With rare exceptions, anuran larvae have traditionally been considered to occupy lower trophic levels in aquatic communities where they function as microphagous suspension feeders. This view is being challenged by studies showing that tadpoles with generalized morphology often function as macrophagous predators. Here, we review the literature concerning macrophagy by tadpoles and provide two additional examples involving generalized tadpoles. In the first, we demonstrate with laboratory and field experiments that wood frog (Rana sylvatica) tadpoles are major predators of macroinvertebrates in ponds. In the second, we show that green frog (R. clamitans) tadpoles can cause catastrophic reproductive failure of the wood frog via egg predation. These results and data from other studies challenge the assumption that generalized tadpoles function as filter-feeding omnivores, and question the general applicability of community organization models which assume that predation risk increases with pond permanence. We suggest that predation risk is greater in temporary ponds than in more permanent ponds for many organisms that are vulnerable to predation by tadpoles. This being so, a conditional model based upon interactions that are species-specific, life-stage-specific, and context-dependent may better explain community organization along hydrological gradients than models which assume that temporary ponds have few or no predators.

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Studies suggest that increased ground-level UV-B radiation due to stratospheric ozone depletion is adversely affecting many aquatic organisms. In particular, ambient UV-B radiation can kill or deform amphibian embryos and may be contributing to global amphibian declines. Sensitivity tests have been conducted primarily at northern latitudes ( Ͼ 42 Њ N), where ozone thinning is most prevalent. Studies in southern California and Spain, however, suggest that some amphibians are vulnerable to ambient UV-B at these lower latitudes. We tested the sensitivity of pond-breeding amphibians to UV-B radiation in the southern Appalachian Mountains (35 Њ N; 660 m) of the United States, where stratospheric ozone has declined during the last two decades. We exposed eggs of frogs ( Hyla chrysoscelis , Pseudacris triseriata , Rana sylvatica ) and a salamander ( Ambystoma maculatum ) to three treatments under field conditions that provided maximum exposure to solar radiation: (1) a polycarbonate filter that blocks Ͼ 98% of UV-B (2) an acrylic filter that transmits 80% of UV-B, and (3) unfiltered sunlight. Survivorship to hatching (grand mean ϭ 91%) and the percentage of embryos deformed (grand mean ϭ 4.4%) did not differ significantly among treatments for any species, but differences in the percentage of embryos deformed approached statistical significance for Hyla ( p ϭ 0.06) and Pseudacris ( p ϭ 0.10). More refined analyses using orthogonal contrasts revealed that deformity rates for both species were significantly lower in embryos that were shielded from UV-B than in unshielded controls. A pooled analysis of all anurans also indicated that deformity rates were higher in treatments with UV-B transmitting plates than in those with blocking plates. Collectively, our data suggest that pond-breeding amphibians in the southern Appalachians currently incur only slight risk from exposure to ambient UV-B radiation. If ground-level radiation increases in the future, the risk for certain species could increase significantly. (25 Њ N; 660m), donde el ozono estratosférico ha disminído durante las dos últimas décadas. Expusimos huevos de ranas ( Hyla chrysoscelis , Pseudacris triseriata , Rana sylvatica ) y de la salamandra ( Ambystoma maculatum ) a tres tratamientos bajo condiciones de campo que provéian una exposición máxima de radiación solar de: (1) un filtro de policarbonato que bloquea Ͼ 98% de UV-B, (2) un filtro de acrílico que transmite 80% de la UV-B y (3) luz solar sin filtrar. La supervivencia de las crías (gran media ϭ 91%) y el porcentaje de embriones deformes (gran media ϭ 4.4%) no difirieron significativamente entre tratamientos para ninguna de las especies. Sin embargo, diferencias en el porcentaje de embriones deformes aproximó la significancia estadística para Hyla ( p ϭ 0.06) y Pseudacris ( p ϭ 0.10). Análisis más refinados utilizando contrastes ortogonales revelaron que las tasas de deformidad para ambas especies fue significativamente menor en embriones que estuvieron protegidos de la UV-B en comparación con los desprote...

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