Density-dependent regulation of population size in colonial breeders : Allee and buffer effects in the migratory Montagu's Harrier

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Title: Density-dependent regulation of population size in colonial breeders : Allee and buffer effects in the migratory Montagu's Harrier
Authors: Limiñana, Rubén | Soutullo, Alvaro | Urios, Vicente | Surroca Royo, Martín | Gill, Jennifer A.
Research Group/s: Zoología de Vertebrados
Keywords: Aguilucho cenizo | Población | Migración
Knowledge Area: Zoología
Date Created: 2006
Issue Date: 2-Jul-2007
Abstract: Expanding populations offer an opportunity to uncover the processes driving spatial variation in distribution and abundance. Individual settlement decisions will be influenced by the availability and relative quality of patches, and how these respond to changes in conspecific density. For example, conspecific presence can alter patch suitability through reductions in resource availability or territorial exclusion, leading to buffer effect patterns of disproportionate population expansion into poorer quality areas. However, conspecific presence can also enhance patch suitability through Allee effect processes such as transmission of information about resources or improved predator detection and deterrence. Here we explore the factors underlying the settlement pattern of a growing population of Montagu’s Harriers (Circus pygargus) in Spain. The harrier population increased exponentially between 1981 and 2001 but stabilized between 2001 and 2004. This population increase occurred alongside a remarkable spatial expansion, with novel site use occurring prior to maximum densities in occupied sites being reached. However, no temporal trends in fecundity were observed and, within sites, average fecundity did not decline with increasing density. Across the population, variance in productivity did increase with population size, suggesting a complex pattern of density-dependent costs and benefits. We suggest that both Allee and buffer effects are operating in this system, with the benefits of conspecific presence counteracting density-dependent declines in resource availability or quality.
URI: http://hdl.handle.net/10045/883
Language: eng
Type: Other
Peer Review: si
Appears in Collections:INV - ZV - Pósters
INV - CYT - Otros Trabajos de Investigación

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