Habitat and Season in Structuring Ground-Dwelling Spider (Araneae) Communities in a Shortgrass Steppe Ecosystem

Abstract

We assessed habitat differences in ground-dwelling spider communities that stem from fine-scale differences in plant cover types and height in a shortgrass steppe ecosystem. The number of spiders captured in pitfall traps was used to determine habitat and temporal dynamics in the spider communities. Two habitat types were sampled, grass and mixed-grass/shrub during May, June, July, and August 1995 and 1996. Spiders in the Lycosidae (56%) and Gnaphosidae (29%) were the numerically dominant spiders collected. The Lycosidae was represented by three species and significantly more abundant in grass habitats in 1995 only. The Gnaphosidae was the most speciose family collected (15 spp). The most abundant species of Gnaphosidae exhibited consistent habitat and seasonal patterns of species turnover and abundance during the 2-yr study. Results from detrended correspondence analysis revealed significant species-specific differences in the spider communities between the two habitats. Of the 10 most abundant species, Schizocosa mccooki (Montgomery), S. mimula (Gertsch), Gnaphosa clara (Keyserling), and G. brumalis (Thorell), were more abundant in grass sites. The most abundant spiders in the mixed-grass/shrub habitat were Schizocosa spp. (immatures), Gnaphosa spp. (immatures), G. sericata (Koch), Haplodrassus signifer (Koch), Habronattus altanus (Chamberlin), and Xysticus nigromaculatus (Keyserling). Overall, the spider communities differed between grass and mixed-grass/shrub habitats in their response to seasonal change, and these differences in community composition were similar both years of the study. Our results underscore the importance of habitat selection at fine-scales and patterns of seasonal activity that translate to population and community patterns at larger spatial and temporal scales.