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Grizzly Bears, Salmon, Scavengers, and Ecosystem Based Fisheries Mangement

Pacific salmon are fantastic (and tasty) animals. They are born in freshwater, migrate to sea, and return to their natal stream where they spawn and die. They provide an enormouse pulse of marine derived nutrients to terrestrial systems. Predators, anBear and Salmond particularly bears, rely heavily on salmon. Humans also rely on salmon for livelihoods and food. My research evaluates salmon management goals and their impact on wildlife by quantifying the level of competition between salmon fisheries and wildlife users of salmon. Fishery certifiers such as the Marine Stewardship Council state that fisheries must have acceptable impacts on the ecosytem, but quantitative methods to determine whether these goals are being met are still lacking. I am working to develop these goals for Pacific salmon fisheries.

In addition to quantitative research, my current fieldwork near Haines, Alaska quantifies the importance of salmon carcasses to terrestrial wildlife. Using trail cameras, I record wildlife visitations to dead salmon, many of which were deposited on land by bears. (Original artwork by Yiwei Wang)

Human Livelihoods and the Conservation of Neotropical Wildlife

Subsistence hunting provides a crucial food source for rural populations in tropical forests but is often said to be unsustainable. However, previous methods treat sustainability as a binary 'yes' or 'no' question, which is particularly problematic because the answer to that question depends entirely on the spatial scale being considered. To remedy this, my research treats sustainability as an inherently spatial problem. Rather than label hunting as sustainable or not sustainable, I quantify the spatial area where hunting will cause local extirpation, and assess how this area depends on the adoption of firearms, human manupopulation growth, the creation of new settlements, hunter effort, and the speed at which animals recolonize hunted areas. Previous methods were also limited to assessing sustainability in a single settlement, but the models that I have developed predict wildlife population densities in space even when hunted by multiple settlements with overlapping hunting ranges and different human population sizes. My models also predict how human harvest rates change as wildlife are depleted, which has implications for the livelihoods of subsistence hunters. To make these methods accessible, I provide software-based tools, including a toolbox for ArcGIS, to assist in managing and mapping the spatial extent of hunting.

I have worked primarily with two large projects. The first is the People vs. Parks project in Manu National Park, Peru where I lived and worked with Matsigenka hunters to monitor hunting behavior and harvest. I recently joined Project Fauna in the Rupununni region of Guyana. Project fauna conducted ambitious wildlife sampling with the help of Macuxi and Wapishana Indians on a massive spatial scale. I use distance sampling and statistical models to assess how wildlife population densities relate to anthropogenic distrurbance, such as hunting, versus natural variation in habitat and fruit availability.

Predator Interference and the Community Ecology of Disease

There is a growing recognition that changes in host community ecology and trophic interactions can contribute to the emergence of infectious disease. Lyme disease, caused by the bacteria Borrelia burgdorferi, is the most prevalent vector-borne disease in North America and both the annual incidence and geographic range are still increasing. The emergence of Lyme disease, which is transmitted to humans primarily by the nymphal stage of Ixodes sp. ticks, was initially attributed to an increase in deer abundance because adult Ixodes ticks primarily use larger prey, such as white-tailed deer Odocoileus virginianus, as reproductive hosts.Canids However, once deer are moderately abundant further increases do not appear to influence tick densities. Further, because deer are not competent reservoirs for B. burgdorferi, they are not responsible for infecting ticks. Small mammals are the dominant reservoir host and their populations are positively correlated with the density of infected tick nymphs the following year. Small mammal populations are influenced by both food availability and predation. My research quantifies the importance of predators to the community ecology of Lyme disease. In particular I have used models to show that predation can strongly impact Lyme disease risk, and data across states to show that predation rates have likely decilne substantially over the last few decades as foxes have been suppressed by the expansion of coyote populations into the Northeast through the Upper Midwest.

I am also interested in the interactions of predator species and the causes and consequences of coexistence versus competitive exclusion. My research explores the possiblity that wolves suppress coyotes, which allows fox populations to increase. This has impications for our understanding of how top predators structure ecosysems. (Original artwork by Yiwei Wang)

Predator-Prey Dynamics in a Changing Climate

The reintroduction of wolves to Yellowstone National Park has sparked a long debate over whether (and how) wolves have facilitated a resurgence in tree recruitment. When a predator suppresses an herbivore to increase vegetation biomass or reproductive sucess, ecologists call this a "trophic cascade". Wolves can potentially cause trophics cascades in two ways, and there is still debate over which is more important. First wolves can simply kill enough elk to reduce their population density, which lowers herbivory rates (Ecologists call this a density-mediated trophic cascade). Second, wolves can simply scare elk into avoiding risky areas such as valley bottoms, which also lowers herbivory rates (Ecologists call this a trait-mediated trophic cascade). My research tries to predict elk behavioral strategiesand simulate elk and wolf populations under different scenarios. Most importantly, shorter and milder winters might greatly change the nature of wolf-elk interactions. In the current environment, wolves starve as they struggle to kill healthy elk in the summer months, but feast on weak and starving elk in the winter months. Starving elk may be forced to enter dangerous valley bottoms to find food in winter, but milder and shorter winters may allow elk to either avoid valley bottoms all together, or be so healthy that predation risk is low. I explore these relationships with dynamic state-variable models, game theory, and elk movement data obtained with GPS collars.