Mixed-species group formation in response to multiple predators in the
South African savannahs
Abstract
The formation of mixed-species groups (MSGs) (also called heterospecific
or polyspecific groups) is often considered an anti-predator strategy
used in response to an increased predation risk. Recent studies
performed in savanna ecosystems in Africa have demonstrated an increased
formation of ungulate MSGs in higher predation risk areas. Nevertheless,
these studies only considered one predator species (the lion Panthera
leo) in evaluating the response to predation risk. Yet, species evolve
in multi-predator systems that require prey to respond to multiple
sources of risks. Although the importance of incorporating these
multiple predators in studies is recognized, there is still little
information on the behavioral strategies, including MSG formation, that
prey can use to minimize predation risk from multiple predators. In the
present study, we analyzed a large dataset of camera trap data (more
than 160,000 observations) from five sites located in savanna biome in
South Africa. We studied the likelihood of MSGs formation in response to
the presence of different predators (lion, leopard (Panthera pardus),
spotted hyena (Crocuta crocuta), and wild dog (Lycaon pictus)). We
demonstrated that the probability of forming MSGs increased when (i) the
photographic rate of the interacting species increased and (ii) the
photographic rate of predators increased. Our results showed that lion
and spotted hyena are the predator species most likely to trigger the
formation of MSGs for different prey species. These results suggest a
“hierarchy of fear” among predators in which both species are the most
feared, even for prey species that either predator does not
preferentially select. A large number of MSGs formed in the presence of
these two predator species included Burchell’s zebras (Equus quagga
burchellii), in association with species that have complementary modes
of predator detection (e.g. wildebeest (Connochaetes taurinus) and
giraffe (Giraffa camelopardalis). Our study highlights the importance of
incorporating multiple predators into MSG analyses to better understand
ecosystem functioning and, community formation.