Measuring the meltdown: drivers of global amphibian extinction and decline

Habitat loss, climate change, over-exploitation, disease and other factors have been hypothesised in the global decline of amphibian biodiversity. However, the relative importance of and synergies among different drivers are still poorly understood. We present the largest global analysis of roughly 45% of known amphibians (2,583 species) to quantify the influences of life history, climate, human density and habitat loss on declines and extinction risk. Multi-model Bayesian inference reveals that large amphibian species with small geographic range and pronounced seasonality in temperature and precipitation are most likely to be Red-Listed by IUCN. Elevated habitat loss and human densities are also correlated with high threat risk. Range size, habitat loss and more extreme seasonality in precipitation contributed to decline risk in the 2,454 species that declined between 1980 and 2004, compared to species that were stable (n = 1,545) or had increased (n = 28). These empirical results show that amphibian species with restricted ranges should be urgently targeted for conservation.     

Amphibian decline and extinction: what we know and what we need to learn

For over 350 million yr, thousands of amphibian species have lived on Earth. Since the 1980s, amphibians have been disappearing at an alarming rate, in many cases quite suddenly. What is causing these declines and extinctions? In the modern era (post 1500) there are 6 leading causes of biodiversity loss in general, and all of these acting alone or together are responsible for modern amphibian declines: commercial use; introduced/exotic species that compete with, prey on, and parasitize native frogs and salamanders; land use change; contaminants; climate change; and infectious disease. The first 3 causes are historical in the sense that they have been operating for hundreds of years, although the rate of change due to each accelerated greatly after about the mid-20th century. Contaminants, climate change, and emerging infectious diseases are modern causes suspected of being responsible for the so-called 'enigmatic decline' of amphibians in protected areas. Introduced/exotic pathogens, land use change, and infectious disease are the 3 causes with a clear role in amphibian decline as well as extinction; thus far, the other 3 causes are only implicated in decline and not extinction. The present work is a review of the 6 causes with a focus on pathogens and suggested areas where new research is needed. Batrachochytrium dendrobatidis (Bd) is a chytrid fungus that is an emerging infectious disease causing amphibian population decline and species extinction. Historically, pathogens have not been seen as a major cause of extinction, but Bd is an exception, which is why it is such an interesting, important pathogen to understand. The late 20th and early 21st century global biodiversity loss is characterized as a sixth extinction event. Amphibians are a striking example of these losses as they disappear at a rate that greatly exceeds historical levels. Consequently, modern amphibian decline and extinction is a lens through which we can view the larger story of biodiversity loss and its consequences.     

Global amphibian declines: sorting the hypotheses

Abstract. Reports of malformed amphibians and global amphibian declines have led to public concern, particularly because amphibians are thought to be indicator species of overall environmental health. The topic also draws scientific attention because there is no obvious, simple answer to the question of what is causing amphibian declines? Complex interactions of several anthropogenic factors are probably at work, and understanding amphibian declines may thus serve as a model for understanding species declines in general. While we have fewer answers than we would like, there are six leading hypotheses that we sort into two classes. For class I hypotheses, alien species, over‐exploitation and land use change, we have a good understanding of the ecological mechanisms underlying declines; these causes have affected amphibian populations negatively for more than a century. However, the question remains as to whether the magnitude of these negative effects increased in the 1980s, as scientists began to notice a global decline of amphibians. Further, remedies for these problems are not simple. For class II hypotheses, global change (including UV radiation and global climate change), contaminants and emerging infectious diseases we have a poor, but improving understanding of how each might cause declines. Class II factors involve complex and subtle mechanistic underpinnings, with probable interactions among multiple ecological and evolutionary variables. They may also interact with class I hypotheses. Suspected mechanisms associated with class II hypotheses are relatively recent, dating from at least the middle of the 20th century. Did these causes act independently or in concert with pre‐existing negative forces of class I hypotheses to increase the rate of amphibian declines to a level that drew global attention? We need more studies that connect the suspected mechanisms underlying both classes of hypotheses with quantitative changes in amphibian population sizes and species numbers. An important step forward in this task is clarifying the hypotheses and conditions under which the various causes operate alone or together.     

