Reversing defaunation through rewilding and its consequences for biodiversity and ecosystem function

Supervisor: Professor Rob Fletcher

The world is facing several global challenges that are transforming natural environments. One key challenge is that the loss of animals, or ‘defaunation’, has proceeded rapidly across the planet, impacting ecosystems and society. Returning species to ecosystems, or ‘rewilding’, is gaining increasing interest to combat this biodiversity loss, but our fundamental understanding of how animal communities and ecosystems reassemble remains limited. This project will integrate ecological theory and applied conservation to address outstanding issues in defaunation and rewilding by leveraging a long-term experiment in a South African savanna. We will address the following questions: Does defaunation alter remaining biodiversity and ecosystem function? What are the mechanisms that enhance the success of rewilding of herbivores? To what extent does rewilding reverse the effects of defaunation? The results from this project will identify the effects of the loss of large mammalian herbivores, such as savanna elephants, kudu, and impala, on remaining biodiversity and ecosystem functioning, the extent to which rewilding can reverse the effects of species losses on ecosystems, and whether rewilding of large mammals is sufficient to recover key processes that megafauna have long provided to ecosystems.

Type of work 

The student will become a critical member of a collaborative group that is working at the interface of applied ecology and conservation. The student is expected to do ecological field research in Kruger National Park, including field experiments on ecosystem function as large herbivores are experimentally excluded and then reintroduced into the study area. Finally, the student will apply models to experimental and observational data to rigorously test the diversity and magnitude of impacts of defaunation and rewilding.

Importance of the area of research concerned 

Rewilding is an important strategy for combatting the biodiversity crisis. However, little is known about the extent to which rewilding can reverse the impacts of defaunation it is designed to counteract.

References 

McCleery, R. A., L. Kruger, A. Monadjem, D. Tye, P. Mhlava, E. Zwane, A. Bijl, M. Jones, J. Hartfelder, M. Sibiya, C. Coetsee, and R. J. Fletcher, Jr. 2025. Megaherbivores facilitate large grazing herbivores and suppress small mammals through vegetation structure and cryptic pathways. Biological Conservation 310:111378. Jones, M., R. J. Fletcher, Jr., L. Kruger, B. Wigley, C. Coetsee, A. Bijl, M. Mohlala, I. L. Zwane, and R. A. McCleery. 2025. Mega- and large herbivores influence survival but not recruitment rates of African savanna trees. Biological Conservation 308:111201.