Behavioral Ecology Advance Access published online on December 3, 2008
Behavioral Ecology, doi:10.1093/beheco/arn149
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Behavioral changes associated with a population density decline in the facultatively social red fox
School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
Address correspondence to G. Iossa. P.J. Baker is now at the School of Biological Sciences, University of Reading, Whiteknights, Reading, Berkshire RG6 6AS, UK. E-mail: g.iossa{at}bristol.ac.uk.
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Abstract |
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Understanding the causal mechanisms promoting group formation in carnivores has been widely investigated, particularly how fitness components affect group formation. Population density may affect the relative benefits of natal philopatry versus dispersal. Density effects on individual behavioral strategies have previously been studied through comparisons of different populations, where differences could be confounded by between-site effects. We used a single population of red foxes (Vulpes vulpes) in the city of Bristol, UK, that underwent a natural perturbation in density to compare key changes in 1) group structure, 2) within-group relatedness, 3) mating system, 4) dispersal, and 5) dominance attainment. At high densities (19.6–27.6 adults km–2), group sex ratios were equal and included related and unrelated individuals. At low densities (4.0–5.5 adults km–2), groups became female biased and were structured around philopatric females. However, levels of within-group relatedness were unchanged. The genetic mating patterns changed with no instances of multiple-paternity litters and a decline in the frequency of extrapair litters of cubs from 
77% to 38%. However, the number of genetically monogynous groups did not differ between periods. Dispersal was male biased at both high and low densities. At high density, most dominant males in the study groups appeared to have gained dominance after dispersing, but natal philopatry was an equally successful strategy at low density; conversely, most dominant females were philopatric individuals at both high and low densities. These results illustrate how density may alter behavioral strategies such as mating patterns and how this, in turn, alters group structure in a single population.
Key words: carnivores, dispersal, dominance attainment, extrapair fertilizations, multiple paternity, sociality.
* These authors contributed equally to this work.
Received 8 May 2008; revised 27 October 2008; accepted 30 October 2008.