Habitat Correlates of Reproductive Effort in Wood Frogs and Spotted Salamanders in an Urbanizing Watershed

Peter W C Paton,Dennis E Skidds,Jonathan C Mitchell,Francis C Golet

doi:10.1670/0022-1511(2007)41[439:hcorei]2.0.co;2

Abstract

Wildlife biologists and managers are concerned about the effects of forest fragmentation and habitat loss on pond-breeding amphibian populations. Most research has assessed the effects of habitat composition at multiple spatial scales on the presence or absence of amphibians at breeding ponds. We were interested in the effects of habitat characteristics on amphibian population size and used Wood Frog (Rana sylvatica) and Spotted Salamander (Ambystoma maculatum) egg mass counts as an index. Between 2001 and 2005, we monitored 65 seasonal ponds within forested landscapes in the Pawcatuck River watershed of Rhode Island. Both species were detected in at least 88% of the ponds sampled. Egg mass counts for both species were highest in ponds that usually dried between early October and late November. Wood Frog egg mass numbers were positively associated with pond hydroperiod, size, and depth; location on glacial fluvial deposits; the extent of persistent nonwoody plant cover in ponds; and the area of upland forest within 1 km of the pond edge. Egg mass numbers were negatively associated with location on alluvium or dense till deposits, percent canopy cover, the number of buildings within 1 km, and the area of residential development within 1 km. Spotted Salamander egg mass counts were positively associated with pond hydroperiod, size, and depth, and upland forest area within 1 km. They were negatively related to location on alluvium. Multivariate models developed from within-pond variables explained more variation in egg mass counts for both species than those developed from landscape-level factors, but the best combined models suggested that habitat characteristics at both scales are useful in the prediction of breeding effort at individual sites. Given the continuing urbanization of southern New England and the ineffectiveness of wetland regulations in protecting required terrestrial habitat around seasonal ponds, proactive techniques also are required to assure the maintenance of pond-breeding amphibian populations.

Highlights

Despite the increasing evidence that landscape-level habitat characteristics influence amphibian community composition, few researchers have conducted empirical studies investigating amphibian population sizes in heterogeneous, human-dominated landscapes across a wide geographic range (Laan and Verboom, 1990; Vos and Chardon, 1998; Lehtinen et al, 1999; Homan et al, 2004)
We developed a number of multivariate regression models using within-pond and landscape-scale habitat characteristics to account for the variation observed in Wood Frog and Spotted Salamander egg mass counts at 65 seasonal forest ponds in the Pawcatuck River watershed of southern Rhode Island
Models composed solely of within-pond characteristics accounted for more variation in Wood Frog egg mass counts Spotted Salamander counts

Summary

Introduction

Despite the increasing evidence that landscape-level habitat characteristics influence amphibian community composition, few researchers have conducted empirical studies investigating amphibian population sizes in heterogeneous, human-dominated landscapes across a wide geographic range (Laan and Verboom, 1990; Vos and Chardon, 1998; Lehtinen et al, 1999; Homan et al, 2004). Wood Frogs and Spotted Salamanders deposit large, globular egg masses that are relatively easy to survey compared to other amphibian species in the northeastern United States. We developed a number of multivariate regression models using within-pond and landscape-scale habitat characteristics to account for the variation observed in Wood Frog and Spotted Salamander egg mass counts at 65 seasonal forest ponds in the Pawcatuck River watershed of southern Rhode Island. These models were subsequently evaluated using an information-theoretic model selection framework (Burnham and Anderson, 2002). Such models can be used to identify key factors that influence the abundance of amphibians and could be used by state and federal regulators, municipal conservation commissions, land trusts, and environmental consultants to identify specific areas of high amphibian abundance for conservation

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Conclusion