Collaborative Research: Feedbacks among Ecosystem Engineers and their Influence on Ecosystem Functioning

The spatial organization of landscapes is a major determinant of how ecosystems function and how many species they support. Understanding how such organization emerges, and how it affects biodiversity and processes such as carbon storage and nutrient recycling, is thus a key theme in ecological research and management. Animals that act as ‘ecosystem engineers’ by modifying the environment are major causes of spatial variation.

When multiple engineering species co-occur, each may regulate the behavior and impacts of the other; in this case, the properties of the ecosystem may depend on the interplay between engineers. The goals of this research are to understand how ecosystem engineers interact, how they influence ecosystem organization and function, and how these processes depend on human activity.

The project focuses on two influential species at opposite ends of the body-size spectrum: white rhinoceros (one of the biggest land animals, which modify vegetation by grazing and transporting nutrients across landscapes) and termites (which boost plant growth by decomposing organic matter and altering soils) in South Africa’s Kruger National Park. There, the world’s largest population of white rhinoceros occupies a landscape with numerous patchily distributed termite colonies and varying levels of risk from poachers.

By tracking rhino behavior, experimentally excluding rhino and/or termite activity, and building detailed 3D landscape maps, the research will give insight into how feedbacks between engineers regulate plant growth and nutrient cycling, and whether the threat of poaching disrupts these processes. Because ecosystem engineers occur worldwide (e.g., prairie dogs, beaver, and bison in North America), knowledge produced through this project will be widely applicable to environmental management.

The project will also advance understanding and conservation of white rhinoceros, which are threatened with extinction. Finally, the project will train early-career scientists and engage K-12 school audiences and the public through field- and museum-based programs in the United States and South Africa, deepening public understanding of ecosystem science and the important roles played by animals both large and small.

Researchers will use surveys, exclusion experiments, GPS tracking, hormonal assays, and fecal DNA and nutrient analysis together with high-resolution drone-based remote sensing to measure feedbacks between mega-grazers (white rhino) and soil-dwelling decomposers (fungus-farming termites); how these feedbacks create and maintain heterogeneity, regulate ecosystem functions (productivity, decomposition, nutrient transport, nitrogen mineralization), and affect biodiversity; and whether risk of predation (poaching) alters these feedbacks by modifying rhino behavior and abundance. Specifically, data will be analyzed to test: (1) How do termites affect the movement, diet, and behavior of white rhino, and how does that affect nutrient redistribution? (2) How does rhino activity reciprocally alter termite distribution, and how does this feedback loop affect the spatial organization of species and nutrient cycles? (3) How does human pressure affect rhino behavior and physiology, and does this disrupt the rhino–termite feedback and thus diminish the ecological role of mega-grazers?

By working across areas that differ in geology, climate, and poaching risk, the researchers will also evaluate how and why such multi-engineer feedbacks depend on environmental context. Conceptually, the project advances the study of ecosystem engineering by linking it to theories of consumer-resource dynamics and ‘landscapes of fear’.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.