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Research article - Peer-reviewed, 2015

Predator-dependent functional response in wolves: from food limitation to surplus killing

Zimmermann B, Sand H, Wabakken P, Liberg O, Andreassen H

Abstract

The functional response of a predator describes the change in per capita kill rate to changes in prey density. This response can be influenced by predator densities, giving a predator-dependent functional response. In social carnivores which defend a territory, kill rates also depend on the individual energetic requirements of group members and their contribution to the kill rate. This study aims to provide empirical data for the functional response of wolves Canis lupus to the highly managed moose Alces alces population in Scandinavia. We explored prey and predator dependence, and how the functional response relates to the energetic requirements of wolf packs. Winter kill rates of GPS-collared wolves and densities of cervids were estimated for a total of 22 study periods in 15 wolf territories. The adult wolves were identified as the individuals responsible for providing kills to the wolf pack, while pups could be described as inept hunters. The predator-dependent, asymptotic functional response models (i.e. Hassell-Varley type II and Crowley-Martin) performed best among a set of 23 competing linear, asymptotic and sigmoid models. Small wolf packs acquired >3 times as much moose biomass as required to sustain their field metabolic rate (FMR), even at relatively low moose abundances. Large packs (6-9 wolves) acquired less biomass than required in territories with low moose abundance. We suggest the surplus killing by small packs is a result of an optimal foraging strategy to consume only the most nutritious parts of easy accessible prey while avoiding the risk of being detected by humans. Food limitation may have a stabilizing effect on pack size in wolves, as supported by the observed negative relationship between body weight of pups and pack size.

Keywords

Canis lupus; faecal pellet group count; hunting success; kill-handling time; moose; numerical response; optimal foraging; predation; scavenging; social organization

Published in

Journal of Animal Ecology
2015, volume: 84, number: 1, pages: 102-112

Authors' information

Zimmermann, Barbara
Hedmark University College
Swedish University of Agricultural Sciences, Department of Ecology
Wabakken, Petter
Hedmark University College
Swedish University of Agricultural Sciences, Department of Ecology
Andreassen, Harry Peter
Hedmark University College

UKÄ Subject classification

Ecology
Zoology

Publication Identifiers

DOI: https://doi.org/10.1111/1365-2656.12280

URI (permanent link to this page)

https://res.slu.se/id/publ/64948