Translating individual movements into population patterns: American marten in fragmented forested landscapes.

摘要

Some of the most pressing conservation concerns are for species that require large, intact landscapes. Yet, we have little information on what intact landscapes functionally mean for such species. Over 4 winters, I followed and mapped the movements of American marten in the western Yellowstone region of Idaho and Wyoming, USA. Movements and behaviors of individual marten were documented by following 145 snowtracks of animals (308 km) as they moved through landscapes highly impacted by clear-cut logging practices. In Chapter One, I break these paths into their component parts, steps and turning angles, to examine fine-scale movement patterns. Marten exhibit subtle movement responses, including changes in average step length, turning angle acuteness, autocorrelations in these parameters, and correlations betweens these parameters, in response to environmental or behavioral stimuli such as clear-cut forest patches or recent foraging activities. While marten paths exhibit some characteristics that may allow for their movements to be modeled as correlated random walks, the diversity of fine-scale movement responses create movement patterns that are poorly approximated by the more tenable of correlated random walk representations. In Chapter Two, I develop an approach to analyze habitat use along movement paths, using spatially-explicit bootstrapping methods within a GIS framework. I bootstrap paths with characteristics similar to the observed paths to generate expected habitat use patterns, and analyze the results using a variety of techniques appropriate for differing sample sizes. Large sample sizes allow habitat preference model evaluations that provide the most powerful and informative approach. The avoidance of clear-cut patches is the best predictor of how martens move across landscape. A preference for moving through structurally complex forests may also influence movement. In Chapter Three, I examine how responses of marten partially determine their ability to contend with increasing amounts of clear-cut habitat within the landscape. These responses include changes in the tortuosity of paths, distances moved between foraging sites, and types of habitats used foraging. Additionally, marten response to clear-cuts, habitat edges and potential corridors both enhances and limits their ability to successfully navigate fragmented landscapes. Forest management implications of the research are discussed.