Body size and dispersal ability of carabid beetles (Coleoptera: Carabidae) on an elevation gradient in a Neotropical cloud forest

Questions about relationships between species diversity and physical gradients have usually examined communities via richness estimators; however, morphological characters may also provide significant ecological and evolutionary insights. Analyses of altitudinal gradients are especially relevant in light of predictions of regional and global climate change. Tropical carabid beetles may be particularly useful to investigate altitudinal gradients due to their sensitivity to environmental changes, high species diversity, large range of body sizes, and variable wing state within and among species. Our study examined changes in body size and wing condition of carabid beetles along an elevation gradient in the high altitude cloud forests of Peru. Carabid beetles were collected on two parallel 2000 m gradients, one disturbed and one intact, along the eastern slopes of the Peruvian Andes. Carabid size, measured by apparent body length, and wing condition, e.g., fully winged or wingless, were recorded for beetles collected at five altitudinal zones over a multi-year period. Size was negatively correlated with elevation. Differences in wing state, which are presumably related to dispersal ability, varied by elevation, with a higher number of fully winged species at lower elevations. The number of fully winged species was also negatively correlated with elevation. The patchy distribution of low elevation tropical forests probably contributes to the high number of winged species; in patchy habitats, a high degree of dispersal ability may be favored when resources are difficult to find.