Elsevier

Biological Conservation

Volume 125, Issue 3, October 2005, Pages 271-285
Biological Conservation

Review
The amphibian decline crisis: A watershed for conservation biology?

https://doi.org/10.1016/j.biocon.2005.04.009Get rights and content

Abstract

Amphibians have declined dramatically in many areas of the world. These declines seem to have worsened over the past 25 years and amphibians are now more threatened than either mammals or birds, though comparisons with other taxa are confounded by a shortage of reliable data. Research into amphibian declines has focused on: (1) documentation at the landscape or population level; and (2) observational and experimental work on potential causes of declines. Although loss of habitat is known to have impacted amphibians for decades, recent research has focused on the effects of environmental contaminants, UV-B irradiation, emerging diseases, the introduction of alien species, direct exploitation, and climate change. Such factors may interact with each other, but high levels of mortality do not necessarily lead to population declines. Major challenges remain in extrapolating from experimental data to population level effects, and in developing methodologies that will provide unbiased descriptions of amphibian population dynamics. Although amphibians have been widely advocated as good biological indicators, there is little evidence to suggest that they are more effective than other taxa as surrogate measures of biodiversity or habitat quality. As many of the threats facing amphibians are extremely difficult to neutralize in the short- to medium-term, the chances of ameliorating – let alone reversing – amphibian declines seem very poor.

Introduction

The discipline of conservation biology emerged specifically to understand, quantify and ameliorate the current biodiversity crisis (Soulé, 1986). Amphibians are playing an increasingly prominent role in this issue. The current era of research into amphibian declines followed the First World Congress of Herpetology in 1989 (Wake, 1991, Wake, 1998), though reports of declines go back at least 25 years before then (Pechmann and Wilbur, 1994). However, the Congress certainly precipitated an upsurge of interest as within a few years declines were reported for more than 500 amphibian species out of an estimated global total (at that time) of over 4000. A recent report from the IUCN’s Global Amphibian Assessment indicates that as many as a third of amphibian species, now estimated at over 5700, have undergone severe declines or extinction (Stuart et al., 2004) and that neotropical montane, stream-associated species are at particular risk. The declines have various likely causes, but there has been widespread controversy about their significance (Pechmann et al., 1991, Pechmann and Wilbur, 1994, Alford and Richards, 1999, Blaustein and Keisecker, 2002). In this review we: (1) briefly summarize research on causative factors (more comprehensive reviews on this aspect have been published elsewhere); (2) discuss the difficulties of extrapolation from experiments revealing possible causes of decline to demonstrating effects at the levels of populations and geographic ranges; and (3) consider how the study of amphibian declines relates to wider biodiversity issues, and the prospects for preventing continued amphibian declines. It is, however, important to be clear about how amphibian declines are defined (Green, 1997). In particular, we can identify declines in numbers of populations at the relatively large scale of biogeographic range, and fine-scale declines of specific populations in terms of overall size. Both are important but, as we shall see, the methods appropriate for investigating them can differ substantially.

Section snippets

Habitat destruction, agrochemicals and chemical pollution

Some reasons why amphibians decline have been understood for decades (Collins and Storfer, 2003). Temporal patterns of amphibian decreases reflect the major impact of habitat destruction in Europe during the mid-twentieth century, in contrast with more recent declines elsewhere (Houlahan et al., 2000). This conclusion has been contested, with the suggestion that global declines only began in the 1990s (Alford et al., 2001), but intensive arable farming starting in the mid-20th century has

Measuring effects at the distributional level

The overall significance of amphibian declines is manifest at the geographical range scale. Determining trends across a range requires an estimation of numbers of occupied sites at the landscape level (Green, 1997), usually with substantial resource implications due to the amount of effort involved. It is nevertheless essential because instability – or even declines – of local populations may not be reflected in overall changes at larger geographic scales. Green frog R. clamitans populations,

Amphibians and the wider biodiversity crisis

Within the context of the wider biodiversity crisis, two fundamental questions about amphibian declines arise: (1) Are amphibians particularly good indicators of a wider biodiversity malaise? (2) Are amphibians declining faster than other taxa? Since 1989 amphibians have been widely advocated as excellent ‘biological indicators’ or sensitive indicators of environmental health (e.g., Blaustein and Wake, 1990, Vitt et al., 1990, Wyman, 1990, Wake, 1991). These claims have been reiterated in more

Conclusions

What, then, should be the priorities for research into the amphibian decline phenomenon? In a thought-provoking essay, Caughley (1994) opined that conservation biologists would be unable to realise their goals of saving species from extinction unless empirical case studies of declining populations were underpinned by more theory. He argued that conservation biology is therefore progressing in two directions – enshrined within the ‘declining population paradigm’ and the ‘small population

Acknowledgements

We thank the many research students and fellows who have worked in our laboratories over past years, and English Nature, The Leverhulme Trust, The Darwin Initiative and the Natural Environment Research Council for financial support. We are also grateful to B. Schmidt, J. Gerlach and an anonymous review for constructive criticism of an earlier manuscript.

References (147)

  • M.A. Alexander et al.

    Climate variability in regions of amphibian declines

    Conservation Biology

    (2001)
  • R.A. Alford et al.

    Global amphibian declines: a problem in applied ecology

    Annual Review of Ecology and Systematics

    (1999)
  • R.A. Alford et al.

    Global amphibian population declines

    Nature

    (2001)
  • J.W. Arntzen et al.

