Macroinvertebrate foodwebs in saline wetlands of the Laramie Basin (Wyoming)

This dissertation presents the results of a stable isotope survey (δ13C and δ15N) and complementary gut-content analysis of macroinvertebrates from wetlands in the Laramie Basin, Wyoming. Throughout, there is an emphasis on comparing different types of saline wetlands i.e., oligosaline versus mesosaline. The body of the results are organized into three main themes as discussed below.; The interpretation of stable isotope survey data was carefully scrutinized and compared to gut-content analysis. The main conclusion is that to avoid incorrect interpretation, stable isotope survey data should be complemented with independent observations such as gut-content analysis, especially for wetland macroinvertebrates. In particular, enrichment patterns of δ 15N should not always be interpreted as indicators of foodchain length or trophic level. A review of other likely interpretations of δ 15N enrichment is presented, as well as the idea that variations in the timing of nitrogen cycling can cause variations in δ15N enrichment.; The relative of importance of macrophytes versus algae for macroinvertebrates was compared for each wetland type. The main conclusion is that macroinvertebrate foodwebs in both oligosaline and mesosaline wetlands are supplied by algae. This finding stands in contrast to the traditional idea that wetland foodwebs are based mainly on macrophyte detritus. However, direct consumption of algal cells was not always the most important pathway. Extracellular products of algal photosynthesis present in biofilms appear to be quite important to consumers in these wetlands and are probably important in other wetland types as well.; The role of both top-down and bottom-up factors in explaining differences in macroinvertebrate assemblages was examined. One of the most important findings was that damselfly larvae consumed mainly chironomid larvae and zooplankton and did not consume amphipods. The balance of interactions between amphipods, chironomid larvae, and their predators has important implications in these wetlands and probably in similar wetland types.