Habitat and season in structuring ground-dwelling spider (Araneae) communities in a shortgrass steppe ecosystem

We assessed habitat differences in ground-dwelling spider communities that stem from fine-scale differences in plant cover types and height in a short grass 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, Ju ne, July, and August 1995 and 1996. Spiders in the Lycosidae (56%) and Gnap hosidae (29%) were the numerically dominant spiders collected. The Lycosida e was represented by three species and significantly more abundant in grass habitats in 1995 only. The Gnaphosidae was the most speciose family collec ted (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 anal! sis revealed signi ficant species-specific differences ill the spider communities between the two habitats. Of the 10 most abundant species, Schizocosa mccooki (Montgome ry). S. mimula (Gertsch), Gnaphosa clara (Keyserling),and G. brumalis (Thor ell), were more abundant in grass sites. The most abundant spiders in the m ixed-grass/shrub habitat were Schizocosa spp. (immatures), Gnaphosa spp. (i mmatures), G. sericata (Koch), Haplodrassus signifer (Koch). Habronattus al tanus (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 comp osition were similar both years of the stud,. Our results underscore the im portance of habitat selection at fine-scales and patterns of seasonal activ ity that translate to population and community patterns at larger spatial a nd temporal scales.