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Effects of Environmental Change on the Eco-Evolutionary Dynamics of Species in Natural Microcosm Communities
Natural communities are expected to undergo shifts in composition and species interactions as a result of environmental change, such as changes to regional temperature regimes and increased nutrient input into ecosystems. Predicting how communities will respond is complicated by three factors: non-additive effects of multiple stressors, differences in response among trophic levels, and trait evolution leading to adaptation. This study addressed all three of these factors using a natural microcosm community. The purple pitcher plant, Sarracenia purpurea, is a carnivorous plant that retains rainwater inside of its cup-shaped leaves. Within this water, an inquiline community of microbes and invertebrate larvae forms. I used a subset of this community consisting of a single protist species, Colpidium sp., and a community of bacteria to explore how the interaction between temperature and increased nutrient input affects different trophic levels ecologically and evolutionarily. I factorially manipulated temperature and nutrient input and maintained these conditions for 28 days (~150 protozoan generations). I then performed reciprocal transplants to each treatment, resulting in four common garden environments to test how evolutionary effects may depend upon ecological context. I found that historic nutrient input levels affected two protist traits - cell size and peak density - but the magnitude of these effects depended on the contemporary environment. The combined effects of historical temperature and nutrients did not differ significantly from the expected additive effect. Protist and bacterial abundances differed in their response to treatments, with protist abundance affected by both historical and contemporary environments while bacterial abundance was only affected by contemporary environment. Finally, bacterial community composition was affected by treatments both directly and indirectly, through their effects on protist traits and abundance. The results of this study show that the ways in which communities respond to environmental change can differ in light of evolutionary responses, the trophic levels being considered, and additivity of multiple stressors. The future success of management and conservation of natural systems rests upon the best possible understanding of not only the ecological implications but also, and perhaps even more importantly, the evolutionary consequences of a changing abiotic environment.