Threat to the point: improving the value of comparative extinction risk analysis for conservation action

Comparative extinction risk analysis is a common approach for assessing the relative plight of biodiversity and making conservation recommendations. However, the usefulness of such analyses for conservation practice has been questioned. One reason for underperformance may be that threats arising from global environmental changes (e.g., habitat loss, invasive species, climate change) are often overlooked, despite being widely regarded as proximal drivers of species’ endangerment. We explore this problem by (i) reviewing the use of threats in this field and (ii) quantitatively investigating the effects of threat exclusion on the interpretation and potential application of extinction risk model results. We show that threat variables are routinely (59%) identified as significant predictors of extinction risk, yet while most studies (78%) include extrinsic factors of some kind (e.g., geographic or bioclimatic information), the majority (63%) do not include threats. Despite low overall usage, studies are increasingly employing threats to explain patterns of extinction risk. However, most continue to employ methods developed for the analysis of heritable traits (e.g., body size, fecundity), which may be poorly suited to the treatment of nonheritable predictors including threats. In our global mammal and continental amphibian extinction risk case studies, omitting threats reduced model predictive performance, but more importantly (i) reduced mechanistic information relevant to management; (ii) resulted in considerable disagreement in species classifications (12% and 5% for amphibians and mammals, respectively, translating to dozens and hundreds of species); and (iii) caused even greater disagreement (20–60%) in a downstream conservation application (species ranking). We conclude that the use of threats in comparative extinction risk analysis is important and increasing but currently in the early stages of development. Priorities for future studies include improving uptake, availability, quality and quantification of threat data, and developing analytical methods that yield more robust, relevant and tangible products for conservation applications.     

Plant extinction risk under climate change: are forecast range shifts alone a good indicator of species vulnerability to global warming?

Models that couple habitat suitability with demographic processes offer a potentially improved approach for estimating spatial distributional shifts and extinction risk under climate change. Applying such an approach to five species of Australian plants with contrasting demographic traits, we show that: (i) predicted climate‐driven changes in range area are sensitive to the underlying habitat model, regardless of whether demographic traits and their interaction with habitat patch configuration are modeled explicitly; and (ii) caution should be exercised when using predicted changes in total habitat suitability or geographic extent to infer extinction risk, because the relationship between these metrics is often weak. Measures of extinction risk, which quantify threats to population persistence, are particularly sensitive to life‐history traits, such as recruitment response to fire, which explained approximately 60% of the deviance in expected minimum abundance. Dispersal dynamics and habitat patch structure have the strongest influence on the amount of movement of the trailing and leading edge of the range margin, explaining roughly 40% of modeled structural deviance. These results underscore the need to consider direct measures of extinction risk (population declines and other measures of stochastic viability), as well as measures of change in habitat area, when assessing climate change impacts on biodiversity. Furthermore, direct estimation of extinction risk incorporates important demographic and ecosystem processes, which potentially influence species’ vulnerability to extinction due to climate change.     

Amphibians as models for studying environmental change

The use of amphibians as models in ecological research has a rich history. From an early foundation in studies of amphibian natural history sprang generations of scientists who used amphibians as models to address fundamental questions in population and community ecology. More recently, in the wake of an environment that human disturbances rapidly altered, ecologists have adopted amphibians as models for studying applied ecological issues such as habitat loss, pollution, disease, and global climate change. Some of the characteristics of amphibians that make them useful models for studying these environmental problems are highlighted, including their trophic importance, environmental sensitivity, research tractability, and impending extinction. The article provides specific examples from the recent literature to illustrate how studies on amphibians have been instrumental in guiding scientific thought on a broad scale. Included are examples of how amphibian research has transformed scientific disciplines, generated new theories about global health, called into question widely accepted scientific paradigms, and raised awareness in the general public that our daily actions may have widespread repercussions. In addition, studies on amphibian declines have provided insight into the complexity in which multiple independent factors may interact with one another to produce catastrophic and sometimes unpredictable effects. Because of the complexity of these problems, amphibian ecologists have been among the strongest advocates for interdisciplinary research. Future studies of amphibians will be important not only for their conservation but also for the conservation of other species, critical habitats, and entire ecosystems.     

