Document Detail

Food-limitation in a generalist predator.
MedLine Citation:
PMID:  16846915     Owner:  NLM     Status:  MEDLINE    
Investigating food-limitation in generalist predators is difficult, because they can switch to alternative prey, when one of their staple prey becomes scarce. Apart from data on the dynamics of the predator population, a robust study requires: (i) a documentation of the predator's entire prey base; and (ii) an experimental or natural situation, where profitable dietary shifts are impossible, because several preferred prey species decline simultaneously. Here, we provide a detailed description of how food-supply has limited a generalist avian top predator, the northern goshawk Accipiter gentilis. In our study area, populations of several principal goshawk prey species crashed simultaneously during 1975-2000, whereas other extrinsic factors remained essentially unchanged. The breeding and non-breeding segments of the local goshawk population declined markedly, associated with a significant increase in nest failures. Brood size of successful pairs remained unaffected by changes in prey availability. Breeding recruitment ceased at a time when potential replacement birds ('floaters') were still present, providing a rare empirical demonstration of an 'acceptance threshold' in raptor territory choice. To investigate how goshawk diet changed in response to varying food-supplies, we make novel use of an analytical tool from biodiversity research-'abundance-biomass-comparison curves' (ABC curves). With increasing levels of food-stress, the dominance of principal prey species in the diet decreased, and the number of small-bodied prey species increased, as did intra-guild predation. Our finding that breeder and non-breeder segments declined in concert is unexpected. Our results carry the management implication that, in food-limited raptor populations, externally induced breeder mortality can rapidly depress population size, as losses are no longer buffered when floaters reject breeding opportunities.
Christian Rutz; Rob G Bijlsma
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Proceedings. Biological sciences / The Royal Society     Volume:  273     ISSN:  0962-8452     ISO Abbreviation:  Proc. Biol. Sci.     Publication Date:  2006 Aug 
Date Detail:
Created Date:  2006-07-18     Completed Date:  2006-09-18     Revised Date:  2013-06-07    
Medline Journal Info:
Nlm Unique ID:  101245157     Medline TA:  Proc Biol Sci     Country:  England    
Other Details:
Languages:  eng     Pagination:  2069-76     Citation Subset:  IM    
Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
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MeSH Terms
Columbidae / physiology
Falconiformes / physiology*
Feeding Behavior*
Food Chain
Population Density
Population Dynamics
Predatory Behavior*

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