Exploring mixed-species grouping effects through antipredator mechanisms

Abstract

Predation is an important selective force for prey organisms, which have also developed different antipredator adaptions. Individuals of many animal species live in the group, which is generally believed to offer prey benefits from reduced predation risk and/or increased foraging efficiency. Different antipredator mechanisms of grouping prey have been well-developed theoretically and studied extensively for single species groups as compared to mixed-species groups. Yet, there has been a lack of understanding of how some antipredator mechanisms would be affected when applied to a mixed-species group due to additional effect of the within-group heterogeneity of prey.

This thesis explored the consequence of mixed-species grouping on the risk related to predation, with the intention to expand current understanding of the antipredator mechanisms for heterogeneous prey groups of multi-species or more broadly multi-phenotypes. Using artificial prey to simulate prey groups, the first several studies empirically examined how the prey group as a whole—varied in prey composition, group size, within-group position and compactness—would affect the ease of detection by free-living animals and/or ‘human predators’. The last study investigated grouping effects, especially the effect of the nearest associated species on individual’s vigilance and foraging in the aggregation of avian species feeding on a feeder.

Significant effects of group patterns on the detection risk of artificial prey groups were mostly found in experiments with ‘human predators’ rather than animal predators. Despite some contradictory findings between different predator-prey systems, these studies generally lent support to the idea consistent with the ‘giveaway cue’ hypothesis, where polymorphic population with prey of conspicuous morph may attract predations’ attention; and showed that the inclusion of conspicuous prey in mixed-species group would increase the detection risk of prey compared to some single species groups. Together, all the studies demonstrated the influence of mixed-species association on prey detection and/or predation risk.