Causes and Consequences of Fission-Fusion Dynamics in Female Northern Long-Eared Bats, Myotis septentrionalis

Abstract

Individual costs and benefits of living in groups vary with group size, stability, and composition. Investigations of these features of group living have lead to the recognition of a variety of social structures. Although many studies have examined social structure in animals with long-term, stable groups, little is known about groups with highly variable group size and composition, such as fission-fusion dynamics. In this thesis I examined the causes and consequences of fission-fusion dynamics by exploring the socioecology of female northern long-eared bats, Myotis septentrionalis. Like many temperate bats, female northern long-eared bats show natal philopatry to summer areas. During this time, they live in groups with fission-fusion dynamics as individuals move among a network of roosts and roost-groups. To examine the causes of fission-fusion dynamics, I examined why females switch roosts. To address the consequences of these dynamics, I asked whether females could form stable relationships, and what factors might explain these relationships. I was able to identify the possible causes and consequences of fission-fusion dynamics that had not yet been explored in bats. I demonstrated that fission-fusion dynamics may be explained, at least in part, by changes in ambient conditions that prompt frequent roost-switching. Despite the highly dynamic nature of these groups, females formed long-term social relationships that were based in part on age and genetic relatedness. These findings have potential consequences for the evolution of social behaviour within groups, such as cooperation and nepotism. My work also raised several questions that require further examination to fully understand the evolution of fission-fusion dynamics. For example, the question remains whether species or sympatric groups of conspecifics with different degrees of roost-switching show the same social structure. By answering these questions, we can gain a better understanding of the causes and consequences of fission-fusion dynamics across species of bats. Once this is achieved, we can then look for parallels with other taxa to answer questions about the evolution of these dynamic systems.