Current Research Projects

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

img_4001Much 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-Marshall (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 also are collaborating with Jonas Schoelynck and Erik Struyf (U of Antwerp) to ask how hippo inputs may influence silica cycling in the river. We have received funding for this research from the National Science Foundation’s Ecosystem Program (2014-2017) and National Geographic Society.

Paleoecological approaches to understanding the historical context of the Mara Basin

The825 Mara River Basin drains one of the most iconic conservation areas in the world – the Serengeti Mara Ecosystem – but much remains unknown about the historical context of this basin,
how current ecosystem dynamics and rates of change compare to historical levels, and the effectiveness of conservation measures in the upper catchment. In 2015, we received funding from WWF to use sediment cores from the Mara Wetland, where the Mara flows into Lake Victoria, to begin answering these questions. I am working with Chris Dutton, David Post, Carla Staver and Julie Aleman (Yale), and Troy Hill (EPA), to analyze historical vegetation communities, fire regime and wildlife abundance in the basin; ask how anthropogenic development in the basin has influenced sediment sources and mercury and nutrient levels in the river; and estimate the impact of conservation measures in the Mau Forest over the last two decades.

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

Pablo Es506cobar 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 40-50 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), with funding from the National Geographic Society, to conduct a first population survey of hippos in the Magdalena, and to study the coupled natural and human dynamics that may be influenced by this invasion.

Use of inland, seasonal wetlands by American alligators

gator burrow

Isolated, seasonal wetlands are critical habitats for biodiversity in the southeastern U.S., yet they are not protected under the Clean Water Act. During research for my Master’s degree, I worked with Lora Smith (JERC) and Lee Fitzgerald (TAMU) to show that American alligators in the inland portion of their range provide biological connectivity between seasonal wetlands and riverine systems. I used trapping, surveys, and radio telemetry to show that 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 continuing to work with  Carla Atkinson (UA) and Stacey Lance (SREL) to use stable isotopes and microsatellite data to better understand the spatial and temporal scale of the connectivity.