Defense of mates: a territory departure rule for male tree lizards following sex-ratio manipulation.

Male tree lizards (Urosaurus ornatus) abandon their territories following the removal of potential mates. Departure time averages 25 days but varies from 1 to 7 weeks. We show that most of the variation (r 2=0.78) in departure of males can be accounted for by the number of females removed from male territories and adjacent trees. Males occupying higher quality territories (more potential mates) have short departure times, whereas males on poorer territories (fewer fameles) stay longer after female removal. We hypothesize that the inverse relationship between male departure time and the number of females removed from their territories is a consequence of the male's previous expectation of envountering prospective mates. In addition, experimental introduction of non-resident males into the territories of resident males revealed the inability of intruder males to become established on occupied territories.