Indirect and Direct Effects of Competitor Presence on Behavior of Introduced Anoles in Hawai‘i

Abstract

The intensity and frequency of aggressive behaviors are often used as evidence for interference competition. Much like the non-consumptive effects of predators on prey, competitor presence and/or costly aggressive interactions could have indirect effects on competitor behavior. Although phenomena consistent with competition between Anolis carolinensis and Anolis sagrei have been well documented, the mechanism driving the interaction is largely unknown and little work has examined the direct and indirect effects of competitor presence when these species co-occur. Using focal animal sampling, we compared time budgets of each species when housed in experimental mesocosms containing either one or both species. Interspecific aggression was not observed, suggesting that aggressive interference is not a mechanism driving competition. However, individuals of both species when in the presence of their competitor behaved differently compared to individuals in the absence of their competitor. Alterations in time spent engaged particularly in foraging and display behaviors could explain changes in population sizes and habitat use when these species co-occur and also suggests that multiple mechanisms, as opposed to just interference or exploitation, may be driving competition between A. sagrei and A. carolinensis.