Consequences of forest fragmentation for juvenile survival in spotted (Ambystoma maculatum) and marbled (Ambystoma opacum) salamanders

Abstract

We compared demographic traits of postmetamorphic salamanders among old fields, forest interior, and edge habitats over 2 years. Recently metamorphosed spotted salamanders ( Ambystoma maculatum (Shaw, 1802)) and marbled salamanders ( Ambystoma opacum (Gravenhorst, 1807)) were individually marked, added to terrestrial enclosures, and recaptured in pitfall traps. Proportion known alive in the fields was <5% by the first fall and declined to 0% for both species in the 2nd year. In forested enclosures, significantly more A. opacum (mean 38.5%) and A. maculatum (mean 16.7%) survived until the first fall and several individuals of each species attained sexual maturity. Mean proportion known alive was approximately two times higher in A. opacum than in A. maculatum, perhaps because of an advantage of earlier metamorphosis in A. opacum. Our results indicate that the first few months in the terrestrial environment is a critical period which determines survival between metamorphosis and first reproduction. Juveniles that weighed more initially had greater chances of surviving this period. We found no evidence that proximity to forest edges incurred fitness costs in terms of reduced growth or survival for juvenile ambystomatids. Because no juveniles survived to maturity in fields, breeding sites surrounded by non-forested habitat may be population sinks for these species.