Big-headed invasive ants disrupt lion predation of Kenya’s zebras

The Independent newspaper reports on a study which concluded that a big-headed invasive ant species has taken hold at 1,600 locations from East Africa to southern American states. It’s a remarkable story of an invasive species. Please note that species of all kinds become invasive because humans carry them to their new homes. We have to be careful in criticising invasive species such as the domestic and feral cat because the cat has been transported all over the world by human traders.

What is an invasive species? Answer: they are non-native species that have colonised a new area to the point of damaging the surrounding environment.

Two useful tags. Click either to see the articles: Toxic to cats | Dangers to cats

To return to these amazing ants. They appear to be very dominant because we are told that they kill native ants, and cut them up. Research has been carried out by the University of Wyoming on their impact on a wildlife conservation area in Kenya’s Laikipia County called Ol Pejeta.

….we show that the invasive big-headed ant (Pheidole megacephala) makes lions (Panthera leo) less effective at killing their primary prey, plains zebra (Equus quagga). Big-headed ants disrupted the mutualism between native ants (Crematogaster spp.) and the dominant whistling-thorn tree (Vachellia drepanolobium), rendering trees vulnerable to elephant (Loxodonta africana) browsing and resulting in landscapes with higher visibility.

Douglas N. Kamaru an team

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Lion predation disrupted

The presence of these ants has disrupted lion predation on the zebra as follows. In the region studied, the native acacia ants have a symbiotic relationship (both species benefit) with a dominant species of tree called the whistling-thorn tree.

The tree provides the ants with food in the form of nectar and shelter and the ants provide the tree with protection from herbivores by depositing formic acid on the trees and biting the herbivores. This works well against elephants as well as zebras.

But the invasive ants killed the native species and so many whistling-thorn trees were no longer protected allowing elephants to overgraze the trees. They became chewed up and broken. The rate of degradation of these trees was assessed as being 5 to 7 times faster than in those areas where there were no invasive ants.

With these trees being degraded, the landscape became barer. The lions had less cover which they sometimes depend on to stalk prey effectively including zebras.

This protected the zebras as the study found that lion predation on zebras was three times higher where there were no invasive ants compared to where invasive ants had taken hold.

The lion population didn’t decline because they turned their attention to the African buffalo as a prey animal as they were then deterred from preying on the zebra. The African buffalo is a much more difficult animal to kill.

Increased predation on buffalo

The study scientists found that over 20 years there was a 42%-67% drop in predation on zebras by lions in the area where there were these invasive ants while the number of buffalo killed jumped from 0% to 42%. Comment: this must also have affected the survival of the lion because lions can be killed when they try and kill a buffalo.

The research was led by a PhD student, Douglas Kamaru, who said that “a tiny invader reconfigured predator-play dynamics among iconic species”. It is speculated that it may affect the dynamics of lion prides in this park.

The invasion of these big-headed ants continues.

The study referred to is: Disruption of an ant-plant mutualism shapes interactions between lions and their primary prey. Link: https://doi.org/10.1126/science.adg1464

Big-headed ants

A team from the University of Illinois has done some work on the big-headed ant, which is considered to be one of the world’s most invasive species. The label includes soldier ants. Their heads are disproportionately large. They have an increased biting power in their mandibles.

When they encounter ants that fight back, they produce even larger headed ants to counteract the threat.

They can only tolerate warm weather but where they are invasive, they “spell doom for native ants, spiders and beetles and other invertebrates that are unaccustomed to their brand of warfare”.

They are considered one of the most problematic invasive species. The lead author said that “They are very aggressive. And unlike a lot of native ants, they produce large numbers of queens, so they have incredibly high potential for reproduction.”

Wikipedia picture of the ant: by the photographer and www.AntWeb.org, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=8116564

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