Comparisons of the composition of foliage-dwelling spider assemblages in apple orchards and adjacent deciduous forest

Abstract

AbstractPrevious studies have shown that annual crops have different spider (Araneae) assemblages than adjacent relatively natural habitats, suggesting that spider recolonization of crops occurs via long-distance ballooning and that spider species in crops are mainly agrobionts. However, in perennial crops, e.g., apple (Malus domestica Borkhausen (Rosaceae)), which are subject to less physical disturbance than annual crops, overlap in spider species has been observed between tree foliage and adjacent habitats, suggesting that spiders colonize orchards from adjacent vegetation. The objective of this study was to compare the species composition of assemblages of foliage-dwelling spiders in apple orchards with that in adjacent deciduous forest and to determine whether spider assemblages in orchards are dominated by agrobiont species. Spiders were collected from four apple orchards and adjacent deciduous forest in southern Quebec from May until August 2004. The similarity of assemblages between the orchard and forest habitats was evaluated using nonmetric multidimensional scaling and multiresponse permutation procedures and spider species richness in the two habitat types was compared using rarefaction. Although spider species richness was higher in the forest than in the orchards, the composition of the spider assemblages in apple orchards was not significantly different from that in adjacent deciduous forest at three of the four sites. Therefore, adjacent deciduous forest, which is similar to orchards in vegetation structure and frequency of structural disturbance, is likely the main source of spiders found in apple orchards.