Temporal shifts in spider foraging within a forest food web

Forest-dwelling spiders are thought to feed primarily according to prey availability. This is complicated, however, by the fact that prey populations show considerable spatio-temporal variation, and many of these prey items are of poor nutritional quality. The primary objective of this research was to identify spider predation shifts in response to fluctuations in seasonal availability of two common prey groups: Collembola and Brachycera (Diptera). Within an eastern deciduous forest ecosystem that is characterized by oak-maple stands, prey availability was monitored and, in parallel, the dominant spiders from the genus Schizocosa were collected for molecular gut-content analysis in order to delineate predation strength throughout the year. Prey availability and predation were correlated to identify reliance and food preference patterns of these predators. Despite significant variance in availability throughout the year, spiders fed independently of Collembola density. Consistent with previous studies, however, Collembola were an integral part of Schizocosa diets, with approximately 49% of spiders testing positive for Collembola DNA. In contrast, dipterans were rarely fed on, regardless of their availability. These results show a distinct preference for Collembola in spiders and may display an instance of selective foraging by a generalist predator.  Expanding DNA detection to other common prey groups will be important in future work to fully understand the dynamics of this food web on a temporal scale and will provide insight into the functional role of these animals in the forest ecosystem.