Clade‐specific consequences of climate change to amphibians in Atlantic Forest protected areas

The rapid global decline of amphibian population is alarming because many occur for apparently unknown or enigmatic reasons, even inside protected areas (PAs). Some studies have predicted the effects of climate change on amphibians’ distribution and extinction, but the relationship and consequences of climate change to the phylogenetic structure of amphibian assemblages remain obscure. By applying robust techniques for ecological niche modeling and a cutting‐edge approach on community phylogenetics, here, we evaluate how climate change affects the geographical pattern of amphibian species richness and phylogenetic diversity in the Atlantic Forest Biodiversity Hotspot, Brazil, as well as how the phylogenetic composition of amphibian assemblages respond to climate change. We found that most species contracted their ranges and that such responses are clade specific. Basal amphibian clades (e.g. Gymnophiona and Pipidae) were positively affected by climate change, whereas late‐divergent clades (e.g. Cycloramphidae, Centrolenidae, Eleutherodactylidae, Microhylidae) were severely impacted. Identifying major changes in the phylogenetic pool represents a first step towards a better understanding of how assembly processes related to climate change will affect ecological communities. A deep analysis of the impacts of climate change not only on species, but also on the evolutionary relationships among species might foster the discussion on clade‐level conservation priorities for this imperiled fauna.     

Individualistic Population Responses of Five Frog Species in Two Changing Tropical Environments over Time

Roughly 40% of amphibian species are in decline with habitat loss, disease, and climate change being the most cited threats. Heterogeneity of extrinsic (e.g. climate) and intrinsic (e.g. local adaptations) factors across a species’ range should influence population response to climate change and other threats. Here we examine relative detectability changes for five direct-developing leaf litter frogs between 42-year sampling periods at one Lowland Tropical Forest site (51 m.a.s.l.) and one Premontane Wet Forest site (1100 m.a.s.l.) in southwest Costa Rica. We identify individualistic changes in relative detectability among populations between sampling periods at different elevations. Both common and rare species showed site-specific declines, and no species exhibited significant declines at both sites. Detection changes are correlated with changes in temperature, dry season rainfall, and leaf litter depth since1969. Our study species share Least Concern conservation status, life history traits, and close phylogenetic relationship, yet their populations changed individualistically both within and among species. These results counter current views of the uniformity or predictability of amphibian decline response and suggest additional complexity for conservation decisions.     

A general assessment of the conservation status and decline trends of Mexican amphibians

We present a review on the conservation status and population trends of the 372 amphibian species currently recognized for Mexico. We based our analyses on the information gathered by the International Union for the Conservation of Nature-the Global Amphibian Assessment (IUCN-GAA) as well as on available literature about imminent or potential threats to these organisms in Mexico. This country has the fifth largest amphibian fauna in the world and almost 58% of the species that inhabit this country are considered as threatened. We highlight the proportion of species per order, family, and genus that are currently under severe risk in Mexico. In addition, we prepared a detailed list of the main factors that are threatening amphibians in this country. Evidence is provided that the six main mechanisms that are globally leading amphibians to extinction (alien species, over-exploitation, land use change, global changes, pollution, and infectious diseases) are indeed currently operating in Mexico. We discuss the relative importance of each of these causes. We also highlight the paucity of quantitative studies that support the current conservation status of Mexican amphibian species.     

Do hormone‐modulating chemicals impact on reproduction and development of wild amphibians?

Globally, amphibians are undergoing a precipitous decline. At the last estimate in 2004, 32% of the approximately 6000 species were threatened with extinction and 43% were experiencing significant declines. These declines have been linked with a wide range of environmental pressures from habitat loss to climate change, disease and pollution. This review evaluates the evidence that endocrine‐disrupting contaminants (EDCs) – pollutants that affect hormone systems – are impacting on wild amphibians and contributing to population declines. The review is limited to anurans (frogs and toads) as data for effects of EDCs on wild urodeles (salamanders, newts) or caecilians (limbless amphibians) are extremely limited. Evidence from laboratory studies has shown that a wide range of chemicals have the ability to alter hormone systems and affect reproductive development and function in anurans, but for the most part only at concentrations exceeding those normally found in natural environments. Exceptions can be found for exposures to the herbicide atrazine and polychlorinated biphenyls in leopard frogs (Rana pipiens) and perchlorate in African clawed frogs (Xenopus laevis). These contaminants induce feminising effects on the male gonads (including ‘intersex’ – oocytes within testes) at concentrations measured in some aquatic environments. The most extensive data for effects of an EDC in wild amphibian populations are for feminising effects of atrazine on male gonad development in regions across the USA. Even where strong evidence has been provided for feminising effects of EDCs, however, the possible impact of these effects on fertility and breeding outcome has not been established, making inference for effects on populations difficult. Laboratory studies have shown that various chemicals, including perchlorate, polychlorinated biphenyls and bromodiphenylethers, also act as endocrine disrupters through interfering with thyroid‐dependent processes that are fundamental for amphibian metamorphosis. Perchlorate has also been shown to induce these effects in wild anuran populations from perchlorate‐contaminated environments. Overall, the published data available suggest that some health effects observed in wild anuran populations, most notably intersex, likely have a chemical aetiology; however they derive only from very few anuran species and for a few pesticides at field sites in the USA. To understand better the impacts of EDCs on wild anuran populations, as well as other amphibian groups, assessment of fertility in exposed animals are required. Development of non‐destructive biomarkers that are indicative of specific EDC‐effect mechanisms are also needed to allow the study of vulnerable populations. This will help to distinguish the effects of EDCs from other environmental and/or genetic influences on development and reproduction.     

