Parallel responses to whole-lake experiments: evidence for multiple attractors in zooplankton communities.

Kathryn L. Cottingham
National Center for Ecological Analysis and Synthesis
Santa Barbara, California

We assembled long-term records for plankton communities and environmental parameters in 8 reference and 10 experimentally manipulated lakes, then explored

Principal components analysis of all lakes revealed distinct community states characterized by the dominance of different functional groups of zooplankton. For example, there were states dominated by small cladocerans and copepods, predatory cyclopoid copepods, and _Daphnia_. Reference lakes generally remained within a single state through time, while manipulated lakes moved among states following experimental alteration of pH, nutrients, or food web structure. Similar manipulations (e.g., change in the abundance of planktivorous fish, lowered pH) applied to different lakes led to similar shifts in community structure. For example, the addition of planktivores to Tuesday, Peter, and East Long lakes (Gogebic County, Michigan, USA) shifted the zooplankton community from dominance by _Daphnia_ to dominance by smaller zooplankton. These parallel responses in different lakes, together with the stability of community composition in the reference lakes, suggest that there are multiple stable attractors in zooplankton communities.

1997 ESA Poster Project