Response of fish communities in five north temperate lakes to exotic species and climate

Exotic species invasions and climatic variation that occurred in north central Wisconsin provided the opportunity to contrast influences of climate and invasive species in shaping fish community dynamics in five Wisconsin lakes from 1981 to 2001. Year (passage of time) was positively correlated (r > 0.9) with invasive species. Year, invasive species, and climatic variables were the principal determinants of fish community dynamics according to redundancy analysis (RDA). The same invasive species negatively affected the same general group of species in different lakes; benthic invertivores declined in lakes invaded by crayfish, Orconectes spp., and pelagic zooplanktivores declined in lakes invaded by rainbow smelt, Osmerus mordax. Micropterus dolomieu, Pimephales notatus, and Notropis volucellus increased in abundance in lakes invaded by crayfish. When year was included in RDAs as a covariable (partial RDA), fish community changes in three lakes did not differ significantly from ordinations of Monte Carlo simulated data; for two lakes, growing season length and lake productivity were significant explanatory variables under the reduced model. The resulting shifts in the fish community might represent declines in those species that used resources similar to the invading crayfish and smelt or were eaten by the invading smelt. Subsequent community compensation might have occurred, with other species increasing in response to the declines in species affected directly by the invasive species.