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Termites Help Build Savanna Societies

The great animals of the African savanna may owe a debt of gratitude to the humble termite. New research reveals that the dirt mounds the insects build sustain significantly more shrubs, fruit-bearing trees, bugs, and animals, such as elephants, cheetahs, and zebras, than do surrounding areas. It's a “very satisfying demonstration” of how the termites “support an entire ecosystem,” says physiologist Scott Turner of the State University of New York College of Environmental Science and Forestry in Syracuse who has studied termite mounds in Namibia.

Most of the African savanna is comprised of stiff, dry dirt, but every 50 meters or so you'll come across a foot-high mound covered in green grass. African termites (Odontotermes) can spend centuries creating the mounds. Like earthworms on farmland, the termites aerate the surrounding soil, allowing more water to penetrate. Scientists knew that this activity, along with termite droppings, creates highly fertile patches of earth with a higher percentage of nitrogen and phosphorous than ground farther away. Such conditions invite the growth of grasses, shrubs, and trees. But just how much of an impact do these termites have on their ecosystem?

To find out, researchers conducted field surveys and developed simulations of the savanna. They found that acacia trees, which dominate this landscape, grow 60% more new shoots near termite mounds and are more than twice as likely to bear fruit as those far away. The acacias and other plants attract insects: When the researchers set up sticky traps to collect beetles, flies, and other bugs, the side of each trap that faced the mound-collected 40% more insects than the side facing away. These insects, in turn, draw in larger animals, such as geckos. Geckos were more than twice as likely to be found on trees near mounds than on those far away, the researchers report today in PLoS Biology.

The relatively high amount of grass on and near the mounds is also a magnet for large animals. Grazers such as zebra and buffalo congregate in these spots, fertilizing them further with their dung, says one of the paper’s co-authors, community ecologist Todd Palmer of the University of Florida, Gainesville.

Even the way the termites organize their mounds likely affects the savanna ecosystem, the team found. The insects space their mounds 20 to 120 meters from one another in a regular “polka dot” pattern across the landscape. Such a pattern maximally utilizes the savanna’s resources and attracts far more plants, insects, and gecko communities than randomly spaced mounds, according to a computer simulation run by the team.

Turner points out that African farmers often try to eradicate these termites, which they believe compete with cattle for grasses. He hopes the new work will help convince farmers that it's better to keep the termites around.

*This article has been corrected. A previous version of this article stated that termite mounds have far reaching effects on large animals such as elephants and cheetahs. The paper provides no evidence for these claims and they have been removed.