PARENT SESSION
Oral Session #32: Animal Community Ecology. Presiding: M. Weiss.
Tuesday, August 7, 2001. 1:00 PM to 4:45 PM. Hall of Ideas P&Q.

Latitudinal gradients in the diversity of New World bat communities.

Willig, Michael¹, Stevens, Richard¹, ¹

ABSTRACT- The latitudinal gradient of species richness is well documented at coarse scales of resolution. The extent to which the pattern is recapitulated at the level of local communities is less clear. Consequently, we examined the way in which attributes of New World bat diversity vary with each other and with latitude at two scales of resolution, local communities and regional species pools. We calculated 14 indices of biodiversity [richness (3), evenness (4), dominance (3), and diversity (4)] based on species abundance distributions for 32 intensively sampled local sites. The species richness of each corresponding regional pool was estimated from published range maps. In general, the gradient of local species richness was less steep than the corresponding gradient of regional species richness; beta diversity in the tropics is greater than that for temperate communities. Aspects of diversity at the local scale did not vary with latitude in the same manner. The latitudinal gradient in species diversity of local communities was primarily a consequence of the corresponding gradient in species richness. Local richness increased and became more variable with decreasing latitude. In contrast, species evenness did not vary in a systematic fashion with latitude. Although the absolute number of rare species in communities increased faster with latitude than did common species, both abundance classes proportionately increased with latitude in equivalent ways throughout the New World. In general, latitudinal variation in diversity at the community level was a consequence of variation in indices that are insensitive to the abundance of species. The dramatic increase in species richness at broad scales of resolution toward the tropics (gamma diversity) was as much a consequence of increased richness at the local level (alpha diversity) as it was a consequence of the latitudinal increase in species turnover among communities (beta diversity). Future research should examine the correlates of latitude that effect differentiation among communities at low latitudes (i.e., those enjoying high productivities), whereas conservation strategies based on assessments of diversity at course levels of resolution should be implemented with caution, depending on the degree to which beta diversity inflates regional estimates of diversity.

KEY WORDS: latitudinal gradients, diversity, bat communities, macroecology