Fear-mediated cascades over four trophic levels affect seed predator function

Intraguild predation and nonconsumptive effects of predators are two enigmatic drivers of food web complexity with pervasive and profound impacts on ecosystem structure and function. Like all ecological processes, both are mediated by a suite of site-specific environmental variables that include refuge and food availability. Quantifying ecosystem-level effects of complex predator-prey interactions is a formidable challenge, but seed predator networks are a relatively manageable and largely unexplored system for examining how indirect interactions shape trophic cascades and plant population dynamics.  Focusing on two common taxa, mice (Peromyscus spp.) and ground beetles (Coleoptera:Carabidae), I use omnivorous seed predators as a model to simultaneously examine environmentally-mediated intraguild predation and nonconsumptive effects over four trophic levels; from a top predator to the plant population. Moonlight improves visibility for nocturnal avian predators, and small mammals are known to forage preferentially under vegetative cover in response to the indirect cue of predation risk. This predator-mediated habitat shift is likely in turn to alter the foraging behavior of seed-feeding carabids, which also preferentially use cover. This experiment measures the singular and interactive effects of multiple predators on the fate of common lambsquarters (Chenopodium album), a common invader of disturbed habitats across temperate regions. To determine whether or not carabid seed foraging activity is affected by the presence of a vertebrate predator, we manipulated the presence of cover, light, and vertebrate predators in replicated sites. These treatments enabled us to quantify the impacts of seed predator interactions on flux to the seedbank. Preliminary results provide evidence that cascading antipredator behavior by small mammals may interfere with seed feeding by carabids.