Animal Vigilance: Monitoring Predators and Competitors by Guy Beauchamp

Author:Guy Beauchamp [Beauchamp, Guy]
Language: eng
Format: epub
ISBN: 9780128019948
Publisher: Elsevier
Published: 2015-09-15T00:00:00+00:00

5.3.3. Recent Developments

Here, I explore two recent developments that have challenged some of the traditional assumptions made in models of anti-predator vigilance.

5.3.3.1. Temporal Variation in Predation Risk

To document the group-size effect on vigilance, researchers need to measure vigilance in groups of different sizes. As explained earlier, it is possible to manipulate group size directly or to document vigilance opportunistically in different groups as they are encountered. Animals are expected to adjust their vigilance depending on the size of their current group. A recent model suggested that variability in group size across time could actually drives changes in vigilance (Lima and Bednekoff, 1999b).

In their model, Lima and Bednekoff applied the logic of the risk allocation hypothesis to vigilance in groups. The risk allocation hypothesis suggests that animals facing temporal changes in predation risk should allocate more anti-predator effort at times of greater risk. If animals expect to split their time between a small and a larger group, predation risk should vary temporally because individuals in large groups are more protected. Now, if an individual needs to accumulate a fixed amount of resources over the entire time period, how should it allocate anti-predator vigilance in these different groups to maximize fitness? The model showed that individuals should be more vigilant in the riskier situation, namely, when group size is smaller. Without variability in group size over the foraging time horizon, vigilance should be independent of group size.

The implication is that temporal fluctuation in group size can drive the group-size effect on vigilance. I am not aware of any direct test of this hypothesis with respect to anti-predator vigilance. An odd feature of the model is that group size is imposed on foragers for a fixed period of time. What prevents foragers from choosing the group size they like was not specified. In addition, the only source of safety in the model is provided by group size. However, foraging animals can seek shelter in a refuge like a bush or a hole in the ground. When a refuge from predation is available, animals in a large group could feed faster, at the expense of vigilance, to seek shelter rather than stay exposed during the whole period, questioning the prediction that vigilance is independent of group size if group size is constant (Beauchamp and Ruxton, 2011). This model challenges assumptions at the very core of traditional anti-predator vigilance models. Despite the previous caveats, more attention should be allocated to testing its predictions.

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