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Mixed-phenotype grouping: the interaction between oddity and crypsis

Rodgers, Gwendolen M.; Kimbell, Helen; Morrell, Lesley J.

Authors

Gwendolen M. Rodgers

Helen Kimbell

Abstract

Aggregations of different-looking animals are frequently seen in nature, despite well-documented selection pressures on individuals to maintain phenotypically homogenous groups. Two well-known theories, the ‘confusion effect’ (reduced ability of a predator to accurately target an individual in a group) and the ‘oddity effect’ (preferential targeting of phenotypically distinct, ‘odd’, individuals) act together to predict the evolution of behaviours in prey that lead to groups of animals that are homogeneous in appearance. In contrast, a recently proposed mechanism suggests that mixed groups could be maintained if one species in a mixed group is more conspicuous against the habitat than the other, as confusion effects generated by the conspicuous species impede predator targeting of the cryptic species; thus, cryptic species benefit from association with conspicuous ones. We test these contrasting predictions from the perspective of both predators and prey, and show that cryptic individual Daphnia are at reduced risk of predation from three-spine sticklebacks Gasterosteus aculeatus when in mixed-phenotype groups, a risk that is reduced further as the number of conspicuous individuals increases, supporting the hypothesis for the evolution of mixed groups. In contrast, while the preference for associating with colour-matched conspecifics by mollies (Poecilia sphenops) was reduced when they were cryptic, we found no evidence for active association with conspicuous conspecifics. We conclude that prey animals must balance the relative risks of oddity and conspicuousness in their social decisions, and that this could potentially lead to the evolution of mixed-phenotype grouping as a response to predation risk alone.

Journal Article Type Article
Publication Date 2013-05
Journal Oecologia
Print ISSN 0029-8549
Electronic ISSN 1432-1939
Publisher BMC
Peer Reviewed Peer Reviewed
Volume 172
Issue 1
Pages 59-68
DOI https://doi.org/10.1007/s00442-012-2473-y
Keywords Mixed-species group, Inter-specific grouping, Oddity effect, Confusion effect, Predation
Publisher URL http://link.springer.com/article/10.1007%2Fs00442-012-2473-y
Additional Information Author's accepted manuscript of article published in: Oecologia, 2013, v.172, issue 1. The final publication is available at Springer via http://dx.doi.org/10.1007/s00442-012-2473-y

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