    Italian crested newts (Triturus carnifex) in the basin of Geneva: distribution and genetic interactions with autochthonous species

    Herpetologica

    (1999)
  • J.D. Austin et al.

    Controlling for the effects of history and non-equilibrium conditions in gene flow estimates in northern bullfrog (Rana catesbeiana) populations

    Genetics

    (2004)
  • T.J.C. Beebee

    Amphibian decline?

    Nature

    (1992)
  • T.J.C. Beebee

    Amphibian breeding and climate

    Nature

    (1995)
  • T.J.C. Beebee et al.

    Application of genetic bottleneck testing to the investigation of amphibian declines: a case study with natterjack toads

    Conservation Biology

    (2001)
  • L. Berger et al.

    Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America

    Proceedings of the National Academy of Sciences USA

    (1998)
  • K.A. Berven et al.

    Dispersal in the wood frog (Rana sylvatica): implications for genetic population structure

    Evolution

    (1990)
  • R. Biek et al.

    What is missing in amphibian decline research: insights from ecological sensitivity analysis

    Conservation Biology

    (2002)
  • A.R. Blaustein et al.

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

    Ecology Letters

    (2002)
  • A.R. Blaustein et al.

    Amphibian declines: judging stability, persistence, and susceptibility of populations to local and global extinctions

    Conservation Biology

    (1994)
  • A.R. Blaustein et al.

    Ultraviolet radiation, toxic chemicals and amphibian population declines

    Diversity and Distributions

    (2003)
  • A.R. Blaustein et al.

    Amphibian breeding and climate change

    Conservation Biology

    (2001)
  • A.R. Blaustein et al.

    UV repair and resistance to solar UV-B in amphibian eggs; A link to population declines?

    Proceedings of the National Academy of Sciences USA

    (1994)
  • E.G. Brede et al.

    Contrasting population structure in two sympatric anurans: implications for species conservation

    Heredity

    (2004)
  • A.S. Bridges et al.

    Temporal variation in anuran calling behaviour: implications for surveys and monitoring programs

    Copeia

    (2000)
  • J. Buckley et al.

    Monitoring the conservation status of an endangered amphibian: the natterjack toad Bufo calamita in Britain

    Animal Conservation

    (2004)
  • T.M. Caro et al.

    On the use of surrogate species in conservation biology

    Conservation Biology

    (1999)
  • C. Carey et al.

    Climate change and amphibian declines: is there a link?

    Diversity and Distributions

    (2003)
  • G. Caughley

    Directions in conservation biology

    Journal of Animal Ecology

    (1994)
  • J.P. Collins et al.

    Global amphibian declines: sorting the hypotheses

    Diversity and Distributions

    (2003)
  • J.P. Collins et al.

    A model host–pathogen system for studying infectious disease dynamics in amphibians: tiger salamanders (Ambystoma tigrinum) and Ambystoma tigrinum virus

    Herpetological Journal

    (2004)
  • A.S. Cooke

    A comparison of survey methods for crested newts (Triturus cristatus) and night counts at a secure site, 1983–1993

    Herpetological Journal

    (1995)
  • B.R. Coppedge et al.

    Avian response to landscape change in fragmented southern Great Plains grasslands

    Ecological Applications

    (2001)
  • J.M. Cornuet et al.

    Description and power analysis of two tests for detecting recent population bottlenecks from allele frequency data

    Genetics

    (1996)
  • W.B. Crouch et al.

    Using egg-mass counts to monitor wood frog populations

    Wildlife Society Bulletin

    (2000)
  • W.B. Crouch et al.

    Assessing the use of call surveys to monitor breeding anurans in Rhode Island

    Journal of Herpetology

    (2002)
  • C.P. Cummins

    Testing for the effects of UV-B radiation on anti-predator behavior in amphibians: a critique and some suggestions

    Ethology

    (2002)
  • A.A. Cunningham et al.

    Pathological and microbiological findings from incidents of unusual mortality of the common frog (Rana temporaria)

    Philosophical Transactions of the Royal Society of London B

    (1996)
  • P. Daszak et al.

    Infectious disease and amphibian population declines

    Diversity and Distributions

    (2003)
  • P. Daszak et al.

    Experimental evidence that the bullfrog (Rana catesbeiana) is a potential carrier of chytridomycosis, an emerging fungal disease of amphibians

    Herpetological Journal

    (2004)
  • C. Davidson

    Declining downwind: amphibian population declines in California and historical pesticide use

    Ecological Applications

    (2004)
  • C. Davidson et al.

    Decline of the California redlegged frog: climate, UV-B, habitat and pesticide hypotheses

    Ecological Applications

    (2001)
  • C. Davidson et al.

    Spatial tests of the pesticide drift, habitat destruction, UV-B, and climate change hypotheses for California amphibian declines

    Conservation Biology

    (2002)
  • J.S. Denton et al.

    Reproductive strategies in a female-biased population of natterjack toads (Bufo calamita)

    Animal Behaviour

    (1993)
  • J.S. Denton et al.

    A recovery program for the natterjack toad (Bufo calamita) in Britain

    Conservation Biology

    (1997)
  • S. Esteal et al.

    The ecological genetics of introduced populations of the giant toad, Bufo marinus (Amphibia: Anura): dispersal and neighbourhood size

    Biological Journal of the Linnean Society

    (1986)
  • C.S. Findlay et al.

    Response time of wetland biodiversity to road construction on adjacent lands

    Conservation Biology

    (2000)
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