Research Interests
Our research focuses on how large mammalian herbivores (a) locate, assess, and obtain food resources, (b) evaluate and respond to predation risk, and (c) in turn, how their foraging decisions translate to population- and community-level patterns in space and time. The goal is to gain predictive insight into the population responses of large mammalian herbivores that helps inform their management and conservation.
We use aspects of behavioral ecology, physiology, evolution, and chemical ecology to address ecological questions at the individual, population, and community levels. This work is largely field-based, although we conduct a wide range of laboratory analyses.
Much of our work is based in African savannas, which are highly diverse in terms of both flora and fauna.
Within savanna systems, the distribution of mammalian herbivores is influenced by food availability (trees and/or grass), food quality, and predation risk (i.e. the risk of being eaten). However, the distribution of mammalian predators is not only influenced by food availability, but also by hunting success. Ultimately, the combination of food availability/quality (whether it be the distribution of trees/grass or mammal prey species), fear, and hunting success are all influenced by savanna habitat structure, which often consists of a mosaic of patches with highly variable ratios of trees to grasses.
Project TREE (Tri-trophic Relationships in Engineered Environments)
Under current climate change scenarios, bush encroachment (i.e. woody thickening) is predicted for many parts of southern Africa. As climate change progresses, African savannas will likely see an increase in the amount of woody vegetation and a significant reduction in the amount of grasses, resulting in more closed-canopy ecosystems. In an effort to combat the advancement of bush encroachment and maintain savanna community dynamics, many land managers across South Africa have actively implemented a number of habitat management regimes, including large-scale tree removals.
These management regimes alter not only the vegetation species composition and structure, but likely also influence the behavior, distribution, and population sizes of many prey species that track the availability of food resources. This ultimately could have a cascading effect on the apex predators that rely on these prey species as a food resource. Understanding the consequences of continued woody encroachment, as well as the outcomes of the management practices being implemented, is of critical importance to savanna ecosystem functioning.
Project TREE is based on first assessing how long-term tree removal and mowing influence availability, quality, and functional traits of the herbaceous layer. From this, the goals are to determine 1) how changes to the vegetation structure and composition influence perceived predation risk and the trade-off between risk and food availability for herbivores, 2) distribution and habitat use of predators, and 3) how these relationships might change as a result of increased woody cover due to climate change.
Single and mixed-species herding: mechanisms to offset predation risk
Off-setting predation risk is often considered to be a major goal of prey species. Two mechanisms prey can use to achieve this are forming large aggregations (dilution) or herding with other prey species (dilution and detection). The main goals of this research are to 1) gain a better understanding of how common savanna prey species can use dilution and detection to reduce their predation risk, 2) determine how this varies across a predation pressure gradient, and 3) explore the information-competition trade-off made by prey species.
The use of olfactory cues by mammalian herbivores
Herbivorous mammals face countless foraging decisions each day and must locate critical food resources among less favored options. One way herbivores can streamline this process is to rely on their sense of smell to hone in on favored food items. We are particularly interested in the role of olfactory cues and signals by herbivores to locate and discriminate between food resources and to signal resource defense. Our research on the use of olfactory cues is both experimental as well as observational.
The role of plant chemical defenses in dictating herbivore diet choice
We are interested in the interaction between plants and mammalian herbivores with respect to plant secondary metabolites (PSMs). There is a wide variety of PSMs, but the ones that have disruptive properties for large mammalian herbivores are the ones of key interest to us. We are most interested in what drives the diet selection of large mammalian herbivores, including African elephants and goats, because these two species are prominent in the African landscape and have large impacts on their ecosystems. To explore what motivates selection for particular species of woody vegetation, we use a combination of behavioral choice trials, physiological analyses of herbivore saliva, and explorations of plant chemistry using both traditional wet chemistry as well as measures of plant volatile emissions.