Causes and consequences of sociality: Time allocation, individuality, and the evolution of group size in mammals

Animals vary dramatically in their sociality; social groups differ in size, cohesiveness, and complexity. Why this is so is one of the greatest mysteries in behavioral biology. Researchers have proposed a variety of ecological and life history factors that lead to, or arise from, these differences in sociality. In my dissertation, I focus on two comparatively under-explored factors: time allocation and individuality. How animals allocate their limited daily time to different activities is influenced by sociality in complex ways. Time budgeting requirements can thus permit or constrain evolutionary changes in social group size. Similarly, social behavior is influenced by animals' ability to discriminate other individuals; levels of individuality may thus permit or constrain changes in social group size. I address these questions in a comparative context, looking for broad patterns across multiple species. Using 50 species of diurnal primates, I tested eight hypotheses relating time allocation to social group size. I found that resting time was negatively related to group size. This suggests daily time is an important resource whose use is affected by sociality and that resting time restrictions may constrain social group size. For individuality, I used acoustic analysis and information theoretic measures to quantify vocal individuality in alarm calls. I used computer models to uncover benefits of individuality and found that receivers increase their fitness by attending to the reliability of individual signallers. I furthermore described how individuality metrics can aid ecological research and conservation. Testing across 8 species of ground-dwelling sciurid rodents, I found a strong positive relationship between individuality and social group size, suggesting that large groups generate selective pressure for increased individuality and that increased individuality may permit the formation of larger social groups. Results indicate that two previously understudied factors, time allocation and individuality, are important in the evolution of sociality. These factors warrant inclusion in sociality models and are key to our understanding of how and why sociality evolves.