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Thesis open access


Dominance relationships are an important aspect of the social organization of many species. Male dominance often results in successful territory defense and/or access to potential mates, and thus is a central component in establishing social rank. In this study, I used mathematical models to consider social interactions of the green anole lizard (Anolis carolinensis) in both territorial and hierarchical contexts. I then identified the behavioral and morphological traits associated with dominance in this species.

I first analyzed a series of ranking algorithms to evaluate their effectiveness as a novel approach to quantifying animal social status. I found that all eight systems considered in this analysis successfully reflected dominance relationships in the green anole; however, no one system consistently predicted ranks using the measured traits. Therefore ranking systems are a viable method of analyzing social hierarchies in anoles, yet multiple systems are required to effectively model these dominance relationships.

I then performed three empirical studies using the eight ranking systems from the previous analysis. In the first study, I performed a tournament of arena trials using pairs of 18 male lizards to identify the traits most closely related to male social status in a dominance hierarchy. These arena trials stimulated aggressive interactions, often resulting in a clearly dominant male. I used the resulting win/loss/tie information in the ranking algorithms to rank the individuals. My results showed that behavioral displays and relative head length were the most predictive of rank in the majority of ranking systems. In my next study, I measured morphological traits, aggressive behavior, territory size, and female overlap (a proxy of territory quality) in 24 green anoles in Palmetto State Park, Gonzales, Texas, to determine how these traits were related to territory size and/or quality in a natural population. Results from this study indicated that body size and head length were important predictors of territory size, and head length was the only significant predictor of territory quality. Finally, I sought to validate my results by directly comparing male rank to territory size. In two replicate studies with 10 male lizards each, I first used a series of arena trials to determine individuals’ ranks. I then placed the 10 males into an enclosure with 10 females and measured the sizes of male territories over one week. Although I hypothesized that higher ranked males would have larger territories, I found no correlation between rank and territory size.

Overall, these results suggest that head length is an important component of all aspects of dominance (rank, territory size, and territory quality) in the green anole. Head size is closely related to bite force in anoles and is an honest predictor of fighting ability in this species. This study demonstrates that combining animal-based studies with mathematical models is an effective method of analyzing vertebrate social dynamics.

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