Resource distribution and social structure in harem-forming Old World fruit bats: variations on a polygynous theme

The prediction that the spatial dispersion of resources that are important to females should dictate female dispersion and male mating tactics has not been previously tested in harem-forming bats. We investigated the relation between the estimated spatial distribution of available roosts, female group size, male roost fidelity and the strength of social associations in two species of harem-forming fruit bats in the genus Cynopterus. We evaluated the daily movements of individuals and groups among roosts using radiotelemetry and roost censuses at two sites in northern peninsular Malaysia. We found a high correspondence between the distribution of roost sites, female group size and male behaviour, supporting the prediction that clumped resources would promote female aggregation and high roost fidelity in males. However, there were significant interspecific differences in the strength of male–female associations, which suggested that, where roosts are abundant and similar in quality, regardless of their spatial distribution, the potential for males to monopolize mates depends on whether females move among roosts with, or independently of, males. We propose that interspecific differences in female behaviour may be related to the costs of moving between clumped versus randomly dispersed males.