Abstract:
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 (from 62 N to 65 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.
