Activity level and the tradeoff between growth and survival in the salamanders Ambystoma jeffersonianum and Hemidactylium scutatum

Activity level is often positively correlated with both growth rate and vul nerability to predation, creating a fitness tradeoff. Ambystoma jeffersonia num and Hemidactylium scutatum, two sympatric species of salamanders with v ery different larval growth rates, were assayed for differences in activity level and vulnerability to predation In a laboratory assay, A. jeffersonia num, the higher growth rate species, had a significantly higher activity le vel early in the larval period, which is when larval mortality is expected to be greatest. In an artificial pond experiment with a salamander predator (adults of Notophthalmus viridescens), A. jeffersonianum had poor initial survival, whereas H. scutatum had a constant mortality rate. Survival of bo th species was similar at the time H. scutatum metamorphosed. The presence of predators tended to cause all increase in growth rate in A. jeffersonian um, but a decrease in H. scutatum. Lanae of neither species reduced total a ctivity when in the presence of a predator through day 12 of their larval p eriods. After day 12, H. scutatum increased total activity when in a predat or-free environment, but reduced total activity when in the presence of a p redator. This study demonstrated that the activity level pattern of A. jeff ersonianum early in the lan al period was more successful when integrating both survival and growth in the presence of a predator and may help to expl ain the greater relative abundance of that species in predator-filled aquat ic habitats.