PREDATORS  IN  SALT  MARSH  FOOD  WEBS

Predators are one of the most important factors driving community structure and ecosystem function.  Not only can predators shape animal abundance and diversity, but predation pressure on herbivores can indirectly benefit plants.  Because predators are often lost to extinction at a much higher rate than organisms lower in the food chain, it is imperative to understand their role in ecological food webs.  While we have long understood that predators can positively affect plant production by feeding on herbivores (i.e., trophic cascades), more recently we have begun to understand that generalist predators rely on prey from different food webs (e.g. live plant, detrital, and algal), which can in turn increase their efficacy in herbivore suppression.  We previously used a stable isotope approach to determine whether prey availability and predator hunting style (active hunting versus passive web-building) impacted the degree to which the two most abundant predators on an intertidal salt marsh (both spiders) fed on prey from the live plant and detrital food webs (Wimp et al. 2013).  We are now examining the way in which spider body size affects reliance on the detrital food web over time.  Small spiders obtain more than 80% of their prey from the detrital food web, while larger spiders use plant-based and detrital prey equally.  Such body size differences in prey use may be related to protection from cannibalism, as detritus provides small spiders with a complex habitat structure that reduces encounters with larger spiders.  The role of the detrital food web in salt marsh food web dynamics has historically been under-studied and the plant and detrital food webs were treated as separate entities, yet these food webs are linked through generalist predators.