Tracking predation shifts in forest spiders over the cold season

Background/Question/Methods

Forest-dwelling spiders can profoundly impact the decomposer food web because of their prevalence in the leaf litter and their voracious appetite for detritivores. They are frequently food limited in terrestrial environments, however, causing them to forage simply according to availability of prey. This is complicated 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 seasonal spider predation patterns in response to fluctuations in prey availability, focusing on shifts in foraging dynamics during the autumn and winter, where there is the greatest paucity of information. Within an eastern deciduous forest ecosystem, prey availability was monitored and, in parallel, spiders were collected for molecular gut-content analysis in order to delineate predation strength throughout the season. Prey availability and predation were correlated to ultimately identify reliance and food preference patterns of these predators.

Results/Conclusions

Extensive monitoring throughout the winter revealed that spiders were the dominant predators in the forest floor food web. While intraguild competitors from Carabidae, Staphylinidae, and Formicidae were virtually absent by November, spider activity remained high from autumn through the winter. Over 500 spiders were collected for molecular gut-content analysis and showed that dietary diversity shifted during winter, as prey availability changed. Tomoceridae (Collembola), an important prey item for eastern forest spiders, remained active but decreased throughout the winter. In contrast, dipterans fluctuated in activity and increased significantly during February thus providing a critical pulse resource for these predators as alternative food items decreased in abundance. Molecular gut-content analysis revealed less selectivity in spider feeding when the breadth of prey available to spiders narrowed. Given that detritivores have a direct impact on forest decomposition rates through their grazing activities, arachnid predators have cascading effects on these ecosystem processes. Tracking seasonal feeding dynamics between spiders and their prey therefore provides valuable insights into their functional role in forest floor food webs.