Demographic, behavioral and physiological responses of wildlife to reintroduction.

摘要

The growing field of reintroduction biology focuses on the process of restoring extirpated species to previously occupied habitat. Beyond academic interest, these fields have facilitated the reintroduction of charismatic and ecologically important mammals, which have been inspiring to wildlife conservation and critical to restoration of ecosystem functions. However, fewer than 11% of all reintroduction attempts have successfully reestablishing extirpated wildlife populations. To improve the outlook for conserving species and to strengthen natural resource management, I evaluated factors influencing reintroduction success.;Success can be defined in several ways. Often, it is defined demographically, wherein reintroduced populations need to reach a critical size before they are considered successfully recovered. The black-footed ferret, one of the rarest mammals in North America, is a leading example of a species having difficulty in recovering demographically after reintroduction. Following extirpation in the wild, over 3,000 ferrets have been released at 19 reintroduction sites in the western United States as well as in Canada to Mexico. However, ferrets at only four of these sites have succeeded in maintaining self-sustaining populations. I compiled and analyzed data collected over the 21-year history of the ferret reintroduction program to test hypotheses about environmental and management factors that might influence demographic success. I found that ferrets are likely to establish self-sustaining populations only at reintroduction sites that contain large populations of their primary prey. Successful sites were only located on prairie dog complexes >4300 ha in size regardless of prairie dog density. This finding is important, given that prairie dog populations are declining across the western United States, and that all reintroduction efforts over the past 10 years have been at sites 4300 ha in size. Thus, management efforts should focus on preservation of the declining prey base prior to future reintroductions of this critically endangered carnivore.;For large and potentially dangerous species like African elephants, the success of wildlife reintroduction can be defined in terms of how well the animals adjust behaviorally to their translocation. Once nearly extirpated from South Africa, reintroduction of African elephants has become increasingly common, yet behavioral problems have occurred post-release that have been linked to physiological condition and elevated stress hormone concentrations. However, there is uncertainty about the generality of a stress response in reintroduced elephant populations and the amount of time needed to physiologically adjust (i.e. decline of stress hormones from elevated to basal levels). I assessed stress hormone concentrations in elephants that were reintroduced into five reserves in South Africa over a six year period to evaluate the relationship of temporal, climatic, and social factors to elephant physiological state. I found that variation in stress hormones across the five reserves was best explained by the number of years that elapsed since initial release. Fecal glucocorticoid stress hormones were 10% lower 10 yrs after release, and 40% lower 24 yrs after release in comparison to 1 yr after release. Thus, regardless of reintroduction site conditions, elephants will require an extended period of time to physiologically adjust to their new surroundings and managers should prepare for prolonged pathological consequences of chronic stress responses.;Chronic stress in elephants following reintroduction can have multiple behavioral consequences. I compared space use patterns of reintroduced elephant populations in differing physiological states and found that elephants in a chronic physiological state exhibited refuge behavior. Refuge behavior was associated with elephants exhibiting smaller home ranges than expected and only utilizing a restricted portion of the reserve away from human disturbance. Therefore, the provision of refugia away from human disturbance following release is likely critical to limiting dangerous human-elephant interactions.;At a finer scale, I found that elevated stress hormone concentrations influence elephant movement behavior. Understanding elephant movement is critical to reserve design, as well as predicting elephant responses to management conditions. I found that the physiological state of elephants can affect fine-scale movement based on memory and environmental conditions. Elephants in iSimangaliso Wetland Park in elevated physiological states were less likely to utilize areas away from refugia and cover provided by commercial forest plantations compared to when they were in basal physiological states. These findings reveal connections between typically hidden physiological states and observed elephant behaviors, and provide useful information to managers on how to predict and potentially mitigate future human-elephant conflicts.;Collectively, results from my dissertation advance our understanding of reintroduction biology by illuminating factors that influence reintroduction success demographically, while also advancing our understanding of behavioral and physiological responses of wildlife to reintroduction. An understanding of these factors is needed if current and future reintroduction attempts are to succeed in restoring extirpated species and their ecosystems.