Lakes and rivers as islands: species-area relationships in the fish faunas of Ontario

Fish species richness in 82 lakes in Ontario, Canada was significantly correlated with surface area. In this region, latitude explained only a small amount of the variation in fish species richness. Thus, our study provides a clear demonstration of the relation between fish species richness and lake area without the confounding effects of latitude and physiography inherent in analyses from broader geographic regions. By comparison with the species-area relationship obtained, we show that acidification clearly depressed the number of fish species in 66 acid-stressed lakes in Ontario. Fish species richness was also significantly correlated with both drainage and surface areas of 21 Ontario rivers. Slopes of species-area regressions of lakes and rivers did not differ significantly, suggesting that species are added to these habitats at similar rates. However, our regression analyses show that rivers support more species of fish per unit surface area of water. Although these results are consistent with some predictions of island biogeography theory, we suggest that fish species richness is more likely to be a simple function of habitat diversity, rather than an equilibrial balance between immigration and extinction.