UC Davis

While it is well recognized that animals use social information (i.e., information gleanedfrom conspecifics) to guide behavior, little attention has been given to the role of social information use in shaping responses to novel situations, such as those introduced by rapid environmental change. The three chapters of my dissertation focus on how evolved decision making strategies that use social information can become maladaptive in changing environments. I examined how something as simple and fluctuating as group size and composition can alter individual behaviors of fish, including the common evolutionary trap of eating plastic. The “group size effect” is a classic phenomenon found across taxa, in which animals in larger groups show less vigilance behavior and more foraging behaviors. I looked at whether this common effect could carry over into novel situations by presenting novel foods with varying fitness benefits and costs to fish shoals of different sizes. I studied these questions in Western mosquitofish (Gambusia affinis), an ideal system to test how variation in group size might influence behaviors because they naturally live within fission-fusion societies, and thus experience constant changes in social aggregations. By studying individual foraging behaviors toward both known and novel food items, I was able to directly compare how individuals changed in their responses across the different foraging situations. The experiments provide evidence that group dynamics can influence the severity of a socially-mediated evolutionary trap and that, regardless of the number of members, group identity can have a strong effect on individual behavior. Furthermore, while social roles vary within a group based on group size, within-group variation in susceptibility to an evolutionary trap can be associated with social position.