Investigation of the amphibian decline phenomenon: Novel small-scale factors and a large-scale overview

by Karraker, Nancy E., Ph.D., STATE UNIVERSITY OF NEW YORK COL. OF ENVIRONMENTAL SCIENCE & FORESTRY, 2007, 179 pages; 3258375


Declines and extinctions of amphibians are being reported worldwide at an increasing rate. Habitat loss, disease, climate change, and invasive species are responsible for many, but others remain unexplained. The objectives of my research were to evaluate patterns in ecological traits and human-related disturbances against conservation status for amphibians of the United States; (2) examine the effects of road deicing salt on survival of spotted salamanders (Ambystoma maculatum), green frogs (Rana clamitans ), and wood frogs (Rana sylvatica); and (3) determine the relative importance of beaver ponds and vernal pools to amphibian production.

I compiled data on ecological traits for 229 amphibian species and disturbance-related parameters and evaluated them against conservation status. No particular ecological traits were associated with imperiled frogs, but imperiled frogs tended to have < 18% cropland within their ranges. Imperiled salamanders had clutch sizes < 51, range sizes < 21,000 km2, and human densities < 200 per km2 within their ranges.

I evaluated the effects of road salt on amphibians in vernal pools. I measured water quality and censused egg masses of wood frogs and spotted salamanders in roadside and non-roadside pools. Embryos and larvae of these two species and green frogs were exposed to ecologicallyrelevant conductivity levels. Survival in embryonic and larval spotted salamanders was reduced at conductivity levels of 500 μS (145 mg/L chloride) and 3000 μS (945 mg/L chloride), but was affected only at the higher level in wood frogs. Survival in green frogs was > 90% in embryos and > 85% in larvae in all treatments.

I used 65 vernal pools and 37 beaver ponds to determine the relative importance of each to amphibian production. I censused wetlands for wood frog egg masses and installed pitfall traps to capture metamorphs. Survival to metamorphosis and metamorph production were compared between the two wetland types. Survival to metamorphosis and metamorph production were an order of magnitude lower in vernal pools, and metamorphs from beaver ponds were 1.3 times larger.

While unexplained amphibian declines require immediate attention, other factors causing declines, such as habitat loss and environmental contaminants, should also remain conservation priorities.

Key words. amphibian declines, macroecology, conservation status, road deicing salt, Ambystoma maculatum, Rana clamitans, Rana sylvatica, production, beaver pond, vernal pool.

AdviserJames P. Gibbs
Source TypeDissertation
SubjectsEcology; Environmental science
Publication Number3258375

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