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Do semi-arid landscapes in the American Southwest cause discrete communities of caddisflies (trichoptera) in streams?

Expansive semi-arid landscapes in the Lower Colorado River Basin in the American Southwest limit ability of aquatic organisms to disperse from one region to another Distances between drainages are typically >100 km. In addition, connectivity of streams is disjointed by intensive farming and grazing, all of which contribute to increased embeddedness of channels, secondary salinization, and reduce canopy cover (Blinn and Poff, 2005), and many landscapes are interrupted by a series of dams. The long-term drought predicted for the American Southwest (Seager et al., 2007) and continued use of watersheds by agricultural practices will continue to decrease connectivity between streams. We examined assemblages of caddisflies from 93 sites on streams during summers (May-September) of 2003 and 2004 to test whether a priori defined regions have discrete communities of caddisflies across the semi-arid landscape of the Lower Colorado River Basin, and to determine which species make the greatest contribution to assemblages in these discrete communities.

There are four large drainages (Lower Colorado River, Little Colorado River, Salt River, Gila River) in the Lower Colorado River Basin. The basin includes nearly 300,000 [km.sup.2] with elevations from <50 to >3,700 m. Average annual precipitation is <11 cm; 65 cm in higher elevations and <7 cm in lower elevations (Blinn and Poff, 2005). Temperatures in summer are >45[degrees]C in low deserts with annual evapotranspiration approaching 200 cm. Thus, many streams at lower elevations are intermittent.

We established seven a priori designations of regions throughout the Lower Colorado River Basin following Blinn and Ruiter (2006). These regions were restricted to isolated areas between arid landscapes including three large deserts. The seven regions included are as follows: 1) White Mountains in eastern Arizona, high elevation >2,000 m; 2) Chiricahua Mountains in southeastern Arizona, high elevation 1,600-2,000 m; 3) Verde Valley drainage in north-central Arizona, moderate to high elevation 975-1,830 m; 4) Colorado River drainage; 5) Utah-Arizona border; 6) western Arizona; and 7) southern Arizona. All regions are separated by [greater than or equal to] 75 km, across arid to semi-arid landscapes (Table 1).

We used the ANOSIM similarity statistical method to analyze data from adult specimens to calculate relative abundance of species and to test for differences between regional assemblages of caddisflies (Clarke, 1993). This procedure tests for significant groupings of communities by comparing within-group distances to among-group distances of 999 sets of randomly assigned groups to the original a priori grouping. Additionally, we conducted a hierarchical cluster analysis based on rank-similarities of the same data to illustrate our groupings. We also conducted an analysis of which species contributed to the uniqueness of each group and their average relative abundance. This analysis was conducted using the SIMPER routine of PRIMER version 5 (Clarke and Gorley, 2001), which tests for contributions of each species to overall dissimilarity among groups of data. Species or assemblages of species, which contribute to a high percentage of dissimilarity among groups of samples, can be used as indicators for those groups.

Some significant differences between communities of caddisflies among the seven regions were detected. Pairwise ANOSIM comparisons of assemblages of adult caddisflies among seven regional groups in Lower Colorado River Basin are presented in Table 1. Paired assemblages of the White Mountains, Verde Valley, Colorado River, Utah-Arizona border, western Arizona, and southern Arizona were most different from other regional assemblages. Pairwise comparisons showed the assemblage at Utah-Arizona border was significantly different from only the assemblage in the White Mountains, possibly due to the limited number of sites (n = 3) at the Utah-Arizona border. The assemblage in the Colorado River was significantly different from all other assemblages except the Utah-Arizona border. The highly regulated flows in the Colorado River likely are responsible for these differences. Therefore, the lowland desert regions are more similar to each other, and the two cold-water mountain regions are similar (White Mountains and Chiricahua Mountains), but the Verde Valley and Colorado River stand out as being different. The fewer significant correlations between the Utah-Arizona border and southern-Arizona groupings with other groupings may have resulted from the reduced number of sites due to high aridity in these areas.

A hierarchical cluster analysis based on rank-similarities showed clusters of various regions (Fig. 1). Sites in the White Mountains (group 1) clustered primarily on the top of the dendrogram, sites in the Chiricahua Mountains (group 2) are in the center, and assemblages of caddisflies in western and southern Arizona (groups 6 and 7) generally are assembled on the bottom of the dendrogram. Other regions are less well defined, but had patterns of within-region clustering across the dendrogram. For example, sites within Verde Valley (group 3) are across a relatively broad range of elevations (975-1,830 m) and environmental variables within Verde Valley are varied (Blinn and Ruiter, 2006).

