Disturbance-driven change in hippopotamus behavior influences ecosystem structure and biodiversity
Much of my work on hippos (Hippopotamus amphibius) occurs in the Ruaha-Rungwa watershed, along the Great Ruaha River in Tanzania. Like many rivers in sub-Saharan Africa, the Great Ruaha River has been severely impacted by anthropogenic water extraction, reducing dry season river flow to zero. During the day, hippos spend the majority of their time resting submerged in river pools and emerge at night to forage in terrestrial environments. Because of their daily movements between terrestrial and aquatic systems, hippos vector significant amounts of terrestrial vegetation into aquatic systems through their dung inputs. Furthermore, because hippos are semi-aquatic, the availability of water is essential for their survival. Thus, human-induced changes in river hydrology is likely to influence hippo behavior and spatial ecology. The goal of this project is to understand how altered river flow may influence hippo behavior and the cascading effect that potential changes in hippo behavior may have on ecosystem structure and function. This projects seeks to understand: 1) the relationship between river flow and hippo spatial ecology, 2) how hippo movements influence the distribution of hippo-vectored nutrients, 3) how hippo dung inputs alter water chemistry and how these nutrients scale-up to influence watershed-scale aquatic biodiversity levels, and 4) how river flow and hippo movements influence the spatiotemporal spread of disease outbreaks. The extreme seasonal drying of the Great Ruaha River provides a unique context to quantify how human-induced changes in wildlife behavior may influence higher levels of ecological organization.
Altered river flow influences hippo movement and home range use. During the dry season, large subadult males exhibit upstream movements in search of available water. In addition, the drying river results in an increase in the size of hippo aggregations. The combined effect of hippo movements and aggregation size influence the distribution and accumulation of hippo dung inputs. Increased dung inputs significantly alters water chemistry and watershed-level biodiversity. Furthermore, altered river hydrology indirectly facilitates the spread of Bacillus anthracis – the causative agent of anthrax – by influencing both hippo movements and social behavior.
Tri-trophic relationships in engineered environments (Project TREE)
African savannas are intensively managed in the face of global climate change impacts including woody thickening/bush encroachment. In an effort to combat the advancement of bush encroachment and maintain savanna community dynamics, many land managers across southern Africa implement a number of habitat management regimes, including large-scale tree removals. These diverse management practices can alter vegetation dynamics and structure, which in turn, influences both bottom-up and top-down processes. Both top-down and bottom-up processes can have quantitative (e.g., change in abundance without compositional changes) or qualitative effects on herbivores (e.g. changes in community composition), which have important implications for species diversity and ecosystem function. Understanding these processes, and the resultant herbivore communities, allow predictions to be made about the response of herbivore assemblages to changing environments. Ultimately, the conservation of savanna ecosystems depends largely on how they respond to disturbances and the cascading effects that these responses may have on higher trophic levels.
Large-scale vegetation management can influence both bottom-up and top-down processes. These processes can influence herbivore distributions, herbivore habitat selection, and ultimately, predator-prey dynamics. Understanding these processes can have substantial implications for managing biodiversity and other important ecosystem processes and services provided by savannas in a rapidly changing climate.
wildlife conservation and management on Private and communal rangelands
Oribi antelope (Ourebia ourebi) are highly selective pure grazers. They are listed as endangered in South Africa. In this region, the majority of oribi occur in rangelands outside of protected areas and, therefore, interact with various management regimes and anthropogenic factors. Thus, my research goal is to aid wildlife conservation and management in human-dominated landscapes. Specifically, I am interested in how the presence of livestock may influence the structural heterogeneity of rangelands under different grazing pressures and how this altered heterogeneity may influence 1) the quality and quantity of food resources and how this may influence the coexistence of wildlife and livestock through competition and facilitation, and 2) the mechanisms driving oribi distribution and habitat selection over multiple spatial scales (i.e., feeding patches to habitats). In addition, student-led research has focused on oribi population assessments in both protected areas as well as private rangelands to identify important drivers of oribi population dynamics across South Africa, as well as assess the efficacy of oribi translocations as a management tool. The above research can be directly applied to supplement current habitat and population viability analyses for oribi antelope in South Africa.
Using a giving up density approach (GUD) to identify the mechanisms driving oribi landscapes of fear and habitat use, combined with detailed foraging studies, can provide wildlife managers with vital information to asses how livestock foraging under different stocking rates may influence oribi distributions, predation risk, and population dynamics.