On the savannah, mixed company is good

It’s not uncommon for different species of wild animals on the African plains to hang out together, and now scientists have worked out why.

For many herbivores, it’s a matter of survival – they like to stay close to other species that sound the alarm when predators are lurking.

“A striking feature of the African savannahs are the ubiquitous mixed-species groups,” says senior author Jakob Bro-Jørgensen, from the University of Liverpool, UK.

Mingling occurs among many diverse groups including buffaloes (Syncerus caffer), zebras (Equus quagga), ostriches (Struthio camelus), warthogs (Phacochoerus africanus), antelopes (Chordata) and giraffes (Giraffa camelopardalis).

But understanding why competing species coexist – who mixes with whom, when and why – has long confounded ecologists, including Bro-Jørgensen, despite working with these animals for more than 20 years.

“Do species group with those that are best at spotting predators?” he wondered. “Or those that are most likely to be eaten instead of yourself should a predator attack? Are those who compete for the same food avoided?”

To explore these possibilities, he and colleagues created a theoretical model, published in the journal Ecology Letters, to determine which best explained patterns of social attraction among different species.

They then tested the model’s predictions in a community-wide field study of savannahs in the Masai Mara ecosystem, on the border of Kenya and Tanzania, using multi-layered network analysis.

Their findings confirmed recent theories that information sources, not just the location of food and predators, drive different animals to group together.

“African savannah herbivores seek out species with the most informative alarm calls as social partners,” says Bro-Jørgensen. 

Those who are less vigilant are more likely to join groups of other species, likely to compensate for their poorer ability spot predators, he explains.

Animals that are more vulnerable to predators were attracted to mixed-species groups, preferring to mix with those that have the same predators. However, when competition for food was intense, they tended to avoid species with similar diets.

These insights into the survival function of interspecies mingling have broader ramifications, particularly for the animals’ conservation.

“The impact of communication between species on social attraction and survival highlights the importance of taking behavioural, as well as ecological, links between species into account in order to understand how the natural world operates,” says Bro-Jørgensen.

“This in turn is crucial to uncover how animal communities respond to current environmental changes – declines in species occupying central positions in social networks, such as key informants, can lead to declines in other species throughout the ecosystem.”