Complexity in conservation: lessons from the global decline of amphibian populations

As part of an overall "biodiversity crisis" many amphibian populations are in decline throughout the world. Numerous causes have been invoked to explain these declines. These include habitat destruction, climate change, increasing levels of ultraviolet radiation, environmental contamination, disease, and the introduction of non-native species. In this paper, we argue that amphibian population declines are caused by different abiotic and biotic factors acting together in a context-dependent fashion. Moreover, different species and different populations of the same species may react in different ways to the same environmental insult. Thus, the causes of amphibian population declines will vary spatially and temporally. Although some generalizations (e.g. those concerning environmental stress and disease outbreaks) can be made about amphibian population declines, we suggest that these generalizations take into account the context-dependent dynamics of ecological systems.     

两栖类栖息地的构建技术及效果评估

全球范围内两栖类的种类和数量急剧下降,栖息地面积减少和质量下降为重要原因之一.修复和重建两栖类栖息地是恢复两栖类种类和数量的重要手段.在城市化进程中,构建适宜的两栖类栖息地对两栖类的保护尤为关键.本研究选取上海市闵行区浦江镇的鲁汇苗木基地,于2014年5月-2016年9月开展两栖类栖息地的构建技术及效果评估研究.针对上海市常见的5种两栖类的生境需求,经过地形地貌改造、水系沟通调整和植被恢复等生态工程措施,构建了19 hm²两栖类栖息地.为评估两栖类栖息地的保护效果,采取样线法,选取5条100 m×5 m的调查样线,于多数两栖类的繁殖期(5-6月)和非繁殖期(8-9月)各调查1次,对比分析改造前(2014年)和改造后(2016年)两栖类的种类和数量.调查发现,改造前的繁殖期记录到两栖类4种,密度为(164.0±63.7) ind·hm^-2;非繁殖期4种,密度为(160.0±29.7) ind·hm^-2;改造后的繁殖期5种,密度为(560.0±159.3) ind·hm^-2;非繁殖期5种,密度为(628.0±186.2) ind·hm^-2.结果表明,通过构建适宜的两栖类栖息地,能够显著增加两栖类的种类和数量,具有较好的两栖类保护效果.本研究提出的两栖类栖息地的构建技术,为受损的两栖类栖息地的生态修复和重建以及城市林绿地的优化改造提供了参考案例.     

Dispersal and the metapopulation paradigm in amphibian ecology and conservation: are all amphibian populations metapopulations?

Amphibians are frequently characterized as having limited dispersal abilities, strong site fidelity and spatially disjunct breeding habitat. As such, pond‐breeding species are often alleged to form metapopulations. Amphibian species worldwide appear to be suffering population level declines caused, at least in part, by the degradation and fragmentation of habitat and the intervening areas between habitat patches. If the simplification of amphibians occupying metapopulations is accurate, then a regionally based conservation strategy, informed by metapopulation theory, is a powerful tool to estimate the isolation and extinction risk of ponds or populations. However, to date no attempt to assess the class‐wide generalization of amphibian populations as metapopulations has been made. We reviewed the literature on amphibians as metapopulations (53 journal articles or theses) and amphibian dispersal (166 journal articles or theses for 53 anuran species and 37 salamander species) to evaluate whether the conditions for metapopulation structure had been tested, whether pond isolation was based only on the assumption of limited dispersal, and whether amphibian dispersal was uniformly limited. We found that in the majority of cases (74%) the assumptions of the metapopulation paradigm were not tested. Breeding patch isolation via limited dispersal and/or strong site fidelity was the most frequently implicated or tested metapopulation condition, however we found strong evidence that amphibian dispersal is not as uniformly limited as is often thought. The frequency distribution of maximum movements for anurans and salamanders was well described by an inverse power law. This relationship predicts that distances beneath 11–13 and 8–9 km, respectively, are in a range that they may receive one emigrating individual. Populations isolated by distances approaching this range are perhaps more likely to exhibit metapopulation structure than less isolated populations. Those studies that covered larger areas also tended to report longer maximum movement distances – a pattern with implications for the design of mark‐recapture studies. Caution should be exercised in the application of the metapopulation approach to amphibian population conservation. Some amphibian populations are structured as metapopulations – but not all.     

