, 1986). Furthermore, we know of no reports in which ants have been shown to influence the structure and composition of long-term vegetation communities as greatly as at Pine Butte Fen. Other processes, such as tussock-forming by graminoids (Johnson, 1985), may be contributing to the hummock-hollow topography in this peatland, but we believe that none are as important as nest-building by ants. Brown mosses dominate many other peatlands in southern Canada and northern United States (Slack et al., 1980; Janssens and Glaser, 1984). Formica mounds do occur in peatland systems in Colorado (A. Carpenter, The Nature Conservancy; pers. comm.) and NW Montana (P. Lesica, pers. observ.). Further research is required to determine the importance of ants in microtopographic processes in other rich fens throughout North America and Eurasia.

Acknowledgments. - We are grateful to Kana Moll for making observations on feeding. David Carr, David Hanna, Kana Moll, Jennifer Grabon and Rebecca Kruger assisted with field work. Steve Baker and Johnnie Moore conducted the soil analyses. We are grateful to Mike Chessin for translation from the Russian and to Stefan Cover for identifying ant specimens. Richard DeSlippe and an anonymous reviewer commented on an earlier draft of the manuscript. Funding was provided by The Nature Conservancy's Pine Butte Swamp Preserve.

LITERATURE CITED

BEATTIE, A. J. AND D. C. CULVER. 1977. Effects of the mound nests of the ant, Formica obscuripes, on the surrounding vegetation. Am. Midl. Nat., 97:390-399.

COLE, C. V., S. R. OLSEN AND C. O. SCOTT. 1963. The nature of phosphate adsorption by calcium carbonate. Soil Sci. Soc. Am. Proc., 17:352-356.

COLLINGWOOD, C. A. 1976. Mire invertebrate fauna at Eidskog, Norway. III. Formicidae (Hymenoptera, Aculeata). Norw. J. Entomol., 23:185-187.

CULVER, D. C. AND A. J. BEATTIE. 1983. Effects of ant mounds on soil chemistry and vegetation patterns in a Colorado montane meadow. Ecology, 64:485-492.

CZERWINSKI, Z., H. JAKUBCZYK AND J. PETAL. 1971. Influence of ant hills on the meadow soils. Pedobiologia, 11:277-285.

DAMMAN, A. W. AND J. J. DOWHAN. 1981. Vegetation and habitat conditions in Western Head Bog, a southern Nova Scotia plateau bog. Can. J. Bot., 59:1343-1359.

DAUBENMIRE, R. 1959. A canopy-coverage method of vegetational analysis. Northwest Sci., 33:43-64.

DAVIDSON, D. W., J. H. BROWN AND R. S. INOUYE. 1980. Competition and the structure of granivore communities. BioScience, 30:233-238.

DESLIPPE, R. J. AND R. SAVOLAINEN. 1995. Sex investment in a social insect: the proximate role of food. Ecology, 76:375-382.

FRANCOEUR, A. AND D. PEPIN. 1975. Productivite de la fourmi (Formica dakotensis dans la pessiere tourbeuse. I. Densite observee et densite estimee les colonies. Insectes Soc., 22:135-150.

----- AND -----. 1978. Productivite de la fourmi (Formica dakotensis dans la pessiere tourbeuse. II. Variations annuelles de la densite des colonies de l'occupation des nids et de la repartition spatiale. Insectes Soc., 25:13-30.

GASPAR, C. 1966. Etude myrmecologique des tourbieres dans les Hautes-Fagnes en Belgique (Hymenoptera, Formicidae). Rev. Ecol. Biol. Sol., 3:301-312.

GENTRY, J. B. AND K. L. STIRITZ. 1972. The role of the Florida harvester ant, Pogonomyrmex badius, in old field mineral nutrient relationships. Environ. Entomol, 1:39-41.

GORE, A. J. P. (ED.). 1983. Ecosystems of the world 4A. Mires: swamp, bog, fen and moor. Elsevier Scientific Publishing Company, Amsterdam. 440 p.

HANDEL, S. N., S. B. FISCH AND G. E. SCHATZ. 1981. Ants disperse a majority of herbs in a mesic forest community in New York State. Bull. Torrey Bot. Club, 108:430-437.

HITCHCOCK, C. L. AND A. CRONQUIST. 1973. Flora of the Pacific Northwest. University of Washington Press, Seattle. 730 p.

HOLLDOBLER, B. AND E. O. WILSON. 1990. The ants. Harvard University Press, Cambridge, Mass. 732 p.

HUXLEY, C. R. 1980. Symbiosis between ants and epiphytes. Biol. Rev. (Camb.), 55:321-340.

JANSSENS, J. A. AND P. H. GLASER. 1984. The bryophyte flora and major peat-forming mosses at Red Lake Peatland, Minnesota. Can. J. Bot., 64:427-442.

JEGLUM, J. K. 1971. Plant indicators of pH and water level in peatlands at Candle Lake, Saskatchewan. Can. J. Bot., 49:1661-1676.

