Abstracts (first author)
Group formation and individual mortality
In some species, organisms perform key activities in groups. This is the case, for example, when nesting or foraging is communal. The evolutionary advantage of this sort of social behaviour is that group members gain access to vital resources in an amount greater than that accessible through individual effort. In this paper, we explore the relationship between group formation and individual mortality in social species. We make two realistic assumptions: (i) there is a time lag between group formation and the moment in which group members enjoy the result of group activities (i.e. laborious construction of the communal nest, human agriculture); (ii) one or more group members may die during this time interval, and remaining members benefit from this event (i.e. the result of group activities is divided among fewer individuals). Two different situations are considered. First, mortality is independent of age, initially. We examine whether changes in individual mortality may have an impact on fitness when grouping is random. Second, mortality increases with age; i.e. ageing. In this situation, the strategy of choosing older individuals as group mates is selectively superior to random grouping. However, selection on “go-for-the-old” appears to be frequency dependent. Finally, we discuss the potential advantages of “segregate-by-age”, a behaviour that has been observed in some species.