Long-Term Dynamics of Three Crayfish Species in Trout Lake, Wisconsin

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Abstract
Previous reports suggested that crayfish species composition in northern Wisconsin is changing unidirectionally because of the competitive hierarchy of sequential invaders. In Trout Lake, Vilas County, Wisconsin, we expected Orconectes virilis to decline in the presence of O. propinquus and for both to be displaced by O. rusticus. Our data show the abundance and species composition of Orconectes species in Trout Lake have been changing since 1931. A 1932 survey determined that O. virilis was the only Orconectes in Trout Lake. In 1973, we found that O. propinquus was abundant and O. virilis uncommon. Yet between 1973 and 1983 (probably between 1980 and 1983), O. virilis became much more widespread and abundant, while the population of O. propinquus declined. Between 1973 and 1979, O. rusticus invaded the lake, but has remained in low abundance. Both of our predictions are contradicted by our results. Orconectes propinquus has declined and O. virilis has increased, and while O. rusticus has invaded, it has not yet displaced the other species. We suggest that the outcome of interspecific interactions is variable and probably affected by other community structuring forces such as predation, parasitism, and disturbance, in addition to competition.