Abstract
Empirical studies of the determinants of contests have been attempting to unravel the complexity of animal contest behaviour for decades. This complexity requires that experiments incorporate multiple determinants into studies to tease apart their relative effects. In this study we examined the complex contest behaviour of the tawny dragon (Ctenophorus decresii), a territorial agamid lizard, with the specific aim of defining the factors that determine contest outcome. We manipulated the relative size and residency status of lizards in contests to weight their importance in determining contest outcome. We found that size, residency and initiating a fight were all important in determining outcomes of fights. We also tested whether residency or size was important in predicting the status of lizard that initiated a fight. We found that residency was the most important factor in predicting fight initiation. We discuss the effects of size and residency status in context of previous studies on contests in tawny dragons and other animals. Our study provides manipulative behavioural data in support of the overriding effects of residency on initiation fights and winning them.
Highlights
Identifying factors that influence the outcomes of costly contests is a classical field in evolutionary biology [1,2,3]
To investigate the determinants of contest outcome and initiation in the tawny dragon, Ctenophorus decresii we focused on the importance of size and residency status and how these interact to determine contest outcome and initiation
Residency status, and initiating a contest were all significant predictors of winning a contest
Summary
Identifying factors that influence the outcomes of costly contests is a classical field in evolutionary biology [1,2,3]. Asymmetries between males in body size and residency status are associated with an individual’s likelihood of winning fights and as such are deemed determinants of contest success [4]. Other factors can override the effects of body size, such as prior contest experience [11] or being a territory holder (resident) [6,12,13,14]. Several hypotheses explain why this is so: (1) better males are intrinsically more likely to be territory holders; (2) residency status is a conventional cue by which to settle contests (‘bourgeois strategy’) [15,16]; (3) residency leads to changes in the intrinsic quality of the resident [14,17]; and/or (4) residents place greater value in their own territory than opponents place in the resident’s territory because of their experience with it [13,18]
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