Frogs feel the heat
Nature, April 2001
populations across the world have been in marked decline for several decades.
Various causes have been postulated for the fall, including disease, farm
chemicals and pollution.
Writing in this week's Nature, Kiesecker et al. present a study suggesting that climate change is the root cause of the creatures' demise. In particular, the study points a finger at recent powerful El Niño/Southern Oscillation cycles which strongly disrupt normal precipitation patterns in the Americas.
Because amphibians, such as the western toad Bufo boreas studied here, tend to spawn in shallow water, their embryos develop in direct sunlight and suffer from ultraviolet-B exposure. UV-B radiation is rapidly attenuated by water, so the damage done is highly dependent on water depth. El Niño events in particular, and global temperature rises in general, reduce the average water depth at spawning sites and hence increase UV-B exposure. The killer blow is dealt by the ubiquitous pathogenic fungus Saprolegnia ferax, which fatally infects the UV-B-weakened embryos.
The team found strong correlations linking El Niño/Southern Oscillation cycles, precipitation in the study area of Oregon's North Cascade Mountains, pond depth and amphibian mortality. In fact half of all embryos developing in water less than 20 cm deep failed to hatch due to S. ferax infection while those in 80 cm of water were barely affected.
In an accompanying News and Views article (below), Alan Pound sounds a note of caution, pointing out that species whose eggs are shielded from sunlight are also in decline, and that there are some doubts about the population surveys. Nevertheless he adds "If there is a link between the two [global warming and amphibian decline]&ldots; there is clearly a need for a rapid transition to cleaner energy sources if we are to avoid staggering losses of biodiversity."
J. Pounds. Climate and Amphibian Decline. Nature 410, 639-640 (5 April 2001)
Letter: Complex causes of amphibian population declines. Kiesecker, Blaustein & Belden. Nature 410, 681-684 (5 April 2001)
See the Nature site for more articles related to the worldwide amphibian decline.
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