Prospective Resource Defense in a Territorial Species

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Abstract
Prospective resource defense, or present defense of resources which will be required in the future, was tested for territorial juvenile lizards (Anolis aeneus). In this species, juveniles 20-30 mm in size defend territories in clearings; the number of future days that a juvenile will require a territory in the clearing is inversely related to its size. All juveniles 20-30 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 sized-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 flot around clearings; large juveniles cannot. Because floaters outcomplete 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 A. 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 is explained by changes in immediate and prospective resource values.