The Effect of Larval Density on Adult Demographic Traits in Ambystoma Opacum

Abstract

Factors that affect traits of aquatic larvae of amphibians may have long—lasting effects on terrestrial juveniles and adults. I manipulated larval densities of marbled salamanders, Ambystoma opacum, in large—scale field enclosures during 2 yr, released the juveniles that metamorphosed from these enclosures, and tested for effects on adults that returned to the pond during 6—7 subsequent breeding seasons. Individuals from low larval density treatments tended to have greater lipid stores at metamorphosis than those from high densities and survived longer in a laboratory inanition study. In the field, individuals that experienced low larval density returned for their first reproductive bout as larger adults than those from high—density treatments. For 5—yr—old females released in 1986, low larval density was linked to greater clutch size; clutch size in 4—yr—old animals from the 1987 cohort did not differ between larval treatment groups. Larval density also influenced age at first reproduction, as animals reared at low densities returned to breed at younger ages. Averaged across both cohorts, the proportion of animals that returned to breed at least once was 21% for low—density groups compared to 6% for the high—density groups. The larval environment exerted a strong influence on postmetamorphic traits, and thus larval density likely plays an important role in population regulation in both the aquatic and terrestrial phase of the life cycle.