Effect of disturbance and distance from a riparian corridor on spiders in a temperate rainforest

Abstract

In anthropogenically disturbed forested riparian ecosystems that contain vagile organisms, we expect dispersal to be a factor that determines patterns of diversity that differ from similar, but continuous, undisturbed habitats. We studied the effects of habitat alteration on community composition by characterizing the spider assemblage of a riparian corridor in an ancient forest and a regenerating coniferous forest in the Carmanah Valley, Vancouver Island, British Columbia. Spiders were collected over a 15 month period using Malaise traps set along transects perpendicular to Carmanah Creek. We recorded 76 genera and 113 species representing 23 families. In both the regenerating coniferous forest and the ancient forest, a large proportion of the species were of the family Linyphiidae. Species abundance was similar in the two habitats but diversity was greater in the regenerating coniferous forest. The ancient forest was dominated by the web-building guild. Spatial autocorrelation analysis revealed no overall pattern in the species assemblages relative to the riparian corridor. Bray–Curtis similarity measure and principal components analysis results indicate that spider assemblages in the two habitats were significantly different in composition. These results suggest that habitat changes affect assemblages of spiders by altering dispersal, and these responses are evident a decade after disturbance.