Evaluation of assisted colonization strategies under global change for a rare,fire‐dependent plant

As a clear consensus is emerging that habitat for many species will dramatically reduce or shift with climate change, attention is turning to adaptation strategies to address these impacts. Assisted colonization is one such strategy that has been predominantly discussed in terms of the costs of introducing potential competitors into new communities and the benefits of reducing extinction risk. However, the success or failure of assisted colonization will depend on a range of population‐level factors that have not yet been quantitatively evaluated – the quality of the recipient habitat, the number and life stages of translocated individuals, the establishment of translocated individuals in their new habitat and whether the recipient habitat is subject to ongoing threats all will play an important role in population persistence. In this article, we do not take one side or the other in the debate over whether assisted colonization is worthwhile. Rather, we focus on the likelihood that assisted colonization will promote population persistence in the face of climate‐induced distribution changes and altered fire regimes for a rare endemic species. We link a population model with species distribution models to investigate expected changes in populations with climate change, the impact of altered fire regimes on population persistence and how much assisted colonization is necessary to minimize risk of decline in populations of Tecate cypress, a rare endemic tree in the California Floristic Province, a biodiversity hotspot. We show that assisted colonization may be a risk‐minimizing adaptation strategy when there are large source populations that are declining dramatically due to habitat contractions, multiple nearby sites predicted to contain suitable habitat, minimal natural dispersal, high rates of establishment of translocated populations and the absence of nonclimatic threats such as altered disturbance regimes. However, when serious ongoing threats exist, assisted colonization is ineffective.     

Climate change and amphibian declines: is there a link?

Abstract. Global climates have been changing, sometimes rapidly and dramatically, throughout the evolutionary history of amphibians. Therefore, existing amphibian species have been derived from those that have survived major climatic disturbances. Although recent global climate change has resulted in warming in many regions, temperatures in some areas to date have not changed measurably, or have even cooled. Declines of some amphibian populations have been correlated with climate events, but demonstrations of direct causal relationships need further research. Data are available indicating some indirect effect of climate change on the initiation of breeding activities of some amphibians that occur earlier than in previous springs, but the costs and benefits of these changes are just beginning to be investigated. Climate may also play an indirect role in facilitating epidemics of infectious disease. Regardless of the role that climate changes may have played in past and current amphibian declines, future shifts in climate, should they prove as dramatic as predicted, will certainly pose challenges for surviving amphibian populations and for successful recovery efforts of species that have suffered declines.     

Spatial and temporal variability of aquatic habitat use by amphibians in a hydrologically modified landscape

1. Habitat loss is a major driver of biodiversity decline worldwide. Temporary waterbodies are especially vulnerable because they are sensitive both to human impact and to climatic variations. Pond‐breeding amphibians are often dependent on temporary waterbodies for their reproduction, and hence are sensitive to loss of temporary ponds. 2. Here we present the results of a 5‐year study regarding the use of temporary aquatic habitats by amphibians in a hydrologically modified area of Eastern Europe (Romania). The annual number of aquatic habitats varied between 30 and ～120. Each aquatic habitat was characterised by a number of variables such as: ‘type’ (pond, drainage ditch and archaeological ditch), ‘hydroperiod’ (number of weeks the ponds were filled in a given year), ‘depth’ (cm), ‘area’ (m²) and the density of predatory insects (‘predation’). The turnover rate for each amphibian species for each wetland was calculated based on the pond occupancy. 3. Eight amphibian species were recorded from the aquatic habitats. Hydroperiod was the most important variable, positively influencing wetland use by amphibians and their reproductive success. Most species preferred drainage ditches for reproduction, and the reproductive success was highest in this habitat type every year. For most of the species, the local extinction rate was higher than the colonisation rate in the first 4 years, but the situation reversed in the last year of the study when wetland use by amphibians sharply increased because of high rainfall. 4. This study confirms the importance for amphibians of maintaining and managing aquatic habitat diversity at small spatial scales. Man‐made aquatic habitats such as drainage ditches may be important habitats for amphibians, and this should be considered in restoration activities.     

