| Populations at the edge of their range are typically extinction-prone, and the probability of their persistence is challenged by habitat fragmentation coupled with rapid human population growth. At the interface of the Great Basin Desert and Sierra-Nevada Range including the Lake Tahoe Basin, black bears (Ursus americanus) have historically been ecologically restricted but they have recently experienced a rapid non-equilibrium response to increasing humans. To assess possible effects at contact zones, I tested predictions of resource-based models, first by contrasting biological features of individual bears between an urban-wildland interface (experimental area) and wildland areas (control area), and second by considering temporal changes in life-histories and ecology that span almost 15 years. Among the documented changes were: (i) declines of 90% and 70% in mean home range size for urban-interface males and females (respectively) relative to wildland bears (p < 0.05); (ii) body mass in which urban-interface bears averaged 30% more for both sexes relative to wildland animals (p < 0.05); (iii) alterations of denning chronology with urban-interface bears entering hibernacula later in the winter and emerging earlier than wildland conspecifics (p < 0.05); (iv) shifts in the pattern and amount of daily activity for bears in urban-interface areas relative to wildland conspecifics; and (v) bear densities which increased 3+fold in urban areas compared to baseline, historical densities. Additionally, since 1990 increases in the frequency of (i) urban-interface bears, (ii) collisions with vehicles, and (iii) citizen complaints were about 7000%, 1500%, and 1000% respectively. All mortalities (n = 59) since 1997 were due to anthropogenic causes. Finally, I examined the effectiveness of the six most common deterrents currently used by state and federal entities to alter the behavior of ‘nuisance’ black bears using 62 individuals. My results indicate that expanding but clumped urban foods facilitated a rapid redistribution of bears across this arid landscape. The careless provisioning of food, whether deliberate or unintended, may be operating at scales substantially larger than that described here. If so, the altered distribution of populations of other species may also be compromising ecological processes, an issue that awaits further attention from conservation biologists. |
