Patterns and prediction of α and β diversity of aquatic plants in Adirondack (New York) lakes

Patterns in α diversity (species richness) of submersed and floating-leafed aquatic plants were investigated for 45 lakes in the Adirondack region of northern New York State. Multiple linear regressions were used to build predictive models of species richness; the independent variables included lake surface area, approximate littoral zone area, pH, and measures of isolation and connectedness. The regression models that explained the most variance in species richness incorporated pH, a connectedness predictor, and either lake surface area or littoral zone area (r 2 = 0.74). The two area measures accounted for a majority of the variance in species richness (about 57%), but neither was a superior predictor to the other. When acidic lakes were systematically removed from the multiple regression model, r 2 tended to increase. The coefficient of determination was maximized (at r 2 = 0.822) when we limited the data set to lakes with pH > 5.6. As there was no significant correlation between pH and any of the isolation or connectedness measures we used (maximum r = 0.18), acidic lakes are not more isolated than circumneutral lakes. Point β diversity (the heterogeneity of species composition among sites) was measured for each pair of lakes. It was not strongly correlated to either the difference in surface area or the difference in pH between pairs of lakes. Standardized nestedness was calculated following Wright and Reeves (1992, Oecologia 92 : 416 – 428). Adirondack lakes are moderately nested. An implication of this is that species that are found in less diverse lakes have a 44% probability of being found in more diverse lakes. Key words: Adirondacks, aquatic plant, β diversity, biogeography, lake, nestedness, pH, species richness.