The role of habitat and dispersal in shaping the biodiversity of riverine insect assemblages

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University of New Brunswick


Given limited resources, biomonitoring progrrum are touted as a source of biodiversity information for conservation planning in riverine ecosystes. However, the degree to which patterns revealed by biomonitoring are reflected in unsampled mesohabitats and undersampled taxonomic groups has not been fully addressed. Differences in dispersal capacity among taxonomic groups, in particular, may result in divergent patterns of biodiversity at landscape and regional scales. I sought to address the suitability of biological monitoring data in freshwater biodiversity assessment, and to test the prediction that the degree of spatial structuring in aquatic insect assemblages is inversely related to their dispersal capacity. My thesis comprises four articles. The first addresses whether macroinvertebrate biodiversity patterns in riffles, the target mesohabitat of Canada's national aquatic biomonitoring program, are reflective of those in riverine wetlands. The second addresses whether biodiversity in a group of insects that is abundant in biomonitoring samples (Trichoptera) reflects that of an underrepresented group (Odonata). The third tests the above prediction by comparing the degree of spatial structuring in the weakly dispersing Trichoptera and the stronger dispersing Odonata. The final article investigates regional and national aquatic insect biodiversity patterns utilizing the national biomonitoring dataset, and seeks to evaluate the influence of scale on the observation of spatial structuring aquatic insect assemblages. Several key findings emerged from this work: 1) Patterns of invertebrate taxon richness and beta diversity in riftles poorly reflect those in riverine wetlands. 2) Odonata and Trichoptera biodiversity were not always congruent, however, differences in abundance among groups may account for weak correlations. 3) Both Odonata and Trichoptera assemblages demonstrate relatively weak spatial structuring at a landscape (ie. 5th order catchment) scale. The weak explanatory ability of spatial variables was also apparent at a regional scale, as just one of the Water Survey of Canada sub drainages within the Pacific drainage demonstrated a significant spatial component in aquatic insect assemblage variation These findings suggest caution in the application of biomonitoring data to conservation planning. Although landscape and regional scale structuring of aquatic insect communities may be weak, it does not preclude the existence of smaller scale spatial structuring driven by local dispersal processes.