Structure of communities of ground-living spiders along altitudinal gradients

Differences in the altitudinal composition of ground-living spider communities were studied by pitfall trapping in western Norway. These data plus compilations of information from the literature were used to investigate features in the size composition, temporal appearance and spatial distribution of species. Spiders at the highest altitude had the widest distribution both in terms of geographical and altitudinal range. At the lowest altitude species were more often stenochronous than at higher altitudes. The size composition, reflecting food choice of the spiders, tended to be bimodal with increasing altitude. It is argued that small spiders are segregated mainly along the habitat dimension (searchers), while the larger ones are segregated with respect to diel activity patterns and food choice (pursuers). We suggest that mountain spider faunas in temperate regions at high latitudes mainly consist of widely distributed and easily dispersed species.