Animal migrations and resource subsidies influence river ecosystem dynamics

ABS Seminar, Co-hosted with Ecology and Evolutionary Biology

Presented by Dr. Amanda Subalusky, Postdoctoral Associate, Yale University

Animal migrations can play an important role in moving resources across ecosystem boundaries, and these resource subsidies can strongly influence food web structure and ecosystem function. In the Mara River, East Africa, large animal migrations provide substantial portions of the river’s carbon and nutrient budget through resource subsidies from the surrounding savanna grasslands. The river’s population of over 4,000 hippos contribute 13,200 tons of dung to the river every year through daily feeding migrations. The largest remaining overland migration of ~1.3 million wildebeest contribute 1,100 tons of carcass biomass through seasonal mass drownings during annual reproductive migrations. These inputs interact differently with river discharge to have important and complex impacts on the river. Hippo dung deposits on the river bottom during low flows, driving high rates of ecosystem respiration and providing an important resource to the river food web. Wildebeest carcasses have minor effects on river metabolism, but they provide an important resource to the river food web that persists for years through the slow decomposition of bones. Research in this system highlights some of the under-appreciated influences of animal migrations on river ecosystems.