How little things rule the world

SUBTLE: INVASIVE ANTS CAUSE LIONS TO CHANGE DIET

You may have heard of the “butterfly effect”, but how about the “ant effect”? Research published on Thursday has shown how an ant muscled into a Kenyan savannah and sparked such a dramatic transformation in the landscape that even the local lions changed the way they hunt.

The study highlights the potentially profound impacts of invasive species, which are spreading at an increasing rate as human activities give animals, insects and plants opportunities to hitchhike into new territories.

“Oftentimes, we find it’s the little things that rule the world,” said Todd Palmer, an ecologist from the University of Florida, who was part of the research team that traced the implications of the big-headed ant on the hunting habits of lions in central Kenya.

It all starts with the whistling-thorn acacia trees in the plains of Laikipia, Kenya.

These thorny trees had developed a mutually beneficial relationship with the local acacia ant: The trees provide shelter and food for the ants and in return they use their stinging bite to discourage hungry elephants from devouring the trees.

But the big-headed ant changed all that.

Thought to have originated on an island in the Indian Ocean and brought to the area by the movement of people and goods, these invasive marauders arrived around two decades ago and started killing the acacia ants, leaving the whistling-thorn trees vulnerable to herbivores.

Diminished tree cover poses a problem for lions because they rely on the element of surprise to ambush their prey.

Researchers spent three years in Kenya’s Ol Pejeta Conservancy tracking the lions' movements with GPS collars to see how they responded in the areas colonised by the invasive ants.

Their study, published in the journal, Science, found that the big-headed ants had led to a threefold decline in zebra killings.

But the researchers were surprised to find that this did not cause the lion population to decline. Instead, the big cats switched dining preference and strategy – ganging up in larger groups to go after buffalo, said Douglas Kamaru of the University of Wyoming, lead author of the study.

While the lions have adapted thus far, the big-headed ants could spell trouble for other species that rely on the whistling-thorn tree, like giraffes or the critically endangered black rhino.

And the lions’ changing diet may provoke its own cascade of impacts.

“We don't yet know what could result from this profound switch in the lions’ hunting strategy,” Palmer said. –