Biogeographic Influences on Fish Species Composition of Northern Wisconsin Lakes with Applications for Lake Acidification Studies

Abstract

Species–area relations, used to predict the number of fish populations lost in acidified lakes, may overestimate the number of extinctions if regression equations developed from unacidified (high-alkalinity) lakes are used to predict the number of species previously present in acidified (low-alkalinity) lakes. In 100 northern Wisconsin lakes, the species–area regression for alkaline lakes (>10 mg/L as CaCO3) had a higher intercept and greater slope than the regression for low-alkalinity, but unacidified lakes. Thus, low-alkalinity lakes had fewer species than alkaline lakes, and added species at a slower rate as lake size increased. Biogeographic factors (lake size, alkalinity, isolation from other water bodies) strongly influenced fish community composition. Small lake size appeared to exclude species requiring wave-washed, rocky substrates and species preferring cool, well-oxygenated water; such habitat is limited in small lakes. Low alkalinity and associated chemical conditions (e.g. low pH) limited the occurrence of many cyprinids and some percids (genus Etheostoma). Lake isolation (no inlet and outlet streams) appeared to have a limited effect on species composition. An exception was the reduced occurrence, in lakes without tributary streams, of species that spawn in flowing water. Fish distributions among Wisconsin lakes provide a test of habitat requirements proposed for other geographic regions.