The influence of large wildlife subsidies in the Mara River, Kenya

Much of my research tests fundamental questions about the influence of animal movements on ecosystem function, particularly through nutrient cycling within ecosystems and nutrient translocation across systems. I have been studying the influence of large wildlife on nutrient translocation from terrestrial to aquatic systems in the Mara River, Kenya, since 2010. The Mara River runs through the Maasai Mara National Reserve, Kenya, and Serengeti National Park, Tanzania, and sustains a large population of native wildlife.

The Mara is home to over 4,000 hippos, which graze in the grasslands at night and return to bask in the river during the day, and the Serengeti wildebeest migration, which crosses the Mara River multiple times in the northern portion of its range, occasionally resulting in mass drownings. I am working with Chris Dutton and David Post (Yale), and Emma Rosi and Steve Hamilton (Cary Institute) to quantify resource inputs to the river by hippos and wildebeest, and to ask how variations in quantity, stoichiometry and timing of these inputs interacts with discharge to influence food web structure and ecosystem function. We have received funding for this research from the National Geographic Society (2012-2013) and the National Science Foundation’s Ecosystem Program (2014-2018) and Population and Community Ecology program (2018-2021).

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Pablo’s hippos – invasive hippos in the Magdalena River, Colombia

Pablo Escobar imported four hippos into Colombia for his private zoo, but after his death, they escaped into the nearby Magdalena River. Anecdotal evidence suggests there may now be as many as 40-60 individuals, and they have been spotted up to 250 km away. Hippos have the capacity for a high annual growth rate; they are known ecosystem engineers that can modify their environment; and they are the deadliest animal in Africa. All of these characteristics suggest this may be the incipient stage of a species invasion with profound impacts

for the people and native flora and fauna of the Magdalena River. I am working with Beth Anderson (FIU), Suresh Sethi (Cornell), and Germán Jiménez (Universidad Javeriana), with funding from the National Geographic Society, to develop a population model for this species to understand their future population growth in response to potential management strategies and to study the coupled natural and human dynamics that may be influenced by this introduction.

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Use of inland, seasonal wetlands by American alligators

Isolated, seasonal wetlands are critical habitats for biodiversity in the southeastern U.S., yet they are not protected under the Clean Water Act. I am working with Lora Smith (Jones Center at Ichauway) to study the role of American alligators in the ecology of seasonal wetlands. Our research has shown that alligators provide biological connectivity between seasonal wetlands and riverine systems. Adult females use the wetlands as nesting and nursery sites, sub-adults disperse into nearby riverine systems once they reach a certain size, and adult males stay in riverine systems. I am working with  Carla Atkinson (UA) and Stacey Lance (SREL) to use stable isotopes and microsatellite data to better understand the spatial and temporal scale of this connectivity. We are also interested in studying the role of alligators as ecosystem engineers within the wetlands, as they dig potentially large and complex burrows that may extend the hydroperiod of the wetland and provide aquatic refugia for other species.