Spatial variation in species diversity and composition of forest Lepidoptera in eastern deciduous forests of North America

The primary emphasis of conservation biology has moved away from attempting to manage single species within a given habitat to the preservation of entire communities within ecoregions, requiring that greater attention be paid to how biodiversity and species composition vary across spatial scales. Using a nested sampling design, we examined spatial variation in the biodiversity of forest Lepidoptera across three hierarchical levels: 20 forest stands, five sites, and three ecoregions. We used blacklight traps to sample the moth communities of each forest stand every week in June and August of 2000. Lepidopteran community composition was most significantly influenced by ecoregional differences, whereas patterns of alpha and beta diversity across scales differed depending on how diversity was measured. Diversity partitioning models demonstrated that turnover in species richness occurred equally across all spatial scales because numerically rare species were continually encountered. In contrast, within-stand effects disproportionately influenced Simpson and Shannon diversity (relative to outcomes from randomization tests), suggesting that local factors determined species dominance. Because most Lepidoptera in forests appear to be rare (>50%), it will be impossible for conservation biologists to design management plans to account for every species. We suggest that a more meaningful strategy would be to identify species that attain a reasonable abundance within a community (5-10% of all the individuals in a sample) and that are unique to particular spatial levels. This strategy should produce two desirable outcomes: the conservation of species that render ecoregions distinct and the maintenance of functionally dominant species within forests.