Oecologia

, Volume 149, Issue 3, pp 543–552

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

  • Alvaro Soutullo
  • Rubén Limiñana
  • Vicente Urios
  • Martín Surroca
  • Jennifer A. Gill
Behavioural Ecology

DOI: 10.1007/s00442-006-0465-5

Cite this article as:
Soutullo, A., Limiñana, R., Urios, V. et al. Oecologia (2006) 149: 543. doi:10.1007/s00442-006-0465-5

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 by 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 population increased exponentially between 1981 and 2001, but stabilised 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.

Keywords

Allee effectBuffer effectDensity dependenceIdeal despotic distributionIdeal free distribution

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Alvaro Soutullo
    • 1
  • Rubén Limiñana
    • 1
  • Vicente Urios
    • 1
  • Martín Surroca
    • 2
  • Jennifer A. Gill
    • 3
  1. 1.Estación Biológica Terra Natura (CIBIO-Fundación Terra Natura) Universidad de AlicanteAlicanteSpain
  2. 2.Centro de recuperación de Fauna “Forn del Vidre”Generalitat ValencianaCastellonSpain
  3. 3.School of Biological SciencesUniversity of East AngliaNorwichUK