WHAT DETERMINES FITNESS WHEN DISPERSAL IS LIMITED

Simple evolutionary models typically assume a homogeneous environment in which all individuals have equal access to resources. However, when dispersal is limited this assumption is unlikely to correspond to rea lity. Instead, the offspring of relatively fecund parents can be expec ted to find that resources are scarce because of competition from thei r relatively large number of siblings. We show that these factors lead to selection for decreased variation in the number of offspring produ ced. We investigate the relationship between fitness and variation in fertility for a variety of different circumstances. Our results indica te that, in some cases, selection far reduced variation in fertility c an be very substantial.