Species of caddisflies that contributed to uniqueness of each assemblage in each group and their average relative abundances are in Table 2. These groups included >80% of species in each assemblage. Only nine of the 24 species that contributed to the seven assemblages were present in >1 group (Table 2). These included Cheumatopsyche arizonensis, Cheumatopsyche pinula, Helicopsyche borealis, Hydropsyche auricolor, Hydropsyche occidentalis, Hydroptila ajax, Hydroptila arctia, Neotrichia okopa, and Ochrotrichia dactyophora. This suggests that these species have broad ranges of tolerance.

Athough high-elevation assemblages have similar conditions in streams and are [less than or equal to] 175 km apart, they have different assemblages. Only two (C. arizonensis and O. dactyophora) of the combined 18 species (<17%) were common in assemblages from high elevations (1,600-2,797 m). Blinn and Ruiter (2005) reported streams in groups 1 and 2 have high riparian cover, and low temperature of water, embeddedness of channels, and specific conductance. Connectivity of streams between these groups is limited, as the San Simon Wash-Upper Gila River drains the Chiricahua Mountains and the Upper Gila River, Salt River, and Little Colorado River drain the White Mountains.

Assemblages in groups 1 and 2 are separated by the Chihuahuan Desert, group 3 is separated from group 2 by the Sonoran Desert, and assemblages in group 1 are separated by shrublands of the Colorado Plateau (Ricketts et al., 1999). All of these terrestrial ecoregions are modified by intensive ranching and farming, which have contributed to reduced and intermittent flows with dry channels in some instances (Blinn and Poff, 2005). Only three of the 13 species (H. arctia, H. ajax, Neotrichia okopa) in the low-elevation assemblages were common to all three of these groups. Groups 4, 5, 6, and 7 have low riparian cover and high temperatures of water, embeddedness of channels, and specific conductance, and generally are considered to be lowland-desert streams (Blinn and Ruiter, 2005).

We hypothesize that the intensively used, semi-arid landscapes in the Lower Colorado River Basin have increased genetic drift and, therefore, reduced potential for recombination in caddisflies with weak capabilities of flight (Jackson and Resh, 1989; Miller et al., 2002; Finn and Poff, 2008). Other aquatic organisms in the Lower Colorado River Basin with limited dispersal or restricted by limited connectivity of streams also have high genetic diversity that is not apparent from morphological comparisons. Thomas et al. (1997, 1998) proposed that xeric landscapes in Arizona promoted genetic divergence in populations of amphipods, and Govedich et al. (1999) discovered that populations of leeches were isolated with significant differentiation among populations. Both amphipods and leeches have limited dispersal abilities. In addition, Greenberg (1999) elucidated reduced combinations in Little Colorado River spinedace (Lepidomeda vittata) along the ephemeral Little Colorado River in the arid landscape of Arizona.

Sites and Willig (2000) suggested genetic drift and reduced genetic recombinations have occurred in the water bug, Ambrysus mormon, in isolated springs along now-dry sections of the White River, Nevada. Many of the springs that supplied the river with water are now used for irrigation. Morphometrics of species in springs along dry sections of the White River and those still connected are quite different, yet all are considered to be A. mormon. More recently, Zickovich and Bohonak (2007) compared genetic diversity ofpopulations ofthe amphipod, Hyalella azteca, in perennial and intermittent streams in the semiarid region of southern California. Genetic divergence between perennial sites was not significantly different, but populations along extended intermittent sections were significantly different.

Jansen (1967) proposed the importance of cold temperatures on high mountains in the tropics as barriers to movement of plants and animals. Aridity coupled with intensive agricultural practices may provide a similar barrier in the American Southwest.

Funds were provided to DWB in part by the Arizona Regents' Professor Program at Northern Arizona University.

Submitted 5 March 2010. Accepted 12 June 2011. Associate Editor was Joseph P. Shannon.


