Elevational variation of spider and insect communities in the Swedish mountains

Mountain topography gives rise to often dramatic climate-driven elevation gradients in primary productivity, which can generate substantial biodiversity variation. Therefore, mountain areas may be particularly useful for evaluating the ecological consequences of climate change. Arthropods are the most diverse animal phylum, which play important roles in most ecosystems. However, despite their ecological importance, we have limited information on how arthropods vary along elevation gradients. We investigated how taxonomic richness, taxonomic composition, and spatial structuring of spider and insect communities varied along elevation gradients and among three geographic locations in a mountain region of northern Sweden. The locations provided a latitude gradient spanning approximately 3 degrees (from 62 degrees N to 65 degrees N), but were otherwise selected to contain similar environmental characteristics. Taxonomic richness of both spiders and insects declined monotonically with increasing elevation, and there were limited differences between the geographic locations in such declines. Taxonomic composition varied with elevation for both taxonomic groups, but also differed among the three sites. Linyphiid spiders were more widely distributed along the elevation gradients than other spider taxa, whereas a broad taxonomic range of insects occurred over almost all elevations. We observed nested as well as modular spatial distributions of both spider and insect communities along the elevation gradients. While the modular patterns suggest that species turnover has generated distinct communities at different elevations, some generalist species were still widespread throughout large parts of the gradients. Our results point to smaller differences among geographic locations than among taxonomic groups in how taxonomic richness and community structuring varied with elevation. We interpret these results as support for taxonomically specific adaptations to environmental conditions being important for structuring arthropod communities. We also suggest that climate-driven changes to arthropod communities in mountain environments may be regulated by two not mutually exclusive processes, one in which generalist species may become more dominant and shift their ranges upward and one in which high-elevation specialists may go extinct because of increasingly fragmented habitats.