Biogeography at a Regional Scale: Determinants of Ant Species Density in New England Bogs and Forests

We examined species density gradients of ants of New England in 22 ombrotrophic bogs and their surrounding forests. We tested the hypothesis that species density was correlated with large-scale geographic variables (latitude, longitude, elevation) and small-scale site variables (habitat area, vegetation composition, light availability). Species density was consistently higher in forests than in bogs. Ant species density measured in three other New World studies yielded similar results, with steeper diversity slopes in closed canopy vs. open habitats. In New England bogs and forests, latitude was the single most important predictor of species density, even though the latitudinal span of the entire study region was less than three degrees. Diversity patterns documented in our study of midlatitude ant communities are similar to those seen in studies spanning tropical and temperate habitats. Species density of forest ants was associated strongly with latitude, elevation, light availability, and vegetation composition. Species density of bog ants was less predictable and was correlated only with latitude and vegetation. Overall, our results suggest that species–energy relationships are important at regional spatial scales. Explanations for the latitudinal gradient in ant species density may not depend on unique differences between tropical and temperate communities, but could operate at all latitudes.