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The effect of prey density on predators: Conspicuousness and attack success are sensitive to spatial scale

Morrell, Lesley�J.; Ioannou, Christos C.; Ioannou, Christos�C.; Morrell, Lesley J.; Ruxton, Graeme�D.; Ruxton, Graeme D.; Krause, Jens


Lesley�J. Morrell

Christos C. Ioannou

Christos�C. Ioannou

Graeme�D. Ruxton

Graeme D. Ruxton

Jens Krause


In contrast to the numerous studies that have examined the response of predators to prey group size, little is known about how prey density affects prey detection and the accuracy of attacks. We demonstrate that increasing the density of Daphnia magna swarms increases conspicuousness to a natural predator, the three-spined stickleback. Denser areas of groups were more conspicuous, as the fish attacked prey in denser parts of the group than would be expected if they attacked the nearest prey upon entering the feeding chamber. The spatial error of attacks also increased with the density around the target; hence, different stages of predation (searching for vs. successfully attacking prey) seem to select for opposing responses to prey density. However, whereas the effect of density on target selection only occurred using a global measure of density (average interindividual distance), the effect on attack error was only significant using a local measure of density (Voronoi polygon area). We believe this effect of spatial scale reflects the reduction in the number of prey in the visual field of the predator as an attack progresses, providing a perceptual basis for the importance of spatial scale in density-dependent processes.


Ioannou, C. C., Morrell, L. J., Ruxton, G. D., & Krause, J. (2009). The effect of prey density on predators: Conspicuousness and attack success are sensitive to spatial scale. The American naturalist, 173(4), 499-506.

Journal Article Type Article
Acceptance Date Sep 24, 2008
Online Publication Date Feb 20, 2009
Publication Date Apr 1, 2009
Print ISSN 0003-0147
Electronic ISSN 1537-5323
Publisher University of Chicago Press
Peer Reviewed Peer Reviewed
Volume 173
Issue 4
Pages 499-506
Keywords Ecology, Evolution, Behavior and Systematics
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