▪ Abstract Declines and losses of amphibian populations are a global problem with complex local causes. These may include ultraviolet radiation, predation, habitat modification, environmental acidity and toxicants, diseases, changes in climate or weather patterns, and interactions among these factors. Understanding the extent of the problem and its nature requires an understanding of how local factors affect the dynamics of local populations. Hypotheses about population behavior must be tested against appropriate null hypotheses. We generated null hypotheses for the behavior of amphibian populations using a model, and we used them to test hypotheses about the behavior of 85 time series taken from the literature. Our results suggest that most amphibian populations should decrease more often than they increase, due to highly variable recruitment and less variable adult mortality. During the period covered by our data (1951–1997), more amphibian populations decreased than our model predicted. However, there ...

/pdf/global-amphibian-declines-a-problem-in-applied-ecology-22m177jgsq.pdf

Global Amphibian Declines: A Problem in Applied Ecology

As part of an overall 'biodiversity crisis', many amphibian populations are in decline throughout the world. Numerous factors have contributed to these declines, including habitat destruction, pathogens, increasing ultraviolet (UV) radiation, introduced non-native species and contaminants. In this paper we review the contribution of increasing UV radiation and environmental contamination to the global decline of amphibian populations. Both UV radiation and environmental contaminants can affect amphibians at all life stages. Exposure to UV radiation and to certain contaminants can kill amphibians and induce sublethal affects in embryos, larvae and adults. Moreover, UV radi- ation and contaminants may interact with one another synergistically. Synergistic interactions of UV radiation with contaminants can enhance the detrimental effects of the contaminant and UV radiation.

/pdf/ultraviolet-radiation-toxic-chemicals-and-amphibian-b2ok5bzecb.pdf

Ultraviolet radiation, toxic chemicals and amphibian population declines

As part of an overall decline in biodiversity, populations of many organisms are declining and species are being lost at unprecedented rates around the world. This includes many populations and species of amphibians. Although numerous factors are affecting amphibian populations, we show potential direct and indirect effects of climate change on amphibians at the individual, population and community level. Shifts in amphibian ranges are predicted. Changes in climate may affect survival, growth, reproduction and dispersal capabilities. Moreover, climate change can alter amphibian habitats including vegetation, soil, and hydrology. Climate change can influence food availability, predator-prey relationships and competitive interactions which can alter community structure. Climate change can also alter pathogen-host dynamics and greatly influence how diseases are manifested. Changes in climate can interact with other stressors such as UV-B radiation and contaminants. The interactions among all these factors are complex and are probably driving some amphibian population declines and extinctions.

/pdf/direct-and-indirect-effects-of-climate-change-on-amphibian-5foh43p4z6.pdf

Direct and Indirect Effects of Climate Change on Amphibian Populations

There has been a great deal of recent attention on the suspected increase in amphibian deformities. However, most reports of amphibian deformities have been anecdotal, and no experiments in the field under natural conditions have been performed to investigate this phenomenon. Under laboratory conditions, a variety of agents can induce deformities in amphibians. We investigated one of these agents, UV-B radiation, in field experiments, as a cause for amphibian deformities. We monitored hatching success and development in long-toed salamanders under UV-B shields and in regimes that allowed UV-B radiation. Embryos under UV-B shields had a significantly higher hatching rate and fewer deformities, and developed more quickly than those exposed to UV-B. Deformities may contribute directly to embryo mortality, and they may affect an individual’s subsequent survival after hatching.

https://www.pnas.org/content/pnas/94/25/13735.full.pdf

Ambient UV-B radiation causes deformities in amphibian embryos

It is well established that a decrease in genetic variation can lead to reduced fitness and lack of adaptability to a changing environment. Amphibians are declining on a global scale, and we present a four-point argument as to why this taxonomic group seems especially prone to such genetic processes. We elaborate on the extent of recent fragmentation of amphibian gene pools and we propose the term dissociated populations to describe the residual population structure. To put their well-documented loss of genetic diversity into context, we provide an overview of 34 studies (covering 17 amphibian species) that address a link between genetic variation and >20 different fitness traits in amphibians. Although not all results are unequivocal, clear genetic-fitness-correlations (GFCs) are documented in the majority of the published investigations. In light of the threats faced by amphibians, it is of particular concern that the negative effects of various pollutants, pathogens and increased UV-B radiation are magnified in individuals with little genetic variability. Indeed, ongoing loss of genetic variation might be an important underlying factor in global amphibian declines.

/pdf/global-amphibian-declines-loss-of-genetic-diversity-and-3bwl9lyhhl.pdf

Global Amphibian Declines, Loss of Genetic Diversity and Fitness: A Review

Many amphibian species, in widely scattered locations, currently show population declines and/or reductions in range, but other amphibian species show no such declines. There is no known single cause for these declines. Differential sensitivity to UVB radiation among species might be one contributing factor. We have focused on amphibian eggs, potentially the most UVB-sensitive stage, and compared their resistance to UVB components of sunlight with their levels of photolyase, typically the most important enzyme for repair of the major UV photoproducts in DNA, cyclobutane pyrimidine dimers. Photolyase varied 100-fold among eggs/oocytes of 10 species. Among three species-Hyla regilla, Rana cascadae, and Bufo boreas-for which resistance of eggs to solar UVB irradiance in their natural locations was measured, hatching success correlated strongly with photolyase. Two additional species, Rana aurora and Ambystoma gracile, now show similar correlations. Among the low-egg-photolyase species, R. cascadae and B. boreas are showing declines, and the status of A. gracile is not known. Of the two high-photolyase species, populations of H. regilla remain robust, but populations of R. aurora are showing declines. To determine whether levels of photolyase or other repair activities are affected by solar exposures during amphibian development, we have initiated an extended study of H. regilla and R. cascadae, and of Xenopus laevis, laboratory-reared specimens of which previously showed very low photolyase levels. Hyla regilla and R. cascadae tadpoles are being reared to maturity in laboratories supplemented with modest levels of UV light or light filtered to remove UVB wavelengths. Young X. laevis females are being reared indoors and outdoors. Initial observations reveal severe effects of both UVA and UVB light on H. regilla and R. cascadae tadpoles and metamorphs, including developmental abnormalities and high mortalities. Assays of photolyase levels in the skins of young animals roughly parallel previous egg/oocyte photolyase measurements for all three species.

Developmental responses of amphibians to solar and artificial UVB sources: a comparative study.

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Developmental responses of amphibians to solar and artificial UVB sources: a comparative study.