Invasive species
Kenyan lion hunting is hampered in 'ecological chain reaction' as big-headed ants fail to stop elephants from cutting down acacia trees – the cats' ambush site
When a lion decides to hunt a zebra, it seems like nothing can stop him. But now researchers have discovered that these giant predators are being thwarted by a tiny enemy: ants.
Scientists have found that the spread of large-headed ants in East Africa is creating a situation that is causing lions to kill fewer zebras.
Prof. Todd Palmer of the University of Florida, co-author of the study, said the results were a surprise. “I was stunned,” he said. The reduced killings appear to be because a crucial relationship between native ants and the trees they live in has been upended, leaving the lions without cover.
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 is the interactions that form the glue that holds the entire system together.”
Acacia ants protect whistling thorn trees by biting and stinging elephants in search of a snack. In return they receive nectar and protection. But big-headed ants — an invasive ant species that can take over whistling thorn trees by killing adult acacia ants and eating their eggs and larvae — offer no such protection.
“In invaded areas, elephants graze and break down trees five to seven times as quickly as in uninvaded areas,” Palmer and colleagues write in the journal Science.
To uncover the broader ecological impacts, Palmer and colleagues first examined a series of plots in Laikipia, Kenya, some of which contained elephants but others which were excluded.
The team found that when big-headed ants and elephants were present, there was a decrease in tree cover and a dramatic improvement in visibility.
The researchers then created a computer model based on observations in the wild to examine whether the presence of large-headed ants and increased visibility affected the zebras' movements, the zebras' kill locations, and the lions' movements.
The team found that killing zebras was almost three times more likely in low-visibility areas where large-headed ants were absent than in high-visibility areas where large-headed ants were present. However, the analysis ruled out a link to zebra density or lion activity, suggesting that the decline in killings is likely due to the lions becoming more visible to their prey
“Because lions need cover to successfully pursue and ambush their prey, they are at greater risk when there are fewer trees to hide behind, which appears to make it more difficult for them to successfully take down the zebra.” said Palmer.
While researchers say lion populations currently appear to be stable – apparently a result of lions switching from primarily killing zebras to hunting buffalo – Palmer said one concern is that there is no way to stop the spread to stop big-headed ants.
“This means that if the invasion continues, more and more acacia trees will be lost,” he said. “And since acacia trees are an important food source for many species, including rhinos and giraffes, these landscape-level changes could alter the ecology of the area quite dramatically.”
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