Ecology of a central Appalachian white-tailed deer herd at low density

White-tailed deer (Odocoileus virginianus) are the most abundant big game species in North America and serve as the dominant herbivore in the majority of the Appalachian region. Despite the abundance of research conducted on this species, relatively little is known of the ecology of white-tailed deer occurring at low densities. Our study population experienced a 75% decline in population density and a three-fold increase in habitat disturbance via timber harvests between 2002 and 2005. From May 2006 to April 2008 I examined the home-range, survival, and herbivory patterns of a central Appalachian white-tailed deer herd that has recently experienced both a substantial decline in population density and now occurs at extremely low densities (1--3/km 2). Home-range and core-area size did not differ among age classes in any season. Annual home-range size of yearlings (505 ha) was larger than for adults (313 ha), although core-area size did not differ. Within age classes there were no seasonal differences in home-range or core-area size. Home-range site-fidelity did not differ among age classes for any season or among seasons for any age class. Core-area site fidelity was higher in fall (74%) than in summer (45%) or winter (36%) when pooled across age classes but did not differ among age classes. Survival was lower during the fall (0.89) than during summer (0.99) or winter (0.94). Human-induced mortalities (n = 12) constituted 67% of all observed mortalities during the study; all mortalities were in the adult age class. Woody browse abundance differed among plot types, with clearcut interior (50.16 twigs/plot) plots having more browse than clearcut edge (31.95 twigs/plot) or mature forest (18.93 twigs/plot) plots. Browsing rates of woody plants was higher in clearcut edge plots (5.55%) than in clearcut interior (3.99%) or mature forest plots (3.32%). Observed home-range and core-area sizes were substantially larger than previously reported for the same population prior to declines in density. This supports previous work that suggests home-range size is inversely related to population density and positively correlated with habitat disturbance. Survival rates were similar to previously reported, suggesting that adult survival is robust to changes in population density. Previously reported browsing rates were approximately 5 times the levels reported herein, however such a decrease would be expected with reduced population density and an increase in browse abundance, both of which occurred on the study site

Understanding the dynamics of species distributions under climate change: linking empirical evidence, ecological theory, and statistical models

Climate change is threatening biota all over the world through dictating changes in species distributions. The ability to predict the effects of climate on species distributions requires an understanding of how climatic and disturbance factors relate to species distributions. I examined the relationship between climate, disturbance, and geographic distributions of vascular plants in the western United States. Within the mountain ranges of California, woody plants have largely shifted their distributions downhill during the 20th century. These shifts were strongly related to observed changes in climatic water balance, consistent with theoretical predictions. Downhill shifts were most prominent for species occurring at higher elevations where environmental conditions were marginal. Downhill shifts were observed at nested spatial scales where changes in climatic conditions were consistent, but at all scales were unrelated to species ecological traits. Niche models based entirely on climatic variables were highly accurate both within and across time periods. The inclusion of fire occurrence as an additional explanatory variable did not affect model likelihood or niche model transferability, due primarily to climatic influences on fire occurrence. Departure from historical return interval influenced total model likelihood when it was included as an additional explanatory variable for species adapted to high frequency return intervals, but did not improve model transferability for most species. Regeneration of tree species occurred within a narrower range of climatic conditions than adults. Species with greater niche breadth displayed greater differences between adult and regeneration niches. Both adults and juveniles displayed higher sensitivity to climatic variables representing mortality risk than to variables representing growth potential. Spatially explicit models of regeneration indicated overestimation of tree ranges based on niche models and the potential for future range contractions. These results were consistent across species

Psychosocial Factors Associated with Longevity in the United States: Age Differences between the Old and Oldest-Old in the Health and Retirement Study

Recent growth in the number of adults surviving to advanced ages raises questions about the quality of life associated with increased longevity. Psychosocial factors have received relatively little attention in research on quality of life among the oldest-old. This study uses nationally representative data on older US adults to examine how social relationships, feelings of loneliness, and satisfaction with life and the aging experience differ between the oldest-old, those who have survived to age 90 or older, and older adults in their 70s. We find that the oldest-old are able to maintain social relationships with family and friends and receive more social support than younger elderly adults. Yet, the oldest-old are more likely to feel lonely due to their greater rates of widowhood. Satisfaction with life was higher among the oldest-old, but the oldest-old had more negative perceptions of the aging experience. Psychosocial dimensions of longevity should be considered in research on quality of life among the oldest-old