Prospective Resource Defense in a Territorial Species

Abstract

Prospective resource defense, or present defense of resources which will be required in the future, has been tested for territorial juvenile lizards (Anolis aeneus). In this species, juveniles 20 to 30 mm in size defend territories in clearings, and the number of future days that a juvenile will require a territory in the clearing is inversely related to its size. All juveniles 20 to 30 mm in size use the same types of territories, and the immediate (daily) value of the territory is either positively related to juvenile size or is size-independent. Food is superabundant for all juveniles, and all juveniles require a predator-safe homesite. There is no indication that predation on juveniles is size-dependent. Small juveniles have options other than territoriality available to them; small juveniles can float around clearings whereas large juveniles cannot. Because floaters outcompete transients for homesites, small juveniles would be more apt to gain a replacement territory than would large juveniles. Juveniles on matched, semiartificial territories in the field were presented with same-sized tethered intruders. There was a strong negative relationship between size and aggression toward intruders, supporting the prospective resource hypothesis. Additional support for prospective resource defense in Anolis aeneus comes from adult males and females 44-50 mm in size. Both sexes require comparable resources, but adult females are much more sedentary than young males, and the former are much more aggressive than the latter. In this species, ontogenetic and sexual changes in aggression toward territorial intruders can best be explained by changes in both immediate and prospective resource values.