Latitudinal patterns of mammalian species richness in the New World: the effects of sampling method and faunal group

Although the latitudinal gradient of species richness for mammals in North America is well documented, few investigators have quantified the relationship in South America. We examined the pattern in North and South America, at two spatial scales (2.5 degrees and 5 degrees) for each of two sampling methods (quadrats and latitudinal bands). A scale effect was evident for quadrats but not for bands. Significant linear relationships between species richness and latitude were found for three faunal groups: all mammals, nonvolant species, and bats. Effects of area confound the latitudinal relationship. By statistically removing such effects, we found that the latitudinal gradient is not an artifact of the species-area relationship, and that the latitudinal gradients for North and South America were statistically indistinguishable. Our data suggest that both faunal subgroups, nonvolant species and bats, contributed substantially to the overall mammalian pattern. Further, multiple regression analyses showed that only latitude is a necessary variable to explain bat richness; for nonvolant species, in addition to latitude, area and longitude may be important.