Abstract
Mixed mammal species groups are common in East African savannah ecosystems. Yet, it is largely unknown if co-occurrences of large mammals result from random processes or social preferences and if interspecific associations are consistent across ecosystems and seasons. Because species may exchange important information and services, understanding patterns and drivers of heterospecific interactions is crucial for advancing animal and community ecology. We recorded 5403 single and multi-species clusters in the Serengeti-Ngorongoro and Tarangire-Manyara ecosystems during dry and wet seasons and used social network analyses to detect patterns of species associations. We found statistically significant associations between multiple species and association patterns differed spatially and seasonally. Consistently, wildebeest and zebras preferred being associated with other species, whereas carnivores, African elephants, Maasai giraffes and Kirk's dik-diks avoided being in mixed groups. During the dry season, we found that the betweenness (a measure of importance in the flow of information or disease) of species did not differ from a random expectation based on species abundance. In contrast, in the wet season, we found that these patterns were not simply explained by variations in abundances, suggesting that heterospecific associations were actively formed. These seasonal differences in observed patterns suggest that interspecific associations may be driven by resource overlap when resources are limited and by resource partitioning or anti-predator advantages when resources are abundant. We discuss potential mechanisms that could drive seasonal variation in the cost-benefit tradeoffs that underpin the formation of mixed-species groups.
Highlights
Group living in animals has attracted extensive attention in behavioural, ecological and evolutionary studies and is thought to have evolved from trade-offs between fitness relevant costs and benefits [1,2,3,4,5,6]
Such mixed species groups have long been recognized in a variety of animal communities: mixed species groups have been described in fish communities [14,15,16], avian assemblages [17,18,19] and in marine and terrestrial mammals [20]
Consistent association patterns across ecosystems or seasons were found for plains zebra – cape buffalo, plains zebra - Grant’s gazelle, plains zebra - Thomson’s gazelle, impala - vervet monkey and vervet monkey - blue monkey (TME during wet and dry season, p: 0.0004–0.021), and impala - topi (SNE during wet and dry season, p: 0.001–0.005)
Summary
Group living in animals has attracted extensive attention in behavioural, ecological and evolutionary studies and is thought to have evolved from trade-offs between fitness relevant costs and benefits [1,2,3,4,5,6]. A special case of group living occurs if individuals of different species form a group. Such mixed species groups have long been recognized in a variety of animal communities: mixed species groups have been described in fish communities [14,15,16], avian assemblages [17,18,19] and in marine and terrestrial mammals [20]. Among mammals, mixed species groups have been extensively described in primate communities [21,22,23,24] and in cetaceans [25,26,27]. Mixed species groups are associated with similar costs and benefits as single species groups. As a result of these three aspects, group size tradeoffs may be altered in mixed-species groups possibly leading to group size differences in single- versus mixed-species groups
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