Comparative Life Histories of Two Sympatric Ambystoma Species at a Breeding Pond in Massachusetts1

Abstract

Spotted Salamanders (Ambystoma maculatum) and members of the Blue-Spotted Salamander complex (Ambystoma laterale-jeffersonianum complex) often share terrestrial and wetland habitats, allowing controlled comparison of their life-history strategies. We examined population sizes, sex ratios, breeding frequencies, recruitment rates, and age structures, in sympatric populations of Spotted Salamanders and members of the Blue-Spotted Salamander complex across five years. We saw declines in breeding population size that were larger for Blue-Spotted Salamanders than for Spotted Salamanders (55.2% vs. 33.3%), although members of the Blue-Spotted Salamander complex consistently had larger breeding populations. However, members of the Blue-Spotted Salamander complex also had more highly skewed sex ratios than did Spotted Salamanders (female : male, mean , 23:1 vs. 0.8:1), greater intervals between breeding, lower recruitment (0.9 vs. 5.7 juveniles/female/year), and a younger average age (3.7 vs. 5.2 years). In addition, the sex ratio of Blue- Spotted Salamanders became more skewed over time, with a dramatic reduction in the number of males. Much of our demographic data at this site suggest that the lower reproductive success of Blue-Spotted Salamanders may reduce the relative likelihood of their persistence compared to Spotted Salamanders. However, yearly breeding population sizes, reproductive ages, and lack of juvenile demographic data imply that more study is needed to understand the relative likelihood of persistence for these two groups of pond- breeding amphibians.