. "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." In the Light of Evolution, Volume II: Biodiversity and Extinction. Washington, DC: The National Academies Press, 2008.
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In the Light of Evolution: Volume II—Biodiversity and Extinction
tial warming had already occurred since the early 1970s. Temperature increases were correlated with increases in the height at which clouds formed at Monteverde and consequent reductions in the deposition of mist and cloud water critical for maintenance of cloud forest conditions during the dry season (Pounds et al., 2006). Simulations using global climate models showed that greenhouse warming could have the effect of raising the cloud line by as much as 500 m at Monteverde during the dry season (Still et al., 1999; Pounds et al., 2006).
A more general effect of climate change has been proposed for the disappearance of 100 species of tropical montane frogs of the genus Atelopus, which is widespread in southern Central and northern South America. A detailed correlational analysis revealed that ≈80 species were last seen immediately after a warm year (Pounds et al., 2006). Several species disappeared from Ecuador during 1987–1988, which included the most extreme combination of dry and warm conditions in 90 years (Ron et al., 2003). Authors of that article document that the mean annual temperature in the Ecuadorian Andes has increased by ≈2°C during the last century.
Pounds and coworkers (2006) hypothesized that climate change, precipitation, and increased temperature have acted synergistically in favor of the growth of the infectious chytrid fungus. 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. Warming has increased cloud cover in these areas, which had the effect of elevating already higher nighttime temperatures, thus favoring fungal growth. The hypothesis has yet to be tested.
IS GLOBAL WARMING A REAL EXTINCTION THREAT?
The Intergovernmental Panel on Climate Change (IPCC) reached consensus that climate change is happening and that it is largely related to human activities (Parry et al., 2007). Estimates of global warming during the next century vary, but generally fall in the range of 2°C to 4°C, whereas rises as high as 7°C are projected for much of the United States and Europe, with even higher temperatures expected in northern Eurasia, Canada, and Alaska (Parry et al., 2007). Such rises would have devastating effects on narrowly distributed montane species, such as cloud forest and mountaintop salamanders and frogs in Middle and South America. The physiology of ectotherms such as amphibians and their ability to acclimate also are important considerations for these species (Calosi et al., 2008). With climate change (already 2°C changes in temperature have been recorded in montane Ecuador) (Ron et al., 2003), altitudinal limits of plant and animal