Aggression in the Lizard Anolis acutus

Abstract

The aggressive behavior of adult males and females of the iguanid lizard Anolis acutus was studied in the field. Aggressive encounters were classified as low intensity or high intensity. A. acutus has a high population density, small territories and a single tree has numerous males and females. The unit of observation for each study was a single tree. The observations on a tree included the number of lizards seen every 5 min interval, the number and intensity of encounters, and on trees with marked lizards the position and activity of each lizard. An aggression index was calculated for each population on a tree: the number of encounters per hour divided by the number of lizards sighted per hour X 10. Undisturbed populations demonstrated a normal level of aggression; aggressive encounters increased linearly as the number of lizards observed increased. Encounters doubled with a doubling of the population. The aggression index did not increase with an increase in the population. Males and females demonstrated equivalent levels of aggression and in a given population the aggression of one sex was independent of the other. Removing a lizard from a tree caused an immediate increase in aggression that subsided when the vacated territory was reoccupied. The return of a previously removed lizard also increased aggression. Most aggressive encounters observed were of low intensity, and high intensity encounters were more common in disturbed than in undisturbed populations. The methods used permit a quantitative study of the relationship between territory and aggression.