Patch shape alters spider community structure: links between microhabitat choice and sensitivity to increased edge habitat
Cobbold SM and Supp SR
Increased edge effects in fragmented habitats can affect the abundance of edge-dwelling organisms, but these impacts may depend on the biological attributes of species. We focused on how microhabitat choice, a species characteristic that reflects combinations of biological traits, may affect the ability of peripheral species to take advantage of increased edge habitat in the presence of edge effects. In this field study, we used artificial shrub modules designed to encourage web spiders to build webs on the periphery of modules. Modules were identical in volume, but differed in shape (cubic and elongated), so that elongated modules had more edge habitat and were subject to enhanced edge effects. We tested the hypothesis that Theridion, a genus that builds webs in more concealed locations and on a greater diversity of substrate configurations in the modules compared to Dictyna, would take better advantage of increased edge habitat.
Guild mobility and the perception of adjacent habitat structure in spiders of semi-arid shrubs
Cobbold SM and MacMahon JA
Modified vegetation structure strongly affects species distributions via changes in environmental and biotic conditions, but the response of species may depend on how they exploit resources. Mobility and movement patterns, in particular, may affect the way organisms perceive their landscape, especially in the context of habitat change. For instance, it is likely that sedentary species perceive habitat features at smaller spatial extents compared to mobile species. Spiders display two basic mobility levels based on foraging behavior: cursorial species are not restricted to specific sites whereas web-builders are sedentary. We collected spiders inhabiting sagebrush shrubs with different understory structures, to examine whether 1) habitat structure in the immediate vicinity of shrubs affected spider community structure within shrubs and 2) the two guilds exhibited different patterns.
Slope aspect and the distribution of spider species along an elevation gradient
Cobbold SM and MacMahon JA
Elevation gradients of species diversity are known in many organisms, but the links between local topography and animal distribution patterns are less understood. On the local scale, variations in slope aspect create a mosaic of microclimates that differ from the prevailing microclimate. These conditions in turn generate different vegetation characteristics. Given that spider species have distinctive thermal preferences and select for specific habitat structures, it follows that different slope aspects may yield different spider assemblages even if these slopes are at the same elevation. We are investigating spider assemblages on slopes of differing aspect in the Bear River Mountains, Utah, in an attempt to disentangle the effects of temperature regime and vegetation structure on the composition of spider communities.
