HELENA RHEAULT
RESEARCH PROJECTS
Abstract
Bison bison (plains bison) plays a critical role as an herbivore in Yellowstone National Park’s northern range. The current management strategies adopted by the Interagency Bison Management Plan (IBMP) lack a comprehensive understanding of the dynamics of the northern range ecosystem and the ecological role of bison. This study began with analyses of the northern bison herd population dynamics and annual vegetation consumption between bison and elk (Cervus canadensis), which led to a synthesis of the delicate ecological balance of the northern herd. Bison are now the dominant consumer of vegetation in the northern range and have likely been released from competition with the elk population post wolf reintroduction. Recruitment of woody vegetation is also likely still limited by cascading effects from elk and bison diet partitioning and new evidence of bison browse. In conclusion, the current strategies employed by the IBMP to reduce herd size and limit range expansion could result in counterproductive management strategies and the relationships outlined in this study need to be addressed by the IBMP to avoid creating negative long-term impacts on the northern range ecosystem.
Abstract
Wildlife populations are declining at alarming rates between 50-59% across Africa. Protected areas are not an exception to these declines. By identifying the species with the greatest declines, isolating the root causes, and assessing how this has shaped the structure of the overall community is ideal for wildlife managers to identify vacancies in management plans and evaluate appropriate interventions to prevent further declines. This study aimed to address these concerns in Lake Manyara National Park, located in northern Tanzania, which has population data ranging from 1959-2016. Thirteen herbivore species were included in this study: African elephant, hippopotamus, black rhinoceros, giraffe, Cape buffalo, common zebra, waterbuck, wildebeest, warthog, impala, reedbuck, bushbuck, and olive baboon. We used general additive models and other statistical methods to assess the species population trends, trends in community structure and biomass, and identify structural changes in the study period. These breakpoints were cross-referenced with documented local historical events. The main findings identified major population crashes of African elephant, Cape buffalo, and black rhinoceros, which resulted in a 42% loss of overall herbivore biomass. These events are mainly attributed to severe poaching in the 1980s, resulting in the local extinction of the black rhinoceros by 1992. This enacted a major regime shift in the park’s community structure that has begun to favour the spread of browsing species. The remaining species have overall faired relatively well, with many exhibiting fluctuations over the study period. This study supports prior research that anthropogenic disturbances are a major source of population declines and demonstrates how they can have impacts on an entire community system for decades beyond the initial affect.
This research project involved statistically evaluating certain reproductive trends in the Connecticut black bear population with data provided by the CT Dept. of Energy & Environmental Protection's ongoing black bear study. This project was completed as a component of a biostatistics course at Westfield.