Testing the independent effects of population and shelter density on behavioural and corticosterone responses of tree skinks
Peter Lancaster A , Tim S. Jessop A B C and Devi Stuart-Fox A
+ Author Affiliations
- Author Affiliations
A Department of Zoology, University of Melbourne, Vic. 3010, Australia.
B Department of Wildlife Conservation and Science, Zoos Victoria, Vic. 3052, Australia.
C Corresponding author. Email: tjessop@unimelb.edu.au
Australian Journal of Zoology 58(5) 295-302 https://doi.org/10.1071/ZO10056
Submitted: 26 August 2010 Accepted: 22 November 2010 Published: 27 January 2011
Abstract
In animals, social organisation and behaviour can respond to variation in key ecological factors including population and resource density. As these two factors covary, their relative importance is difficult to estimate using field studies. Consequently, we conducted two manipulative experiments varying levels of either population or shelter density to separate their effects on solitary, affiliative and agonistic behaviour and physiology in the social tree skink, Egernia striolata. We used focal observations and plasma concentrations of the hormone corticosterone to measure behavioural and physiological responses to these manipulations. Aggressive behaviours occurred more frequently at high skink density, with males at high density exhibiting social stress, as indicated by increased levels of corticosterone. Skinks at low densities showed greater affiliative behaviour, spending more time basking as pairs. Changes in shelter density influenced exploratory behaviours, with males at low shelter densities exploring enclosures more than those at high shelter densities. Skinks sheltered as pairs more frequently at low shelter density, even after taking into account differences in frequency of pair sheltering expected by chance alone, suggesting that low shelter availability promotes pair behaviour. Corticosterone levels increased over time at low shelter density, which may have been a result of thermal stress coupled with a lack of microclimate variation in comparison to high shelter density. These results suggest that population and resource density are key factors that can independently influence social behaviour and endocrinology, and consequently social organisation, in different ways.
Additional keywords: resource density, lizard, Egernia striolata, affiliative behaviour, aggressive behaviour.
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