UC Berkeley

Invasions have often been linked to reduced biodiversity, but the role of non-native species in the decline of native species is ambiguous. In a 2003 survey of four California vineyard regions, exotic spiders (Cheiracanthium spp.) were more dominant in vineyards with lower spider species diversity and reduced spider abundance. There was no evidence for the role of species interactions in the invasion of Cheiracanthium spiders, however, as native spiders from the same feeding guild were most abundant in regions with high Cheiracanthium levels. Comparison with a survey conducted 10 years earlier indicated that the recent invader C. mildei simply represented an addition to the spider community, with no apparent change in proportions of the congener C. inclusum. Invasion success is discussed with respect to agricultural habitat, as results suggest that disturbed conditions in many vineyards may favor Cheiracanthium spp. and native wandering spiders while decreasing overall spider diversity.