K. S. Summerville, T. D. Wilson, J. A. Veech and T. O. Crist
Abstract: Two of the major themes resulting from recent macroecological research are the central roles that body size and niche breadth may play as determinants of species geographic distribution. Using data on moth diversity in the eastern deciduous forest of North America, we tested the predictions that smaller-bodied and diet-restricted species would have lower levels of _-diversity within forest stands and greater _-diversity at higher sampling scales compared to larger or more generalist species. Body size for 492 species was estimated as mean forewing length, and diet breadth was assessed from the published literature. When observed diversity components differed from those derived from our null model a consistent pattern was observed: _-diversity was greater than expected, _-diversity among forest stands was less than expected, and _-diversity among sites and ecoregions was higher than expected. In contrast, diet-restricted moths contributed significantly less to stand-level _-diversity than generalist feeders. Furthermore, specialists contributed to a greater proportion of _-diversity across scales compared to generalist moths. Because absolute measures of _-diversity among stands were greater for generalists than restricted feeders, we suggest that regional _-diversity of forest moths may be influenced by several possible factors: intraspecific aggregation of diet-restricted species, local fluctuations in population size of eruptive generalists, and small geographic distributions of generalist moths than predicted by the geographic extent of putative host plants.