The disappearance of megafauna, such as giraffes, from the savannas in East Africa could send ecological ripple effects throughout the landscape.
Much like the beneficial but complicated effects that the wolves of Yellowstone National Park exert upon their environment, recent research is beginning to show that there is a complex relationship between elephants, giraffes and other megafauna and their natural habitats, the African savannas.
What science demonstrates over and over again is that in nature, the threads between wild animals and the places that they naturally inhabit are convoluted. But overwhelmingly, there tends to be a reason why certain species are in a specific location: because there is a mutual benefit.
We’re also increasingly finding that allowing those species to freely live in those environments not only helps them and their landscapes but us, as well.
African elephants eat as much as 600 pounds of vegetation in one day. In comparison, a human adult eats about four pounds of food per day.
Creating refugia on steep slopes
Just as the feeding habits of wolves have brought back a wealth of diversity to the Western landscape in the United States, large animals, such as elephants and giraffes, are creating refugia for a wide array of life on the African savannas.
Megaherbivores spend the majority of their time trying to eat as much food as possible while expending the minimum amount of effort. For example, elephants may consume as much as 600 pounds of vegetation in a day; giraffes, about 75 pounds. In order to assess the impact these megaherbivores are having on vegetation across a range of landscapes in Africa, scientists from the Smithsonian Tropical Research Institute and collaborating institutions looked at foraging patterns in a savanna in Kenya.
At a monitoring plot located at Kenya’s Mpala Research Center, the researchers studied damage on Acacia mellifera trees, which are widely spread all over the savanna landscape and are a common meal for megaherbivores. The scientists found that large mammals preferred to eat their meals on flat ground, such as in plateaus and valleys. They adjust their movement patterns to avoid costly mountaineering; in other words, hilly or mountainous landscapes required too much expended energy when weighed against the food to be gained. Thus, the trees growing on steep slopes were taller than those in lower places. The number and variety of trees encountered on the steep slopes were higher, as well.
Acacia trees provide some of the only shade in many parts of Kenya. They also provide nesting sites for birds and insects, fix atmospheric nitrogen, and their excellent root systems help stabilize the soil.
The animals’ behavior did not change during the dry season, when resources become scarcer, indicating that elephants and giraffes would rather disperse to new areas with more favorable conditions than climb up a nearby slope to feed. Such feeding patterns may help preserve steep slopes as habitat refugia, with a greater diversity and density of vegetation than in more frequently browsed areas.
Favoring longevity in trees
But what seems like a contradiction comes from the results of a previous study, when researchers found that when protected from herbivores, some acacias in African savannas actually declined.
Fencing off areas of the trees at a study site in Kenya in 2008, Todd Palmer, an assistant professor of zoology at the University of Florida, and his colleagues discovered a mutualistic relationship between acacia trees and ants. The acacias provide food (in the form of nectaries) and shelter (at the base of the thorns on the trees) for three species of ants. The insects, in turn, offer the trees protection against pests, such as wood-boring beetles.
Giraffes favor eating the leaves and twigs of acacia trees. Although the trees are armed with big, sharp thorns to protect their juicy leaves from attackers, giraffes are able to use their long, maneuverable tongues and tough lips to get around them.
When elephants, giraffes and other large mammals could no longer graze on the acacias, the trees produced less nectar to support aggressively defensive ant species. Thus, ant colony size decreased and a less protective, fourth ant species became dominant over the others. The acacias then became vulnerable to scale insects and wood-boring beetles that made cavities that served as homes for the useless fourth species of ant. Overall, the researchers found that fenced trees were twice as likely to die as the unfenced ones, and they grew 65 percent more slowly.
So, completely ridding the acacias of the large mammals causes their hard-working “employees” to starve and grow weak, ironically making individual trees grow more slowly and die younger.
Checking disease transmission to humans
Not only do populations of unbeneficial ants increase without elephants and giraffes, so do fleas, mice, snakes and ticks.
Among the most productive grasslands on Earth, African savannas are threatened by human actions, such as conversion to agriculture, development, logging, overgrazing by livestock and the introduction of non-native plant species.
African savannas are among the most productive grasslands on Earth and host an abundance of wildlife. This productivity also makes them attractive to people who want to live there in order to raise their cattle, goats and sheep. As human populations increase, the needs of wildlife come into conflict with the needs of people and the livestock they tend.
In a 2014 study, scientists from New York’s Bard College and the University of California, Davis, experimentally removed large grazing mammals from plots of savanna land in Kenya, and a cascade of consequences followed: populations of a small mammal, the pouched mouse, doubled. The mice attracted venomous snakes, such as the olive hissing snake; devastated tree seedlings; and doubled flea and tick populations, which potentially increased the risk of transmission of flea- and tick-borne pathogens to humans.
The study confirmed that large mammals, such as giraffes, elephants and zebras, keep rodents in check, reducing the number of venomous snakes and the number of fleas that can transmit diseases. Large mammals also increased the survival of tree seedlings.
In Kenya, goats and sheep are very easy to rear. They can be comfortably kept on a small portion of land, providing meat, wool and high-quality skins for the leather industry. ©CTA ACP-EU, flickr
The researchers concluded that while the relationships among humans, livestock and wildlife are complicated, the negative impact of wildlife on livestock is often less severe than most people guess, mitigated by the beneficial decreases seen in rodent numbers. The study is proof that careful coordination between human needs and wildlife requirements is advantageous for both.
Saving ourselves
Throughout sub-Saharan Africa, large mammals are threatened by habitat fragmentation, human population growth, overhunting and other degradations.
Supporting antipoaching measures, rescue-rehab-and-release initiatives, “forever” sanctuaries, and programs that involve local people in conservation efforts are just a few of the steps we all can take right now to slow the loss of the planet’s megafauna and in the process, aid in protecting ecosystems—and our own health.
Here’s to finding your true places and natural habitats,
Candy
