1. Natural Resource Ecology Lab; Department of Ecosystem Science and Sustainability; Colorado State University; Fort Collins CO 80523-1499 USA
2. School for Environment and Sustainability; University of Michigan; Ann Arbor MI 48103 USA
3. U.S. Geological Survey; Colorado Cooperative Fish and Wildlife Research Unit; Departments of Fish, Wildlife & Conservation Biology and Statistics; Colorado State University; Fort Collins CO 80523 USA