Gray wolves in a small park: Analyzing cumulative effects through simulation

Jean Fitts Cochrane, Conservation Biology Program, University of Minnesota, St. Paul, MN 55108, USA

I used stochastic, demographic population modeling to the assess the cumulative effects of human activities on gray wolves in and near a small park. Cumulative effects result from numerous, interacting conditions or impacts that may be individually insignificant, but affect population status when combined together over time or space. Because interactions between environmental and human variables are complex and poorly understood, cumulative effects analysis has rarely been applied to mammal populations. Computer simulation following a carefully developed experimental design provides one approach for evaluating cumulative impacts and supporting management decisions.

The computer model I developed depicts the environmental conditions and human actions that are most likely to affect a wolf population in a spatial arrangement resembling Voyageurs National Park, Minnesota. My analysis considered two spatial scales: regional trends encompassing such a small park and local disturbances within a small park.

My first simulation experiments addressed wolf population persistence under the combined influences prey supply, human-caused deaths, immigration, and disease. In my model, primary model parameters (wolf population demographic rates) responded to changing levels of these four impacts in a sequence of experimental simulations. The experiments explored which impact levels and combinations caused the greatest effects and which exceeded management thresholds, and whether any combinations produced non-linear impact-risk relationships that suggest alternative management objectives. In further experiments, I narrowed the experimental focus by simulating direct human disturbance effects on wolves inside the park. Disturbance was modeled in discrete increments such as movements or death of single wolves.