COS 202-5 - Top-down effects of diving beetles (Dytiscidae) on temporary prairie pothole wetland macroinvertebrate communities interact with experimental warming and propagule source

Abstract: Environmental and climatic conditions are a key component in shaping ecosystems, and variability in these conditions yields uncertainty in the persistence of species. Dormant or resting stages are an adaptation which facilitates intergenerational persistence in temporally variable conditions, one example being the cysts of branchiopod crustaceans living in ephemeral wetlands. The localized accumulation of reproductive propagules within a wetland basin (an egg bank) over decades ensures that these organisms have a greater chance of hatching under favorable environmental conditions. Top-down control is another important factor in shaping communities and ecosystems, but it is unclear how warming and propagule bank composition interact with predation in temporary wetland communities. This study examined the influence of a common predator and experimental warming on seasonal wetland communities that developed from both locally and distantly sourced propagules. Three factors were manipulated in combination: egg bank source (collected in North Dakota only or a mixture collected in five states across the US Great Plains), passive heating, and additions of native, predatory dytiscid beetles caught in local prairie pothole wetlands. Invertebrates were sampled every three days over the six-week experiment. The results indicate that dytiscid beetles selectively prey upon different orders of branchiopod crustaceans depending upon the temperature of the water in which they reside. Warmer waters yielded greater numbers of clam shrimp, but beetles greatly depleted their numbers where present. On the other hand, beetles depleted populations of fairy shrimp only under cooler conditions. Based on these results, we hypothesize that dytiscids prey primarily upon fairy shrimp at lower temperatures but switch to clam shrimp at higher temperatures in these communities, which may be related to shifts in the behavior of both the fairy shrimp and the beetles. These shifts appeared to have consequences for algal abundance, suggesting a full trophic-cascade. Several other taxa also responded to these treatments, with patterns that suggest changes in food resources and competition. In conclusion, this study supports the idea that rising temperatures alone can alter species interactions, with consequent effects on community and ecosystem dynamics.