The Spatial Dispersion of Spiders in a Cotton Ecosystem.

Abstract

In a cotton field in south-eastern Queensland, the spider species Cheiracanthium mordax L. Koch (diversum L. Koch), Archaearanea veruculata (Urquhart) and Lycosa sp. were equally distributed in the outer, middle and inner portions. However, A. veruculata was more abundant in the western side of the field late in the season, apparently in response to a more favourable habitat. In sampling, the variance was greater than the mean and overdispersion was apparent. C. mordax and A. veruculata were most abundant in the top one-third of plants, and Oxyopes mundulus L. Koch was evenly distributed over plants. The consistency with which these spiders were recorded in levels of vertical strata was enhanced by the formation of the crop canopy, and the eventual vertical distribution of C. mordax was apparently influenced by rainfall. Among crop spacings, most spiders of 4 species preferred the highest density (12 plants/m). The ecological consequences of the distribution characteristics are discussed in relation to current sequential decision plans for the management of cotton pests and beneficial species in the region.