OOS 46-9 - War and reconstruction in African savanna ecosystems: Large herbivores as ecological linchpins

Friday, August 11, 2017: 10:50 AM
Portland Blrm 253, Oregon Convention Center
Robert M. Pringle, Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ

How do African savanna ecosystems get the biological properties they have? How do they reconstitute themselves after being torn apart? And what can basic, curiosity-driven science tell us about how to manage their recovery — if anything? My talk is about the role of large mammalian herbivores — the megafauna — in these processes. I will discuss the factors that shape the dietary choices of these animals, and how their foraging decisions shape large-scale ecosystem properties such as the diversity and distribution of tree species. Lastly, I will examine the effects of human warfare on African savannas, focusing in particular on one war-torn ecosystem, Mozambique’s Gorongosa National Park. Wildlife populations are highly sensitive to armed conflict, and the >90% declines of Gorongosa's large-mammal populations during the Mozambican Civil War (1977-1992) triggered profound ecological changes throughout the park. Yet Gorongosa’s history is also a testament to nature’s resilience. I will illustrate how our ever-improving understanding of species interactions has helped to steer the ongoing rehabilitation of one of Africa’s most spectacular protected areas.


Selective herbivory by large mammals interacts with abiotic factors such as soil properties to create habitat specificity and beta-diversity in savanna tree communities. However, we know surprisingly little about "selective herbivory" -- i.e., dietary choices -- of free-ranging wild large herbivores. DNA metabarcoding reveals a remarkable degree of dietary niche partitioning at the level of plant species in diverse large-herbivore faunas. These insights have guided the investigation into postwar ecological recovery in Mozambique's Gorongosa National Park. The collapse of the large-herbivore fauna was associated with ecosystem-wide shifts in woody cover and understory species composition; field experiments showed this to be the result not of collapse per se, but of the subsequent irruption of a single species of selectively feeding medium-sized antelope. High-resolution dietary analysis further supported this hypothesis, and also showed that recovering herbivore populations were feeding most heavily on an invasive woody shrub. This discovery suggests that a "natural solution" to invasvie plant management will simply be to allow native large-herbivore populations to recover, rather than undertaking aggressive pesticidal measures.