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Dean W. Blinn, * David E. Ruiter, and Allen Haden

Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011 (DWB) 6260 South Grant Street, Centennial, CO 80121 (DER)

Natural Channel Design, Inc., 206 South Elden Street, Flagstaff, AZ 86001 (AH)

* Correspondent:
TABLE 1--Pairwise comparisons of communities of adult caddisflies
among seven a priori regional groups in Arizona. Distance (km) between
regions are listed and ANOSIM R-values and significant pairwise
differences ([less than or equal to] 5%) are noted (*). Bonferroni
adjusted = 0.24%, indicating significant pairwise comparisons at a
conservative alpha level.

                         2 Chiricahua   3 Verde    4 Colorado   5 Utah-
    Regional group        Mountains      Valley      River      Arizona

1 White Mountains        175            200        425          325
                           0.157          0.284      0.383        0.470
                          12.2            0.1 *      0.1 *        0.8 *
2 Chiricahua Mountains                  350        550          575
                                          0.045      0.426        0.405
                                         33.9        0.3 *        5.4
3 Verde Valley                                     200          200
                                                     0.176        0.119
                                                     3.6 *       78.5
4 Colorado River                                                100
5 Utah-Arizona

6 Western Arizona

                         6 Western   7 Southern
    Regional group        Arizona     Arizona

1 White Mountains        400         150
                           0.701       0.471
                           0.1 *       0.1 *
2 Chiricahua Mountains   475         175
                           0.293       0.040
                           1.8 *       5.62
3 Verde Valley           300         300
                           0.412       0.220
                           0.1 *       1.1 *
4 Colorado River         100         325
                           0.545       0.211
                           0.1 *       2.4 *
5 Utah-Arizona           175         350
                          -0.075      -0.218
                          65.5        91.5
6 Western Arizona                     75

TABLE 2--Percentage contribution ([greater than or equal to] 80%)
of species of caddisflies to regional groupings of sites in Arizona.
Species with high percentages contributed most to identity of the

                                     Contribution   Average relative
          Group and taxa                 (%)         abundance (%)

1 White Mountains,
  high elevation
  Ceratopsyche oslari                    29.0              11
  Atopsyche sperryi                      17.6               6
  Hydropsyche auricolor                  11.4               7
  Ochrotrichia dactylophora               5.9               7
  Polycentropus arizonensis               4.9               4
  Hesperophylax occidentalis              4.8               6
  Cheumatopsyche arizonensis              3.3               5
  Oecetis disjuncta                       3.1               3
  Cheumatopsyche pinula                   2.4               6
  Hydropsyche occidentalis                1.8               3
  Gumaga griseola                         1.8               4
2 Chiricahua Mountains,
  high elevation
  Ochrotrichia dactylophora              31.1              24
  Cheumatopsyche arizonensis             29.8              20
  Hydroptila arctia                      22.4              13
  Wormaldia arizonensis                   6.2              10
  Hydroptila rono                         3.6               8
3 Verde Valley, high elevation
  Hydroptila arctia                      29.6              16
  Cheumatopsyche arizonensis             12.7               7
  Hydroptila ajax                        10.3               9
  Hydropsyche occidentalis                8.0               6
  Chimarra utahensis                      6.9               5
  Helicopsyche borealis                   5.0               4
  Hydropsyche auricolor                   4.8               5
  Cheumatopsyche pinula                   3.5               4
4 Colorado River, low elevation
  Hydroptila arctia                      73.1              42
  Ochrotrichia logana                    16.4              21
  Ochrotrichia lomenta                    8.3              20
5 Utah-Arizona,
  low elevation
  Hydroptila ajax                        54.8              21
  Hydroptila arctia                      41.4              32
6 Eastern Arizona, low elevation
  Hydroptila ajax                        24.7              18
  Hydroptila icona                       23.2              20
  Smicridea fasciatella                  16.4               8
  Oxyethira arizona                      11.3              16
  Helicopsyche borealis                   6.5               5
  Neotrichia okopa                        6.4               5
7 Southern Arizona,
  low elevation
  Neotrichia okopa                       41.4              21
  Hydroptila arctia                      23.2              12
  Culoptila cantha                        9.1              10
  Hydropsyche auricolor                   4.9               7
  Hydropsyche occidentalis                4.8               9
  Hydroptila ajax                         4.1               2
  Cheumatopsyche arizonensis              3.6               3
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Author:Blinn, Dean W.; Ruiter, David E.; Haden, Allen
Publication:Southwestern Naturalist
Article Type:Report
Geographic Code:1USA
Date:Mar 1, 2012
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