Aggression and exploitation as mechanisms of competition in larval salamanders

We investigated the mechanisms of competition between two species of larval salamanders, Ambystoma talpoideum and Ambystoma maculatum. A laboratory experiment revealed that A. maculatum suffered higher mortality during early periods of larval growth when raised with its congener, A. talpoideum, than it did when combined with conspecifics. Ambystoma maculatum had no effect on the survivorship of A. talpoideum. However, A. maculatum inhibited the growth of A. talpoideum as well as that of conspecifics. This inhibition of growth may be evidence of exploitative competition for food. In a second experiment, A. talpoideum was more aggressive (a form of interference competition) than A. maculatum to both conspecific and heterospecific larvae. These results suggest that coexistence between these two species of larval salamanders results from a trade-off between exploitative and aggressive superiorities.