Personality in agama lizards and chacma baboons : methodological considerations across taxa




Carter, Alecia Jillian

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A view long held by evolutionary biologists is that individuals within a population should modify their behaviour to suit the current physical and social environment. However, recent empirical studies challenge this view, suggesting that persistent between-individual differences in behaviour - animal personalities - are not 'noise', but can be adaptive. Despite a surge of recent interest in the study of animal personalities, the field is proving to be fraught with conceptual and methodological difficulties. I investigated a number of fundamental problems facing the field of animal personality. In the first part of the thesis, I focus on methodological considerations, which I review in detail, suggesting tools that can be used to overcome current difficulties. Subsequently, I describe a behavioural syndrome in wild Namibian rock agamas Agama planiceps that shows a link between risk-taking behaviour and three other variables: time spent conspicuous, home range size and predation risk. This suggests different costs and benefits for boldness in this species. I then demonstrate that bolder agamas were more trappable than shyer agamas. Using a simulation model, I show that sampling bias may lead to underestimation of the effect sizes of correlations between behavioural traits. These results have important implications for studies where individuals are caught in the wild and taken into captivity. Next, I tested assumptions about commonly used personality assays by measuring boldness in wild baboons Papio ursinus in three ways: using subjective ratings by experienced observers, individual responses to a novel food, and responses to a threat. I show that subjective ratings and novel food responses were correlated but that responses to a novel food and a threat did not correlate. My findings suggest that two commonly employed assays of boldness (responses to novel objects and a threatening stimulus) may not measure the same trait, which may have significant implications for animal personality research. In the second part of my thesis, I address conceptual problems of animal personality theory. I investigated whether Namibian rock agamas were constrained by personality types or showed behavioural plasticity when their environmental conditions changed dramatically between the dry and rainy seasons. Behaviour was differentially affected by variation among individuals, variation in the environment and the interaction between the individual and environment suggesting that the relevance of the behaviour to the change in season was important. Next, I investigated social foraging decisions in baboons. I found no evidence that personality affected producer-scrounger decisions when information was reliable, but that personality was important when information was unreliable. In both agamas and baboons, I suggest that where there are reliable environmental cues, individual plasticity will be favoured over consistency in the relevant behaviours, challenging the current conceptualization of animal personality. Overall, my research suggests that animal personality research is currently facing methodological and conceptual obstacles that may hinder its continued progress. I recommend the use of multiple assays for measuring personality traits, and encourage more studies of free-living populations. I also urge that more consideration be given to interpreting the outcome of empirical tests of the subject. -- provided by Candidate.






Thesis (PhD)

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