Responses of grouse to predation by Alaskan gyrfalcons and indirect effects on primary producers

Adam Eichenwald
Oswald Schmitz
Start Date: 
September, 2016

Predators are known to affect population abundance of their food sources through capture and consumption. However, the mere presence of carnivores can also result in behavioral and physiological changes in prey. Such changes are referred to as non-consumptive effects and can also affect the food source of said prey species, indirectly linking carnivores to plants. This concept, called a trophic cascade, is not well studied in avian systems. I propose an investigation to test for a trophic cascade between the gyrfalcon, its preferred food sources (the rock and willow ptarmigan), and the tundra plants consumed by ptarmigan. I predict that ptarmigan will increase herbivory, increase abundance, and decrease vegetation coverage surrounding their nests in areas of low gyrfalcon predation risk. I will also test for the presence of central place foraging effects, which predicts that a predator will spend less time foraging farther away from a home nest or den to avoid wasting energy. If gyrfalcon behavior follows the trends described in central place foraging, the risk of death for ptarmigan should decrease as distance from gyrfalcon nesting sites increases.

Such information is important for future arctic management plans. Ptarmigan browsing alters the structure of plants, allowing permafrost to remain frozen and keeping the arctic from becoming a source of atmospheric carbon. Understanding the interactions between ptarmigan and their primary predator will allow scientists to predict how such interactions may affect climate change, laying the foundation for well-informed, successful future Alaskan management plans