The Effect of Contender Pressure on Territory Size and Overlap in Seasonally Territorial Species

The current field experiment tests whether contender pressure (the number of individuals competing for territories) affects the territory sizes and territory overlap of a seasonally territorial species. Different numbers of Anolis aeneus juvenile lizards were simultaneously introduced to patches of high-quality habitat in the field, and various methods were used to control for any possible temporal variation in patch quality. Net territory sizes (reflecting both territory size and territory overlap) were consistently smaller when contender numbers were high than when they were low, suggesting that the spacing patterns of A. aeneus juveniles may be affected by contender pressure, independently of variation in habitat quality. In this and other species, contender pressure in a particular patch of habitat may be partly to largely independent of the resource levels in that patch. First, a strong positive relationship between contender pressure and patch quality assumes that potential settlers can accurately assess resources before settling, and this may be difficult or impossible for some species. Second, the numbers of potential settlers arriving at a patch may be determined by selective pressures that are spatially or temporally disjunct from those operating in the territorial habitat. Finally, spatial or temporal variation in resource levels may result in independence or even a negative relationship between patch quality and contender pressure. Hence, contender pressure may affect spacing patterns in a variety of species besides A. aeneus lizards.