In the Light of Evolution Volume II: Biodiversity and Extinction (2008) / Chapter Skim
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2 Are We in the Midst of the Sixth Mass Extinction? A View from the World of Amphibians--DAVID B. WAKE and VANCE T. VREDENBURG
2 Are We in the Midst of the Sixth Mass Extinction? A View from the World of Amphibians--DAVID B. WAKE and VANCE T. VREDENBURG
Pages 27-44
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From page 27... ...
A new and significant threat to amphibians is a virulent, emerging infectious disease, chytridiomycosis, which appears to be globally distrib uted, and its effects may be exacerbated by global warming. This disease, which is caused by a fungal pathogen and implicated in serious declines and extinctions of >200 species of amphibians, poses the greatest threat to biodiversity of any known disease.
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From page 28... ...
We begin with a general overview of past mass extinctions to determine where we now stand in a relative sense. Our specific focus, however, is a taxon, the Class Amphibia.
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From page 29... ...
was associated with the opening of the Atlantic Ocean by sea floor spreading related to massive lava floods that caused significant global warming. Marine organisms were most strongly affected (22% of marine families and 53% of marine genera were lost)
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From page 30... ...
A large number of factors have been implicated, including most prominently habitat destruction and epidemics of infectious disease (Pechmann and Wake, 2006) ; global warming also has been invoked as a contributing factor (Pounds et al., 2006)
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From page 31... ...
Such species may have little acclimation ability in rapidly changing thermal regimes. In general, amphibians have small geographic ranges, but this is accentuated in most terrestrial species (the majority of salamanders; a large proportion of frog species also fit this category)
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From page 32... ...
(Inset) Baseline world map.
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From page 33... ...
The mountain range spans thousands of square kilometers of roadless habitat, most of which is designated as National Park and Forest Service Wilderness Areas, the most highly protected status allowable under U.S.
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From page 34... ...
Baseline world map. Visualization based on densityequalizing cartograms prepared by M
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From page 35... ...
Although most of the frog habitat in this large mountain range is protected in national parks and wilderness areas, yellow-legged frogs are now documented to have disappeared from >90% of their historic range during the last several decades (Vredenburg et al., 2007)
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From page 36... ...
. Mitochondrial DNA sequence data identified six geographically distinct haplotype clades in the two species of frogs, and we recommended that these clades be used to define conservation goals.
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From page 37... ...
. Particularly striking about this case is the highly protected status of the preserve, so habitat destruction, the most common reason for species disappearances in general, can be excluded.
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From page 38... ...
Vredenburg were enigmatic, but eventually two primary causal factors emerged: the infectious disease chytridiomycosis and global warming (Lips et al., 2006; Pounds et al., 2006)
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From page 39... ...
They argue that global warming has shifted temperatures closer to the presumed optimal conditions for B dendrobatidis at Monteverde and the other intermediate elevation areas of the Central and South American highlands, where most of the extinctions of Atelopus have occurred.
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From page 40... ...
The section of the Sierra Madre Oriental we have been studying is home to 17 named and 3–5 as yet unnamed species of the plethodontid salamander genus Thorius, the minute salamanders. All but four of these species occur exclusively at >2,000 m, often on mountains that rise only
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From page 41... ...
The range extends in a generally north-northeast to south-southwest direction, but the section from Cofre de Perote to Loma Alta extends mainly east-northeast and has been straightened. This mountain system is home to 17 described and several unnamed species of minute salamanders, genus Thorius.
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From page 42... ...
Vredenburg are especially susceptible to other stressors, such as introduced species and disease. Tropical montane species are at special risk because of global warming.
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From page 43... ...
Koo. zpq9990837760005.c.eps will survive the current extinction event on salamanders, and caecilians their own or with help, even as their ancestors survived the four preced ing mass extinctions.
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From page 44... ...
showed that many factors are contributing to the global extinctions and declines of amphibians in addition to disease. Extrinsic forces, such as global warming and increased climatic variability, are increasing the susceptibility of high-risk species (those with small geographic ranges, low fecundity, and specialized habitats)
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