Community Structure II
Presiding: R Brenes, Southern Illinois University; T Heatherly, Southern Illinois University
NB32B-01 10:30h
Spatial and Temporal Variation in Tadpole Communities in Neotropical Montane Streams.
Tadpoles transfer nutrients and energy between environments and amphibian declines are likely to affect this process. As the first step in determining amphibian production, we quantified seasonal and microhabitat variation in abundance and diversity of tadpoles at two sites: pre and post-decline. We quantified density of all tadpole species in riffles, runs, and pools monthly for a year. Three species occurred at the decline site (average density = 0.0026 ± 0.0034 m-2), and 10 of 11 species occurred year-round at the healthy site (2.80 ± 4.37 m-2). Tadpole abundance varied seasonally, with more tadpoles (X2=270.23, 10 d.f., p<0.001) at lower densities (0.50 m-2 ± 0.58) during the rainy season than during the dry season (5.10 m-2 ± 5.31; t = 3.079, 10 d.f., P= 0.01). Microhabitats differed in overall density (leaf packs, 1.044 ± 1.17 m-2; riffles, 0.04 ± 0.013 m-2, pools 0.38 ± 0.005 m-2; isolated pools 2.09 ± 1.03 m-2). Riffles and pools had a diverse tadpole assemblage, but leaf packs and isolated pools were dominated by Hyalinobatrachium colymbiphyllum (3.74 ± 1.86 m-2, F= 13.47, p=0.01) and Colostethus flotator (9.35 ± 4.56 m-2, F=32.77, p=0.002), respectively. High abundance, density, prevalence, and persistence suggest an important role for tadpoles in these ecosystems.
http://www.science.siu.edu/zoology/gradstudents/brenes/index.html
NB32B-02 10:45h
Influence of Thermal Regime on Mayfly Assemblages in Mountain Streams
Theory predicts that thermal regime is an important factor regulating aquatic insect assemblages. Small affordable temperature loggers now make possible accurate measurements of thermal regime throughout a river basin. I measured the summer thermal regime at stream sites in the Sawtooth Mountains of Idaho and collected quantitative samples of benthic macroinvertebrates at the same sites. Sites were chosen below lakes as well as in streams without lakes to increase the variation in thermal regimes. Ordination and multiple regression were used to explain the variation in mayfly assemblages. Maximum temperature explained the largest percentage of the variation in assemblages.
NB32B-03 11:00h
Stream insect distributional patterns and metapopulation models: effects of spatial scale and sampling intensities
Understanding patterns of distribution of organisms and factors underlying them is a fundamental goal of ecology. We used stream insect datasets from Alabama, Alaska, Maine, Maryland, New York, and the northwest Pacific Coast to examine occupancy-frequency patterns and to assess the effects of changing spatial scales and sampling intensities (number of sites) on these patterns. Differences in proportions of satellite taxa (those occurring in <10% of sites) and core taxa (occurring in >90% of sites) contributed to differences in modality in occupancy-frequency patterns. Core taxa were usually widespread and speciose genera. Cases where satellite taxa dominated community structure, which was often, tended to show unimodal occupancy-frequency patterns. Cases where core taxa contributed substantially to richness tended to show bimodal patterns. Proportions of core taxa decreased with increasing spatial scales and sampling intensities. Proportions of satellite taxa increased with spatial scale, and showed positive log relationships with sampling intensity (r2 = 0.74 - 0.96). There was also a pattern of increasing proportions of core taxa with decreasing latitude (r2 = 0.92, P = 0.01). Results indicate that spatial scale and sampling intensity influence occupancy-frequency patterns of stream insects and may thus influence interpretation of metapopulation models when applied to these systems.
NB32B-04 11:15h
Assemblages of Dragonfly Species that Emerged from Small Wetlands Along an Urbanization Gradient Within the State of Rhode Island, from May to October 2004.
Dragonfly exuviae were collected during six visits to 21 small wetlands, from mid-May through mid-October 2004. The 21 palustrine wetlands range from highly anthropogenic sites in greater Providence, to small, natural ponds in rural Rhode Island. Exuviae were identified to species in the laboratory. Dragonfly communities are analyzed for assemblage patterns. Land-use in surrounding wetland buffers, along with water quality measurements, are evaluated for landscape and environmental factors which affect species distributions.
NB32B-05 11:30h
Looking for Evidence of Neutral Processes in Rocky Mountain Alpine Stream Communities: a Novel Approach Using Population Genetics
We used alpine stream communities in the Rocky Mountain National Park area, Colorado, for a novel test of neutral community theory borrowing concepts from the neutral theory of molecular evolution. High beta diversity driven by low dispersal among sites (both prominent features of alpine streams) is a key tenet of neutral theory, under which ecological drift is analogous to genetic drift, and distance decay corresponds to genetic isolation by distance. Hence, our expectation was that, under neutral theory, patterns of community structure ought to mimic patterns of neutral population genetic structure of a representative local species. Treating species as "alleles," we analyzed variation in community structure among five local communities using analysis of molecular variance (AMOVA); we used the same method to analyze population genetic structure of a common alpine blackfly (Prosimulium neomacropyga) occupying the same sites. Both communities and populations exhibited significant structure among sites (FST = 0.265 and 0.233, respectively); however, a Mantel test revealed no correlation between pairwise distances at the community and the population levels. Although neutral processes may be important in structuring alpine stream communities, rates of drift may vary significantly between levels of organization, and other factors such as environmental heterogeneity are also influential.
NB32B-06 11:45h
Persistence of Macroinvertebrate Communities in Reference Streams of Denali National Park, Alaska.
Macroinvertebrates were collected from riffles in six reference streams in Denali National Park and Preserve, Alaska every year from 1994 to 2001. Two of the streams were also sampled in 2002. The most persistent taxon was Baetis, but its abundance varied markedly from year to year, ranging from < 50 m-2 to nearly 2000 m-2. Rank abundance of the 10 most abundant members of the macroinvertebrate community (including and excluding Chironomidae) showed significant concordance over time using Kendall's W. Using Jaccard's Coefficient of Similarity, assemblage persistence was found to be highest in streams with greater channel stability and lower flow variability. Spearman's coefficients of rank abundance between years were significantly lower when snowfall was high, indicating the potential effects of spring runoff on persistence. Due to the marked variation in abundance and lack of persistence of individual taxa, a number of biotic ratio metrics (e.g. EPT/Total individuals, % Chironomidae), varied almost across their entire range in these unimpaired streams, making these metrics inappropriate for biomonitoring at higher latitudes. The lack of persistence of individual taxa may also have implications for biomonitoring using predictive models.e to the marked variation in abundance and lack of persistence of individual taxa, a number of biotic ratio metrics (e.g. EPT/Total individuals, % Chironomidae), varied almost across their entire range in these unimpaired streams, making these metrics inappropriate for biomonitoring at higher latitudes. The lack of persistence of individual taxa may also have implications for biomonitoring using predictive models.