In my dissertation research, I investigated factors that affect zooplankton community responses to acidification. Acidification has been a major environmental concern impacting aquatic communities throughout North America and Europe. However, the effects of acidification can be highly variable, such that some communities respond more sensitively than others.

In one aspect of my research, I explored the possibility that historical ecological conditions can affect community responses to current acidification. Using experiments conducted in three lakes with contrasting acidification histories, I demonstrated that community-level sensitivity to acidification can differ substantially among lakes. In a series of follow-up experiments, I discovered that these differences in community sensitivity can be attributed in part to evolutionary differences in the acid-sensitivity of populations. This study is the first to demonstrate that rapid evolutionary responses occurring at time scales less than a decade can modify community sensitivity to perturbation.

In another component of my Ph.D. research, I examined the role of compensatory dynamics in zooplankton responses to a whole-lake acidification. When compensatory dynamics occur (i.e., losses of sensitive species are matched by increases in functionally similar species), ecosystem functions may be maintained despite changes in species composition. I found evidence for compensatory dynamics in some functional groups of zooplankton; however, most zooplankton functional groups exhibited dramatic reductions in biomass due to simultaneous decreases in constituent populations. Interestingly, the occurrence of compensatory dynamics was not related to biodiversity as previous studies have suggested. Rather, my results highlighted the role of a few critical species which responded rapidly to offset declines in functionally similar species.