title: Overestimations of food abundance: predator responses to prey aggregation.
abstract: Understanding and predicting the consequences of trophic interactions for community processes requires knowledge of the role of food availability, which is often wrongly conflated with prey abundance. For prey animals in groups, this is not fully understood. Previous work has shown that oystercatchers more frequently attack solitary rather than aggregated limpets and are more successful in predation attempts on singletons. It has also been demonstrated that an attack on one limpet in a group alerts the entire group, all of which then clamp down and become unavailable. I show that Eurasian Oystercatchers (Haematopus ostralegus L.) attack only one limpet in a group and then move on to attack another individual limpet, and I also demonstrate that the distance they move is greater than the distance at which groups of limpets have been known to detect attacks. Thus in the oystercatcher-limpet predator-prey system on rocky shores, groups of limpets are actually one prey item independently of the number of limpets in the group. This has implications for assessment of food supply for avian predators on rocky shores, with consequences for our understanding of previously documented trophic cascades.
authors.affiliation: Marine Biology and Ecology Research Centre, School of Biological Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, United Kingdom. ross.coleman@bio.usyd.edu.au
authors.forename: Ross A
authors.initials: RA
authors.lastname: Coleman
mesh_terms: D000818:Animals; D001717:Birds / Q000502:physiology*; D019587:Dietary Supplements; D020387:Food Chain; D008954:Models, Biological; D008974:Mollusca / Q000502:physiology*; D011156:Population Density; D011235:Predatory Behavior / Q000502:physiology*