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Ecology and evolution2013; 3(9); 3073-3082; doi: 10.1002/ece3.694

Local density and group size interacts with age and sex to determine direction and rate of social dispersal in a polygynous mammal.

Abstract: Movement away from an area or social group in response to increasing density (density-dependent dispersal) is known for most species; why it evolves is fundamental to our understanding of ecology and evolution. However, we have yet to fully appreciate how individuals of varying conditions (e.g., age and sex) might differently consider effects of density (quorum) when deciding to disperse or not, and scale dependence in their sense of quorum. We tracked movements of all individuals of a naturalized population of feral horses (Equus ferus caballus; Sable Island National Park Reserve, Nova Scotia, Canada) during a period of rapid population growth (N increased from 375 to 484 horses from 2008 to 2010). Permanent dispersal from breeding groups (bands) was positively density dependent for all age and sex categories with respect to local density (horses/km(2), bounded by the 99th percentile of individual movements [8000 m]), but was negatively and positively density dependent for males and females, respectively, in relation to group (band) size. Dispersal was generally female biased, with the exception of foals which moved with their mothers (no sex effect), and for yearlings and subadults when band sizes were smaller than average, in which case males dispersed at higher rates than females. Dispersal distance was positively related to local density. We conclude that dispersal rate can be both positively and negatively density dependent for feral horses, contingent on the state of individuals and the scale at which quorum with respect to choosing to disperse or not is assessed. Scale effects and interactions of density-dependent and sex- and age-biased dispersal may have both ecological and evolutionary consequences through effects on resource and mate competition.
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Publication Date: 2013-08-01 PubMed ID: 24101995PubMed Central: PMC3790552DOI: 10.1002/ece3.694Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research paper investigates how density-induced movement or dispersal patterns among a population of feral horses are influenced by individual conditions such as age and sex. The study reveals that both males and females display density-dependent dispersal, but their responses differ according to their local group sizes.

Understanding the Research Paper

The research paper aims to understand how patterns of population dispersion among a species (in this case, feral horses) are influenced by variables such as the density of the local population, and individual characteristics like age and sex.

  • Objective: The key goal of the study is to comprehend why density-dependent dispersal evolves among species and how different individuals, based on their age and sex, consider the effects of density (quorum) when deciding whether to disperse or not.
  • Method: The researchers tracked the movements of all members of a feral horse population on the Sable Island National Park Reserve in Nova Scotia, Canada during a period of rapid population growth.

Findings of the Research Paper

The observations and conclusions of the study correspond to the relationship between dispersal, individual conditions, and local group sizes.

  • Density-dependent Dispersal: All members of the horse population, irrespective of their age or sex, showed a propensity to disperse from their breeding groups with increasing local density, but at different rates and in different ways.
  • Varied Responses due to Age and Sex: Dispersal was observed to be generally more common in female horses, with the exception of foals who moved with their mothers, and with yearlings and subadults from smaller bands, where males dispersed at higher rates.
  • Impact of Group Size: In terms of group size, male horses present a negative density-dependent dispersal rate, whereas female horses display a positive density-dependent relationship. This implies that males are more likely to leave as group size increases, while females are more inclined to stay or even join larger groups.
  • Dispersal Distance: The distance covered during dispersal was found to be positively related to local density, indicating that individuals were likely to move further away in areas with a higher density.

Concluding Thoughts

According to the study, dispersal rates can be both positively and negatively density-dependent among feral horses, depending on the state of individuals and the scale at which density is evaluated. These scale effects and the interaction of density-dependent dispersal with sex- and age-biased dispersal could have important ecological and evolutionary implications through their impact on resource competition and mate selection.

Cite This Article

APA
Marjamäki PH, Contasti AL, Coulson TN, McLoughlin PD. (2013). Local density and group size interacts with age and sex to determine direction and rate of social dispersal in a polygynous mammal. Ecol Evol, 3(9), 3073-3082. https://doi.org/10.1002/ece3.694

Publication

Ecology and evolution
ISSN: 2045-7758
NlmUniqueID: 101566408
Country: England
Language: English
Volume: 3
Issue: 9
Pages: 3073-3082

Researcher Affiliations

Marjamäki, Paula H
  • Department of Biological Sciences, Imperial College Silwood Park, Ascot, Berkshire, SL5 7PY, UK.
Contasti, Adrienne L
    Coulson, Tim N
      McLoughlin, Philip D

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        Citations

        This article has been cited 11 times.
        1. Medill SA, Janz DM, McLoughlin PD. Hair Cortisol Concentrations in Feral Horses and the Influence of Physiological and Social Factors.. Animals (Basel) 2023 Jun 27;13(13).
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        2. Colpitts J, McLoughlin PD, Poissant J. Runs of homozygosity in Sable Island feral horses reveal the genomic consequences of inbreeding and divergence from domestic breeds.. BMC Genomics 2022 Jul 12;23(1):501.
          doi: 10.1186/s12864-022-08729-9pubmed: 35820826google scholar: lookup
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        4. Marjamäki PH, Dugdale HL, Dawson DA, McDonald RA, Delahay R, Burke T, Wilson AJ. Individual variation and the source-sink group dynamics of extra-group paternity in a social mammal.. Behav Ecol 2019 Mar-Apr;30(2):301-312.
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