Six‐year demographic study reveals threat of stochastic extinction for remnant populations of a threatened amphibian

Sustained demographic studies are essential for early detection of species decline in time for effective management response. A paucity of such background data hindered the potential for successful conservation during the global amphibian decline and remains problematic today. The current study analysed 6 years of mark‐recapture data to determine the vital demographic rates in three habitat precincts of the threatened frog, Litoria aurea (Hylidae) and to understand the underlying causes of variability in population size. Variability in population size of L. aurea was similar to many pond‐breeding species; however this level of fluctuation is rare among threatened amphibians. Highly variable populations are at greater risk of local extinction and the low level of connectivity between L. aurea populations means they are at a greater risk of further decline due to stochastic extinction events and incapacity to recolonize distant habitat. We recommend that management of this species should encourage recolonization through creation of habitat corridors and reintroduction of L. aurea to areas where stochastic extinction events are suspected.     

Managed relocation as an adaptation strategy for mitigating climate change threats to the persistence of an endangered lizard

The distributional ranges of many species are contracting with habitat conversion and climate change. For vertebrates, informed strategies for translocations are an essential option for decisions about their conservation management. The pygmy bluetongue lizard, Tiliqua adelaidensis, is an endangered reptile with a highly restricted distribution, known from only a small number of natural grassland fragments in South Australia. Land‐use changes over the last century have converted perennial native grasslands into croplands, pastures and urban areas, causing substantial contraction of the species' range due to loss of essential habitat. Indeed, the species was thought to be extinct until its rediscovery in 1992. We develop coupled‐models that link habitat suitability with stochastic demographic processes to estimate extinction risk and to explore the efficacy of potential climate adaptation options. These coupled‐models offer improvements over simple bioclimatic envelope models for estimating the impacts of climate change on persistence probability. Applying this coupled‐model approach to T. adelaidensis, we show that: (i) climate‐driven changes will adversely impact the expected minimum abundance of populations and could cause extinction without management intervention, (ii) adding artificial burrows might enhance local population density, however, without targeted translocations this measure has a limited effect on extinction risk, (iii) managed relocations are critical for safeguarding lizard population persistence, as a sole or joint action and (iv) where to source and where to relocate animals in a program of translocations depends on the velocity, extent and nonlinearities in rates of climate‐induced habitat change. These results underscore the need to consider managed relocations as part of any multifaceted plan to compensate the effects of habitat loss or shifting environmental conditions on species with low dispersal capacity. More broadly, we provide the first step towards a more comprehensive framework for integrating extinction risk, managed relocations and climate change information into range‐wide conservation management.     

Synergies among extinction drivers under global change

If habitat destruction or overexploitation of populations is severe, species loss can occur directly and abruptly. Yet the final descent to extinction is often driven by synergistic processes (amplifying feedbacks) that can be disconnected from the original cause of decline. We review recent observational, experimental and meta-analytic work which together show that owing to interacting and self-reinforcing processes, estimates of extinction risk for most species are more severe than previously recognised. As such, conservation actions which only target single-threat drivers risk being inadequate because of the cascading effects caused by unmanaged synergies. Future work should focus on how climate change will interact with and accelerate ongoing threats to biodiversity, such as habitat degradation, overexploitation and invasive species.     

Global stressors and the global decline of amphibians: tipping the stress immunocompetency axis

There is a widespread consensus that the earth is experiencing a mass extinction event and at the forefront are amphibians, the most threatened of all vertebrate taxa. A recent assessment found that nearly one-third (32%, 1,856 species) of the world’s amphibian species are threatened. Amphibians have existed on the earth for over 300 million years, yet in just the last two decades there have been an alarming number of extinctions, nearly 168 species are believed to have gone extinct and at least 2,469 (43%) more have populations that are declining. Infectious diseases have been recognized as one major cause of worldwide amphibian population declines. This could be the result of the appearance of novel pathogens, or it could be that exposure to environmental stressors is increasing the susceptibility of amphibians to opportunistic pathogens. Here I review the potential effects of stressors on disease susceptibility in amphibians and relate this to disease emergence in human and other wildlife populations. I will present a series of case studies that illustrate the role of stress in disease outbreaks that have resulted in amphibian declines. First, I will examine how elevated sea-surface temperatures in the tropical Pacific since the mid-1970s have affected climate over much of the world and could be setting the stage for pathogen-mediated amphibian declines in many regions. Finally, I will discuss how the apparently rapid increase in the prevalence of amphibian limb deformities is linked to the synergistic effects of trematode infection and exposure to chemical contaminants.