Elevational patterns of diversity are well documented, but the factors that shape them are poorly understood. Inconsistent findings across studies may result from the omission of fine-scale habitat information and from the pooling of species that interact in very different ways with their environment. Spiders are good subjects to evaluate these ideas, because they are small, microhabitat-sensitive organisms that can be classified into two ecologically different guilds: sedentary spiders that build webs and cursorial species that actively pursue their prey. We tested the hypothesis that the composition of spider communities across different slope aspects significantly differed at a given elevation. We also investigated whether differences in genus composition were shaped by different processes in each guild, by estimating the relative importance of geographic distance, habitat structure and temperature on the community composition of cursorial and web spiders.
Results/Conclusions
Elevation and slope aspect were significant predictors of spider density and species richness, and environmental factors played a key role in determining spider community structure. In some cases, the magnitude of variation in species abundance or richness across aspects at a same elevation was greater than that across different elevations. Differences in cursorial spider composition were strongly driven by temperature dissimilarity only, whereas differences across web spider assemblages significantly increased with dissimilarities in woody plant cover and temperature. This work suggests that fine-scale topographic variables cannot be ignored, and that a better understanding of the links between the biological traits of species and their environmental requirements should help uncover the mechanisms behind topographic patterns of diversity.