Published in Journal of Herpetology, Vol. 43 No. 3 (September 2009) at


Agonistic behavior is a common feature of larval amphibians inhabiting temporary ponds. Given the temporally staggered sequence of hatching by pond-breeding amphibians, ontogenetic patterns of aggression can influence coexistence if larvae of certain species or ages are subject to increased aggression. To determine whether aggression changes through larval ontogeny, we observed agonistic behavior of Ambystoma opacum, Ambystoma tigrinum, and Ambystoma maculatum at four stages of development spanning the larval period. We tracked aggression rates among individual larvae to determine whether previous success, in the form of increased aggression, facilitated success in subsequent contests. All species exhibited distinct ontogenetic patterns of aggression, with the highest and lowest rates of aggression exhibited during rear leg development and metamorphosis, respectively. Species-specific aggression rates were observed, with A. tigrinum consistently displaying the highest levels of aggression. Winner or loser effects were not evident, because increased aggression early in the larval period did not result in increased aggression throughout ontogeny. We hypothesize that the observed patterns of behavior may represent a baseline level of aggression upon which other biotic and abiotic factors act in mediating coexistence among larval amphibians.