Facultative seed predators drive community-level indirect effects of mast seeding

Abstract

Mast seeding is a resource pulse that is thought to be a strategy in plants to satiate obligate seed predators. Behavioral responses of facultative consumers receive less attention in mast seeding studies despite evidence that they may be more important to community-level indirect effects. We designed an acorn addition experiment to test the hypothesis that mast seeding in oaks (Quercus spp.) generates indirect effects on the plant community by generating a behavioral response in white-tailed deer (Odocoileus virginianus)—the largest herbivore in the ecosystem and a facultative seed predator. Deer activity at masting trees increased substantially for months following acorn addition. Deer may require multiple dietary sources to satisfy energetic and nutritional demands and are consumers of oaks at multiple life stages. As such, acorn addition generated opposite density-dependent effects on seeds and seedlings. In acorn addition plots, we documented increased seed survival but decreased growth of oak seedlings relative to a common competitor. Importantly, acorn additions also resulted in different local plant assemblages than those at non-masting parent trees, which suggests that beta diversity may increase with localized variation in herbivory pressure. Overall, our results indicate that oaks may promote coexistence in the plant community by modulating spatiotemporal variation in herbivory pressure. These results highlight the important role of facultative consumers in linking resource pulses to the broader community.