How Blue-Spotted and Small-Mouthed Salamander Larvae Coexist With Their Unisexual Counterparts

Species of pond-breeding salamanders in the Great Lakes region often coexist with unisexual (all-female) populations that compete with larvae and are sexual parasites on adult males. We evaluated the effects of interactions with the larvae from unisexual salamander (Ambystoma laterale-complex) populations on blue-spotted (A. laterale) and small-mouthed salamander (A. texanum) larvae. We coupled observations in natural ponds with mesocosm and laboratory approaches to investigate the roles of competition, predation, microhabitat partitioning, and behavior on the coexistence of these populations. Unisexual salamander larvae increased mortality, reduced growth, and were observed to attack and bite small-mouthed and blue-spotted salamander larvae in mesocosms. Unisexual larvae were competitively superior to blue-spotted salamander larvae, but competitively equal to small-mouthed salamander larvae. Laboratory experiments confirmed field observations that both species increased their use of refuges in the presence of unisexual larvae and that this behavior resulted in niche partitioning. Blue-spotted salamander larvae were less active in the presence of unisexuals; however, small-mouthed larvae increased activity and use of refuges in the presence of larger intraguild predators. The hypothesis that microhabitat partitioning and altered activities minimize the effects of competition and predation was supported.