Compensatory dynamics in zooplankton community responses to acidification:Measurement and mechanisms

Previous studies indicate substantial variation in ecological responses to perturbation. In some cases, ecosystems are resilient to perturbation due t o compensatory dynamics in which losses of sensitive species are offset by population increases of species that perform similar ecological functions. Here, we report a detailed evaluation of compensatory dynamics in zooplankt on community responses to the experimental acidification of Little Rock Lak e, Wisconsin, USA. We used a variance ratio to quantify compensatory dynami cs in functional groups of zooplankton containing Species that use similar resources and are vulnerable to the same predators. We also used first-orde r autoregressive models to explore mechanisms driving the dynamics of each functional group, Our results indicate that responses of functional groups to acidification can be highly variable. Herbivorous copepods and medium-si zed herbivorous cladocerans exhibited significant compensatory dynamics in response to acidification, whereas other functional groups, exhibited indep endent or synchronous dynamics. First-order autoregressive models indicated that groups exhibiting compensatory dynamics contained both acid-tolerant and acid-sensitive species that competed. In contrast, groups that containe d only acid-sensitive or acid-tolerant species exhibited more independent o r synchronous dynamics. Overall, our study highlights the combined roles of sensitivity to environmental perturbation and species interactions in dete rmining the extent of compensatory dynamics in zooplankton functional group responses to acidification.