Spiders are key predators that use different strategies to capture prey. Species in the sedentary guilds forage by spinning a web, whereas those in the hunting guilds rely on active pursuit. We investigated whether the differences in exposure to the abiotic factors that vary with elevation and slope aspect influence habitat selection in these spider guilds. Since spiders are ectotherms, we hypothesized that guilds that use active strategies to hunt for prey should be more abundant on warmer slope aspects (south, west) especially at higher elevations, whereas sedentary guilds should not be as limited by lower temperatures, because their relatively passive lifestyle should reduce their dependence on optimal temperatures for prey capture. We investigated this proposition by sampling 240 sagebrush shrubs distributed over three sagebrush-dominated sites (low, intermediate and high elevation) in the Bear River Mountains, Utah. Each site contained 80 randomly chosen shrubs, equally distributed over four slope aspects (north, east, south, and west). We sampled shrubs over two periods, collecting and preserving over 7000 spiders for later identification.
Results/Conclusions Active hunter spiders were in significantly lower densities at the high elevation relative to the intermediate and low elevations. In addition, these active guilds were significantly more abundant on the warmer aspects relative to the colder aspects at the high elevation. In contrast, sedentary spiders showed (1) a peak in density at the intermediate elevation, (2) no difference in density between the low and high elevation and (3) almost identical densities on the south and north aspects at the high elevation. The lack of segregation in sedentary spiders as a function of slope aspect at the high elevation concurs with the idea that web-builders may be at an advantage over active hunters in harsher environments. Our findings suggest that sedentary and active hunter guilds show different responses to elevation and slope aspect and that our predictions were best followed at the highest elevation.
