Linking species to ecosystems: predation-mediated nutrient flows

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A fundamental issue of theoretical and applied research in ecology is how species affect ecosystem functioning. Evidence has accumulated that large-bodied herbivores exert a strong influence on nutrient cycling within plant communities. Whether predators can modify nutrient dynamics either directly by reducing herbivore numbers or indirectly by altering herbivore behaviour remains unclear. My research addresses how herbivores alter their behaviours to avoid predators in a "landscape of fear", and then evaluates consequences for nutrient flow. Using data from field studies in the central east slopes of Alberta, I examine correlations between the distributions of wolves and elk in both time and space to test whether elk avoid wolves by concentrating in areas not used by wolves (i.e., refuges), by moving out of areas when wolves frequent them (e.g., shell game), or by avoiding habitats used by the wolves' preferred prey (e.g., segregation). Then, using direct observations of elk scanning for predators (i.e., vigilance) in open grasslands, I determine the effect of vigilance on intake. From a relationship between bite rate and plant biomass I predict the amount of "spare time" animals have available to scan for predators, and compare this to the observed time allocated to vigilance. Next, I determine whether bite rate declines as animals spend more time vigilant and how this changes with the number of conspecific foragers. Finally, I assess whether changes in elk distribution and feeding behavior alter nutrient flows by comparing net carbon and nitrogen return (in feces and urine minus forage removed) across a gradient of areas from low to high wolf predation risk. My work provides a mechanistic understanding of how the influence of predation can cascade down to lower trophic levels through nutrient flows that is not currently available for large mammal systems.