Lepidopteran richness patterns in North America

A long-standing objective of ecology has been to explain the basis for diversity patterns. Empirical evidence suggests that regional variation in richness of both animals and plants depends strongly on energy availability. The generality of the richness-energy hypothesis is limited by the paucity of analyses of invertebrates. which are much more diverse than the more thoroughly investigated vertebrate taxa. In this study. we consider two groups of North American Lepidoptera for which large-scale distribution data are available: the Papilionidae (swallowtail butterflies) and forest lepidopterans (moths based on the Canadian Forest Insect Survey). Energy, as measured by potential evapotranspiration (PET), statistically explains between 61 and 72% of the variability in the richness patterns of the Lepidoptera we have examined. It is the single best predictor of the richness of these groups, and the relationships have a very similar form to richness-PET relationships observed earlier in vertebrate taxa. After PET, Papilionidae richness is related to topographical heterogeneity. These patterns ore true both within and among biomes. These results suggest that the richness-energy hypothesis applies generally to bath vertebrates and insects in cold and temperate regions.