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

—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 BlueSpotted 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 pondbreeding amphibians. Amphibian declines and extinctions are occurring worldwide (reviewed by Blaustein and Wake, 1990; Wyman, 1990; Bury, 1999). Although distinguishing between declines and natural population fluctuations without longterm studies may be difficult (e.g., Pechmann et al., 1991; Reed and Blaustein, 1995), the mechanisms contributing to some particular species’ declines have been identified. Mechanisms include introduced species (Gamradt and Kats, 1996), increased UV-B radiation (Blaustein et al., 1994), pathogen outbreaks (Kiesecker et al., 2001), and pollution (Hopkins et al., 1997). Possibly the most prevalent mechanism, however, is habitat fragmentation (deMaynadier and Hunter, 1998, 1999; Clark et al., in press) and loss (Wyman, 1990; Blaustein et al., 1994; Pounds et al., 1999; Homan et al., 2004). Habitat loss may be a particularly important concern for amphibian species that use both aquatic and terrestrial habitats during their life cycle because it can impact both habitats (Duellman and Trueb, 1986; Windmiller, 1996; Petranka, 1998). Mole Salamanders (Ambystoma spp.), for example, spend the majority of their time in terrestrial habitats surrounding breeding wetlands. Although partial habitat loss can cause population declines, the details of how active habitat loss affects demographic traits are poorly studied. In addition, a population’s capacity to recover from a sudden decline, regardless of its cause, is affected in part by demographic traits such as age structure, sex ratio, and breeding frequency. We studied demographic characteristics of two sympatric Ambystoma species, Spotted Salamanders (Ambystoma maculatum) and members of a Blue-Spotted Salamander (Ambystoma laterale-jeffersonianum) complex. These species spend more than 11 months of the year in upland forest habitat surrounding their breeding ponds, to which they show high fidelity (Downs, 1989a,b; Windmiller, 1996; Regosin et al., 2005). Spotted Salamander demography and ecology are fairly well studied, including research on time intervals between breeding, fecundity, recruitment, age structure, survivorship, and habitat requirements and patterns of use (e.g., Husting, 1965; Flageole and Leclair, 1992; Blackwell et al., 2004; Porej et al., 2004). The Blue-Spotted Salamander complex is more poorly studied (e.g., Clanton, 1934; Uzzell, 1964; Wilbur, 1971, 1977), with most research focusing on reproduction (Bogart and Licht, 1986; Lowcock et al., 1991; Lowcock, 1994). As commonly occurs with Blue-Spotted Salamanders, our study population coexisted with primarily 1 Howard Whiteman served as editor for this manuscript. 3 Corresponding Author. Present address: Department of Biology, Denison University, Granville, Ohio 43023, USA; E-mail: [email protected] Journal of Herpetology, Vol. 41, No. 3, pp. 401–409, 2007 Copyright 2007 Society for the Study of Amphibians and Reptiles