Invasive insects can cause serious disruptions, including the extinction of native plants and animals, destruction of biodiversity, and permanent shifts in the ecosystems to which they spread. A new study shows how one tiny insect can have outsized impacts like these, even on predators thousands of times its size.
Research recently published in the journal Science investigated how the invasive big-headed ant is shifting predator-prey dynamics in Kenya’s Ol Pejeta Conservancy. Over three decades, scientists have been using tracking technology, hidden camera traps, mortality data, and statistical modeling to follow the impacts of this tiny insect, which has been introduced to the area through human activities.
They’ve found that the impacts begin with the native ant species, which have a mutually beneficial relationship with acacia trees. They nest within the trees but also protect them from larger herbivores that may want to use them for browsing.
Todd Palmer, study co-author and professor at the University of Florida’s Department of Biology, says, “Much to our surprise, we found that these little ants serve as incredibly strong defenders and were essentially stabilizing the tree cover in these landscapes, making it possible for the acacia trees to persist in a place with so many big plant-eating mammals.”
The big-headed ant, however, hunts these native ants and can decimate their numbers. As a result of their population impacts, the acacia trees are more vulnerable to big herbivores, like elephants, who reduce the cover the trees provide by eating more than they would if the native ants were still protecting them.
The change in vegetation extends beyond herbivores, to an iconic carnivore: the lion. Lions use the cover from acacia trees to hunt zebras and have much less success if they can’t stalk behind this vegetation. This has led to a shift in their targeted prey, as they’re eating more African buffalo. While this has not yet been found to impact the lion’s population, as the researchers say lions are able to find solutions to problems like this, it is something they plan to continue to study.
The team says the findings do show how a small invasive species can completely shift dynamics between much larger animals, but they hope some of these impacts can be mitigated.
Palmer explains, “These ants are everywhere, especially in the tropics and subtropics. You can find them in your backyard in Florida, and it’s people who are moving them around. We are working with land managers to investigate interventions, including temporarily fencing out large herbivores, to minimize the impact of ant invaders on tree populations.”