In March 2024, in the middle of Novalee Sweeney’s first trip to South Africa’s Kruger National Park, the Marquette microbial ecology doctoral student stumbled into the middle of both a tragedy and an opportunity. While returning to camp, she and other members of an international research team encountered a group of park rangers gathered around the body of an elephant, which they had made the decision to shoot and kill because it was too injured to walk.
An elephant’s death can be sorrowful and dramatic. For Sweeney and her colleagues, including Dr. Nathan Lemoine, assistant professor of biological sciences, it also represents the beginning of a different, and still largely mysterious, process. When an elephant dies on the savannah its body offers a bounty of nutrients to nearby life, fostering a cycle that can last for years, feeding plants, insects and animals. On that day in March, the recently deceased animal represented an opportunity to study this process from the very beginning.
Lemoine is part of the Megacarcass Ecology Working Group, or MEWG, an international collaboration of researchers working to understand how large animals such as elephants affect the savannah after they die and begin to decay. It’s a phenomenon that has been studied in whales — which can spawn entire ecosystems after they die and fall to the seafloor — but never before in large land animals.
“When a whale falls, it’s the only thing there,” Lemoine says. “An elephant is dying in this bigger matrix of a grassland with resources and a healthy ecosystem around it.”
Lemoine, a co-principal investigator of MEWG, as well as one of its founding members, is an ecologist who studies how rapid global change — generally human generated — is affecting ecosystems. As megafauna like elephants dwindle, their absence will have ripple effects on the ecosystems they participate in. Put more bluntly, without elephant carcasses, the savannah may not function the same; Lemoine is there to find out exactly how.
It’s a question Lemoine has spent three field seasons at Kruger working to answer, with support from a $1.4 million research grant from the National Science Foundation, $460,000 of which funds the work of the Marquette team. Building on work by Dr. Deron Burkepile, another project PI and Lemoine’s Ph.D. adviser, he has traveled to South Africa each year to track the evolution of an ever-growing list of elephant carcass sites.
Now in its fifth year, the project has cataloged more than 60 elephant carcasses in Kruger National Park, which encompasses over 7,500 square miles of savannah. The work entails long, arduous days of driving, hiking and scrupulously documenting elephant carcass sites, typically two or three each day. Working alongside expert game guards from the park, team members gather soil samples, catalog plant and animal species, note the locations of bones, and leave behind cameras to keep an eye on the sites.
This is some of the first work of its kind done anywhere on land, Lemoine says, meaning most discoveries the team makes are brand new, and of great interest to other scientists around the world studying plants, animals, ecosystems and more.
Studying life after death
Lemoine has found that, from an ecosystem perspective, a dead elephant is something like a fertilizer bomb, dropping a huge amount of ammonium and other chemicals onto a single location in the savannah. These compounds, essential for plant growth, are so concentrated near the carcass that they’re actually toxic to most plants. That leaves an opening for two species, Urochloa trichopus, or bushveld signal grass, and Megathyrsus maximus, also called Guinea grass or green panic grass, which can tolerate the high levels of ammonium.
Free from competition, these two species colonize carcass sites in the years after an elephant dies, creating what Lemoine calls a “grazing lawn” dense with luscious grasses. The abundant plant life attracts herbivores such as zebra, greater kudu and impala, which in turn deposit more nutrients through their dung and urine, allowing yet more forms of life to move in. In this way, a single elephant creates a self-sustaining micro-ecosystem that persists for years. “If you want to enumerate the economic value of a living elephant, then it goes for far longer than the elephant is alive,” Lemoine says.
A forthcoming documentary, “The Legacy of Megaherbivores,” will follow the life and death of an elephant in the African savannah, explaining its effect on ecosystem function. It will also explore the work of Lemoine and colleagues, who collaborated closely with filmmaker Tom Bouyer.
Lemoine’s work is already showing that megacarcass sites can evolve very differently depending on scavenger activity. In the scavenger-rich south of the park, Lemoine says an elephant’s remains can largely disappear in just weeks. In the park’s north, where scavengers are few, the bones can stick around for years. Other data from cameras left at the sites shows elephants returning to sites to move skulls around, even tearing out rebar placed by the researchers to mark the area. “They really don’t like having their dead friends messed with,” Lemoine says.
While Lemoine is focusing on the big-picture ecological changes that happen at elephant carcass sites, other team members, including Sweeney, are zooming in on the specifics. Sweeney is working to take a census of grasshoppers near the carcasses, while other researchers are gathering soil samples to compare microbial populations at the sites to those elsewhere. In the future, Lemoine hopes to expand the team’s work to termite mounds, wildflowers, pollinator activity and more.
Understanding the “ensmallment of the world”
Their research is taking place against a global backdrop of declining and endangered animal populations, a trend that is having effects that spread far beyond the animals themselves, the researchers say. Large animals such as elephants, rhinoceroses and bison move nutrients around and between ecosystems, and when they die, provide crucial islands of life that together could add up to a significant impact. Now, their numbers are diminishing, leading to what Lemoine calls the “ensmallment of the world.” The implications of that development are still unclear.
In addition to being a first-of-its-kind research project that’s bringing new knowledge to the international scientific community, the project has been good for both Marquette and the people who work there, says Michelle Budny, the lab manager for the Lemoine Lab. “This is something that’s incredibly valuable and has brought a lot of value to the department and the university,” she says.
Continuing the project gives students like Sweeney important field experience, and lets Marquette researchers connect with colleagues from around the world, Lemoine says. The working group is now discussing expanding the project to rhinoceroses soon, as well as to Mpala Research Centre in Kenya, a much drier environment, to study megacarcass ecology there.
Meanwhile, the teams are returning year after year to sites they’ve visited in past years, watching each microcosm develop and grow. Each represents the legacy of a single elephant whose physical form has vanished but whose influence lives on in the nearby grass, insects and animals — and in the future of the savannah itself.
