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Hwange, Zimbabwe

Pays O.,University of Angers | Pays O.,Hwange Main Camp Research | Ekori A.,Hwange Main Camp Research | Ekori A.,University Claude Bernard Lyon 1 | And 2 more authors.

Prey can obtain valuable benefits from associating with other species if heterospecifics help to detect predators or locate good food patches. In mixed-species groups, how species respond to the presence of other species remains a poorly explored question although it might give crucial insights into mechanisms underlying the interspecific coexistence. We studied temporary mixed-species groups of large herbivores in Hwange National Park (Zimbabwe) between the common impala (Aepyceros melampus), the focal species here, and bigger species including the plains zebra (Equus quagga), the greater kudu (Tragelaphus strepsiceros) or the blue wildebeest (Connochaetes taurinus). In the Hwange savanna, the focal and smaller species are exposed to a larger range of predators than the associated species. In this context, we investigated how impalas adjusted their vigilance with group size comparing impala-only and mixed-species groups and whether the identity of heterospecifics affected vigilance of impalas. Our study showed that the time impalas spent in vigilance significantly decreased with group size when they formed impala-only groups, whereas it did not significantly vary with group size in mixed-species groups. Moreover, in mixed-species groups, impalas did not adjust their time spent in vigilance with the proportion of conspecifics and the identity of the associated species. Thus, the mechanism underlying the difference of impalas' behavioural adjustment of vigilance with group size between single- and mixed-species groups seemed to be related to the presence but not to the number and the identity of heteropecifics. Finally, we discuss the concept that larger and dominant heterospecifics were likely to increase competition for food access, thereby forcing higher vigilance of impalas, outweighing any reduction from collective vigilance. © 2014 Blackwell Verlag GmbH. Source

Pays O.,University of Angers | Blanchard P.,CNRS Biological Evolution and Diversity Laboratory | Valeix M.,University Claude Bernard Lyon 1 | Chamaille-Jammes S.,CNRS Center of Evolutionary and Functional Ecology | And 8 more authors.

Vigilance allows individuals to escape from predators, but it also reduces time for other activities which determine fitness, in particular resource acquisition. The principles determining how prey trade time between the detection of predators and food acquisition are not fully understood, particularly in herbivores because of many potential confounding factors (such as group size), and the ability of these animals to be vigilant while handling food. We designed a fertilization experiment to manipulate the quality of resources, and compared awareness (distinguishing apprehensive foraging and vigilance) of wild impalas (Aepyceros melampus) foraging on patches of different grass height and quality in a wilderness area with a full community of predators. While handling food, these animals can allocate time to other functions. The impalas were aware of their environment less often when on good food patches and when the grass was short. The animals spent more time in apprehensive foraging when grass was tall, and no other variable affected apprehensive behavior. The probability of exhibiting a vigilance posture decreased with group size. The interaction between grass height and patch enrichment also affected the time spent in vigilance, suggesting that resource quality was the main driver when visibility is good, and the risk of predation the main driver when the risk is high. We discuss various possible mechanisms underlying the perception of predation risk: foraging strategy, opportunities for scrounging, and inter-individual interference. Overall, this experiment shows that improving patch quality modifies the trade-off between vigilance and foraging in favor of feeding, but vigilance remains ultimately driven by the visibility of predators by foragers within their feeding patches. © 2011 Springer-Verlag. Source

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