Influence of Habitat and Region on Spider Communities Along Two Elevation Gradients in the Southwestern U.S.

Brantley, Sandra; Chapman, Caitlan; Cobb, Neil

There has been little research examining the changes in community composition of ground-dwelling arthropods along elevation gradients, and yet, understanding how species are distributed along elevation gradients is critical for understanding how such communities may respond to climate change. This report is one of few comparative studies of spider communities along elevation gradients in the Southwest U.S. We examined the abundance and community composition of ground-dwelling spiders along elevation gradients in northern Arizona (San Francisco Peaks) and New Mexico (Bandelier National Monument), respectively. Our questions were (1) how are spider species distributed across elevation gradients that span piñon-juniper, ponderosa pine, and mixed-conifer habitats, and are there fundamental changes in community composition, or degree of habitat specialization from low to high elevations; (2) how do these patterns compare between similar habitats in two regions of the Southwest; and (3) what is the importance of habitat structure versus geographic distance in terms of community structure and abundance. Key findings from this study were (1) species composition was distinct among habitats for both elevation gradients, despite no consistent differences in overall abundance and species richness; (2) species displayed a strong affinity for specific habitats, 59 percent of the 79 taxa were found in only one habitat type; (3) there was also a strong degree of regionalization, where 77 percent of the 79 species were only found in northern Arizona or northern New Mexico; and (4) habitat affinity was more important than geographic distance, in that spider communities were more similar among the same habitats in different states than communities in adjacent but different habitats in the same area.