Previous research on habitat associations of pond-breeding amphibians has used community assemblages as response variables because the intensive labor required to quantify population size is usually prohibitive. However, wood frogs (Rana sylvatica) and spotted salamanders (Ambystoma maculatum) oviposit egg masses that can be surveyed rapidly; thus, we were able to quantify the influence of within-pond parameters on their annual breeding effort. During 2000–2001, we assessed the effects of hydroperiod, within-pond vegetation, canopy closure, hydrologic isolation, fish occurrence, and pond size on egg mass counts of wood frogs and spotted salamanders at 124 ponds in western Rhode Island. Study sites were stratified by road density, which served as an indirect measure of non-breeding habitat quality and quantity. Hydroperiod had a significant influence on annual breeding effort. Egg masses of both species were most abundant in seasonal ponds that dried between 1 August and 30 November. Breeding populations of spotted salamanders were smaller in ponds that dried before the end of July, whereas breeding populations of wood frogs were reduced in ponds that did not dry during our two-year study. Both species usually attached egg masses to shrubs or branches in shallow water near the water surface, which may explain why both species oviposited more egg masses in ponds with substantial vegetation complexity, including extensive coverage by shrubs and persistent non-woody vegetation. Although wood frogs were more likely than spotted salamanders to avoid ovipositing in ponds with fish, egg mass counts of both species were substantially reduced in ponds containing fish. Numbers of egg masses for spotted salamanders and wood frogs were similar between larger ponds and those as small as 0.05 ha and 0.15 ha, respectively. Previously, researchers proposed protecting isolated wetlands > 0.2 ha to sustain populations of pond-breeding amphibians, but our research suggests that wetlands as small as 0.05 ha may provide critical breeding habitat for some species in southern New England.
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Vol. 24 • No. 1