Topographic Determinants of Faunal Nestedness in Great Basin Butterfly Assemblages: Applications to Conservation Planning

Abstract

Abstract: We examined factors possibly responsible for a nested distributional pattern of resident butterflies in the Toquima Range, a mountain range in the Great Basin of western North America. In related analyses, Poisson‐based modeling indicated that species richness is better explained as a function of elevation and local topographic heterogeneity than by area per se. Therefore, we explored whether area, elevation, and topographic heterogeneity affected relative degree of nestedness. Elevation and topographic heterogeneity not only explained a significant percentage of the total deviance in species richness but also may be responsible for generating nested species distributions. The species‐presence matrix ordered by the elevation‐heterogeneity model was significantly more nested than the matrix ordered by area. The matrix ordered by the elevation‐heterogeneity model also was significantly more nested than matrices ordered by three other environmental variables that did not explain significant variance in species richness, indicating that the model is unlikely to be an artifact. The influence of area on distribution patterns may be relatively slight because it was not significantly correlated with species richness or topographic heterogeneity in this system. Elevation covaried with both species richness and area, but the former correlation was positive and the latter was negative. Our results suggest that faunal richness and compositional patterns are related to independent variables that can be measured extensively—through satellite or airborne telemetry—thus reducing dependence on labor‐intensive measurements of habitat. Because nestedness analyses may help reveal causes, or at least correlates, of species composition, we believe they are a promising tool for conservation planning.