When a lion decides to chase a zebra, nothing seems to be able to stop it. But now researchers have discovered these enormous predators are thwarted by a tiny enemy: ants.
Scientists have found the spread of big-headed ants in the east Africa causing a situation that results in lions killing fewer zebra.
Prof Todd Palmer of the University of Florida, a co-author of the research, said the findings were a surprise. “I was amazed,” he said. The fewer deaths appear to be due to the restoration of an important relationship – between native ants and the trees they live in, causing a loss of cover for lions.
Palmer said the discovery highlights the importance of interactions between species. “We often talk about conservation in the context of species,” he said. “But it’s the interactions that are the glue that holds the whole system together.”
Acacia ants protect whistle thorn trees by biting and stinging elephants looking for a snack. In return, they get nectar and shelter. But big-headed ants – an invasive ant species that can take over whistle thorn trees by killing adult acacia ants and eating their eggs and larvae – offer no such protection.
“In invaded areas, elephants browse and break trees at five to seven times the rate of those in uninvaded areas,” Palmer and colleagues writing in the journal Science.
To extract the wider ecological impacts, Palmer and colleagues first studied a number of plots in Laikipia, Kenyasome where elephants were present, some where they were excluded.
The team found that when big-headed ants and elephants were present there was a drop in tree cover and a dramatic increase in visibility.
The researchers then built a computer model based on observations in the wild to investigate whether the presence of big-headed ants and increased visibility affected zebra movements, zebra kill sites and the movements of lions.
The team found that zebra kills were nearly three times more likely in low-visibility areas where big-headed ants were absent than in high-visibility areas where big-headed ants were present. But the analysis ruled out a link with zebra density, or lion activity, suggesting the decline in deaths is likely because the lions are more visible to their prey
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“Because lions need cover to successfully stalk and lure their prey, they are more exposed when there are fewer trees to hide behind, which seems to make it more difficult for them to successfully take down the zebra,” Palmer said. said.
While the researchers say lion populations currently appear to be stable — apparently a result of lions shifting from mainly killing zebras to hunting buffalo — Palmer said one concern is that there is no way to stop the spread of the big-headed ants.
“What this means is that if the invasion continues, more and more acacia trees will be lost,” he said. “And because acacia trees are important food for many species, including rhinos and giraffes, these landscape-level changes can alter the ecology of the area quite drastically.”
