Zooplankton community responses to acidification: the role of rapid evolution and compensatory dynamics
Understanding the processes affecting community responses to perturbation is a fundamental challenge in ecology. In my dissertation, I have focused on the processes affecting freshwater zooplankton community responses to acidification. In Chapter 1, I explore the possibility that acidification history can cause evolutionary changes in population acid-sensitivity which translate to differences in community level responses to acidfication. Using a combination of experimental approaches, I demonstrate that a) community sensitivity to acidification can differ substantially among systems with different acidification histories and b) these differences in community sensitivity can be attributed to evolutionary changes in acid sensitivity of populations. While there are numerous examples of evolutionary changes in natural populations, little attention has been paid to the community level consequences of such population differences. This study is the first to demonstrate that rapid evolutionary responses occurirng at time scales less than a decade can modify community sensitivity to perturbation. In Chapter 2, I explore the responses of crustacean zooplankton to the experimental acidfication of Little Rock Lake, Wisconsin. Specifically, I examine the dynamics of four functional groups of crustacean zooplankton which were chosen to represent species that use similar prey resources and are vulnerable to the same predators. I demonstrate that the responses of zooplankton functional groups to acidification can be highly variable. There was evidence for dramatic reductions in biomass for some functional groups due to synchronous decreases in consitituent species. Other groups were more resilient to acidification due to compensatory dynamics wherein the loss of sensitive species was offset by increases in functionally similar species. Overall, my results highlight the role of species-specific acid tolerance and competitive interactions in determining functional group responses to acidification.