Doctors often warn humans to lower their sodium intake, but a new study led by Hunter College researchers shows that Earth’s largest land animals struggle to find enough salt to survive.
A study published December 9 in Nature Ecology and Evolution shows the populations in Africa of the largest land animals — the so-called megaherbivores such as elephants, giraffes, zebras, and rhinos — appear smaller than one might expect because of salt limitations. The density and distribution of megaherbivore populations lag despite the presence of abundant greenery across Africa, including in Kenya, Uganda, South Africa, and Republic of Congo.
“West Africa is a very productive region,” said Professor of EcoInformatics at Northern Arizona University Chris Doughty, a study coauthor. “Even so, there aren’t many megaherbivores there. We think that a lack of sodium, likely combined with other factors such as overhunting and soil infertility, plays an important role in limiting their numbers.”
The authors found that the nutritional challenge shows up in the plants of the continent.
“In Africa, sodium availability varies more than 1,000-fold in plants,” explains the study’s lead author, Andrew Abraham, who is now a research associate at Hunter College’s Wildlife Nutrition Research Group. “This means that, in some areas, wild herbivores simply cannot get enough salt in their diet.”
Salt limitation drives some extreme behavior in the wild.
“Some animals will go to great lengths and use unusual resources to obtain sodium,” said Hunter Anthropology Professor Jessica Rothman, a co-author of the study.
To find the rare nutrient, they go spelunking and salt mining in a fashion.
“In Kenya, elephants enter caves to consume the sodium-rich rocks,” Abraham said. “In Congo they dig for salt in riverbeds.”
Not just elephants. Gorillas fight for the saltiest foods, while rhinos, wildebeests, and zebras often gather at salt pans in the Kalahari Desert.
The authors combined high-resolution maps of plant sodium with databases of animal dung and density measurements.
“Dung can provide important insights into animal nutrition” said Hunter Postdoctoral Associate Celeste Maré, another co-author. “Feces can tell us if animals have enough sodium in their diets.”
The research raises a number of important conservation concerns. Animal preserves may not contain enough of the vital nutrient — drawing animals into conflict with humans as the animals seek salt in human habitats.
“Many protected areas are located in low-sodium environments,” Abraham noted. “But humans have also created artificial sodium hotspots through various activities, including borehole pumping and road salting. If animals can’t get enough sodium in their natural habitats, they may come into conflict with people on their quest to satisfy their salt hunger.”
Today, humans live in a world abundant in salt. It’s easy to overlook that this everyday seasoning often isn’t available for wild animals. Remember that next time you reach for the saltshaker.