JOHNSON, C. W. 1985. Bogs of the Northeast. University Press of New England, Hanover, N.H. 269 p.

KANNOWSKI, P. B. 1959. The flight activities and colony-founding behavior of bog ants in southeastern Michigan Insectes Soc., 6:115-162.

KARLIN, E. F. AND L. C. BLISS. 1984. Variation in substrate chemistry along microtopographical and water-chemistry gradients in peatlands. Can. J. Bot., 62:142-153.

KING, R. L. AND R. M. SALLEE. 1956. On the half-life of nests of Formica obscuripes Forel. Proc. Iowa Acad Sci., 63:721-723.

KING, T. J. 1977a. The plant ecology of ant-hills in calcareous grasslands. II. Succession on the mounds. J. Ecol., 65:257-278.

-----. 1977b. The plant ecology of ant-hills in calcareous grasslands. I. Patterns of species in relation to ant-hills in southern England J. Ecol., 65:235-256.

LESICA, P. 1986. Vegetation and flora of Pine Butte Fen, Teton County, Montana Great Basin Nat., 46:22-32.

----- AND S. J. SHELLY. 1991. Sensitive, threatened and endangered vascular plants of Montana. Montana Nat. Heritage Program Occas. Publ. No. 1. Helena, Montana. 88 p.

LUKEN, J. O. AND W. D. BILLINGS. 1986. Hummock-dwelling ants and the cycling of microtopography in an Alaskan peatland. Can. Field-Nat., 100:69-73.

LYFORD, W. H. 1963. Importance of ants to brown podzolic soil genesis in New England. Harvard For. Pap. No. 7. Petersham, Mass. 18 p.

MCALLISTER, D. C. 1990. Plant community development in a minerotrophic peatland, Teton County, Montana. Ph.D. Diss., School of Forestry, University of Montana, Missoula. 152 p.

MOORE, P. D. AND D. J. BELLAMY. 1974. Peatlands. Springer-Verlag, New York. 220 p.

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION (NOAA). 1982. Monthly normals of temperature, precipitation and heating and cooling degree days. Montana, 1950-1980. National Climatic Center, Ashville, N.C.

NELSON, D. W. AND L. E. SOMMERS. 1982. Total carbon, organic carbon and organic matter, p. 539-580. In: A. L. Page, R. H. Miller and D. R. Keeney (eds.). Methods of soil analysis, Part 2. American Society of Agronomists, Madison, Wis.

OLSEN, S. R. AND L. E. SOMMERS. 1982. Phosphorus, p. 403-430. In: A. L. Page, R. H. Miller and D. R. Keeney (eds.). Methods of soil analysis, Part 2. American Society of Agronomists, Madison, Wis.

PAVLOVA, Z. F. 1977. Microstructure of the biogeocoenoses of coastal lake shores. Ekologiia, 5:62-71.

PETAL, J. 1978. The role of ants in ecosystems, p. 293-325. In: M. V. Brian (ed.). Production ecology of ants and termites. Cambridge University Press, London.

RISSING, S. W. 1986. Indirect effects of granivory by harvester ants: plant species composition and reproductive increase near ant nests. Oecologia, 68:231-234.

SJORS, H. 1961. Surface patterns in boreal peatland. Endeavor, 20:217-224.

SLACK, N. G., D. H. VITT AND D. G. NORTON. 1980. Vegetation gradients of minerotrophically rich fens in western Alberta. Can. J. Bot., 58:330-350.

SOKAL, R. AND F. J. ROHLF. 1981. Biometry. W. H. Freeman and Company, San Francisco. 859 p.

STEWART-OATEN, A. 1995. Rules and judgements in statistics: three examples. Ecology, 76:2001-2009.

VERMIER, R. 1992. Recherche ecofaunistique sur les fourmis du genre Formica L. de la tourbiere du Cachot (Jura Neuchatelois) et haut marais voisines (Hymenoptera, Formicidae). I. Liste des especies et leurs biotpoes preferentiels. Bull. Soc. Neuchatel. Sci. Nat. 115:61-82.

WALI, M. K. AND P. B. KANNOWSKI. 1975. Prairie ant mound ecology: interrelationships of microclimate, soils and vegetation, p. 155-169. In: M. K. Wali (ed.). Prairie: a multiple view. University of North Dakota Press, Grand Forks.

WELLS, T. C. E., J. SHEAIL, D. F. BALL AND L. K. WARD. 1976. Ecological studies on the Porton Ranges: relationships between vegetation, soils and land-use history. J. Ecol., 64:589-626.

WOODWELL, S. R. J. AND T. J. KING. 1991. The influence of mound-building ants on British lowland vegetation, p. 521-535. In: C. R. Huxley and D. F. Cutler (eds.). Ant-plant interactions. Oxford University Press, Oxford.
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Author:Lesica, Peter; Kannowski, Paul B.
Publication:The American Midland Naturalist
Date:Jan 1, 1998
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