Salamanders Declining in Latin America

My research on amphibian declines focuses almost exclusively on mountain yellow-legged frogs. As such, it is easy to forget the fact that the amphibian decline phenomenon has a global reach and that these declines affect a huge diversity of amphibian species. Compared to the large body of evidence showing declines in frogs and toads, evidence for salamander declines has been sparse but a new paper in the Proceedings of the National Academy of Sciences (available here) brings these declines into startling focus. Rovito et al. describe the disappearance of multiple salamander species from montane sites in Mexico and Guatemala (figure from paper showing these declines is shown to left). Surveys conducted at the study sites in the 1970s turned up more than 70 salamanders per visit but surveys in 2005-2007 at the same sites turned up fewer than five salamanders per visit. Several of the most common species during the 1970s were not found during any of the recent surveys and may be extinct.

Given the very high diversity of salamanders in the Neotropics these declines suggest that many salamander species may be at much higher risk of extinction than has been appreciated. Unfortunately the cause of the declines described by Rovito et al. remains obscure. The amphibian chytrid fungus was detected on some salamanders at the study sites and could be a contributing factor as could climate change.

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More About Climate Change and Amphibian Declines

The role of climate change as a driver of amphibian declines is a controversial topic. As I described in my 3/27/2008 post, an article by Pounds et al. in Nature suggested that climate warming in South America was responsible for the emergence of the amphibian chytrid fungus (Batrachochytrium dendrobatidis) and subsequent catastrophic amphibian declines on that continent. These results have been challenged on several grounds, and in my view remain conjectural at best.

An article just published in the Proceedings of the National Academy of Sciences provides much clearer evidence that recent climatic anomalies have resulted in declines of amphibian populations. The authors report that six decades of climate data for Yellowstone National Park shows a trend of increasing temperatures and decreasing precipitation. These changes in temperature and precipitation have caused many of the ponds in the study area to dry up. This, in turn, has resulted in marked decreases in the number of sites occupied by three species of amphibians: blotched tiger salamander (Ambystoma tigrinum melanostictum), boreal chorus frog (Pseudacris triseriata maculata), and Colombia spotted frog (Rana luteiventris). These results are certainly of concern, but it remains to be seen whether these patterns hold up over the longer term.

Direct effects of climate change on amphibians due to consequent changes in habitat are likely to increase in severity in coming decades. Even the mountain yellow-legged frog, a species that requires permanent water bodies for successful breeding and overwintering, will likely be affected as what were once permanent lakes, ponds, and streams become ephemeral. Such changes could spell extinction for many populations of this already imperiled species.

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Climate Change and Global Amphibian Declines

In 2006, Alan Pounds and colleagues published a paper in the journal, Nature, that claimed to show a link between global warming and the worldwide decline of amphibians. They argued that warming temperatures had allowed the emergence of chytridiomycosis, a disease caused by the amphibian chytrid fungus that has been wiping out amphibian species around the world. Despite providing only weak support for the role of climate change, the paper was splashed across the pages of hundreds of newspapers and magazines, all repeating the mantra that climate change was now a proven cause of amphibian declines.

This week, Karen Lips and colleagues published a paper in the journal, PLoS Biology, that challenges the conclusions of the Pounds paper. Although the media has portrayed the new paper as debunking the link between climate change and amphibian declines, the Lips et al. paper actually only refutes the analyses that Pounds et al. conducted and used to make their claim of a strong link between climate change and amphibian declines. This is an important distinction but one that as usual, is lost in the rush to create a catchy headline.

Both studies used similar data sets that describe the timing of amphibian declines in South America during the past several decades. However, the new paper reports that the link to climate change trumpeted by Pounds et al. is weakly supported at best. Lips et al. suggest that a more parsimonious explanation of the patterns of amphibian decline in South America is multiple introductions of the amphibian chytrid fungus into South America and subsequent spread across the continent. Lips et al. contend that there is no evidence for climate change driving this spread.

None of this detracts from the very real challenges posed by climate change to the conservation of amphibians around the world. It just highlights the important point that there is currently little support for the idea that global warming is responsible for amphibian declines.

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Conservation in an Age of Climate Change

The February 4, 2008 issue of High Country News featured a cover story entitled, "Unnatural Preservation", by Martin Smith and Fiona Gow. In this article, Smith and Gow ponder a question that managers and scientists increasingly face while trying to do their jobs in a warming world: "Do we rush to rescue climate-imperiled species before it's too late? Or do we let nature take its course, quietly watching the disappearance of species that we have spent decades restoring and protecting?" There is no doubt that global warming will in coming decades, profoundly reshape the Earth's ecosystems, but can we really manage these changes? Do we move species to higher elevations and latitudes as their historic habitat becomes too warm? Do we remove "nonnative" species that colonize national parks and wilderness areas as a consequence of warming temperatures? Do we water ecosystems in response to the drying conditions that will accompany climate warming in many regions of the world?

There are several reasons that humans cannot play the role of "gardeners and zookeepers" as envisioned by Smith and Gow. First, the magnitude of the problem is far beyond our ability to manage. The Earth contains tens of millions of species, most that remain undescribed. These species and their ecosystems are excruciatingly complex, and this complexity will for the foreseeable future remain well outside of the realm of human comprehension. To pretend that we can manage the Earth's diversity and ecosystems to mitigate effects of global warming is delusional. Second, the gardener and zookeeper approach would by necessity focus on the most obvious ecosystem components, charismatic fauna and flora such as grizzly bears and giant sequoias, condors and saguaros. Managing even these relatively few and well-studied taxa would be an immense undertaking and this targeted approach would completely ignore the myriad other, less conspicuous taxa that often are at least as important as the charismatic species in determining ecosystem structure and function. And third, playing the role of the Earth's gardener and zookeeper requires understanding how ecosystems function, and to be blunt, we haven't a clue. A well-informed ecologist might be able to provide a rough sketch of how a corn field functions, but when it comes to natural, complex ecosystems, forget it. Even our best attempts to manage this diversity would do far more harm than good.

Our best hope of mitigating the effects of climate change is not frantic, poorly-informed attempts to manage the consequences, but instead to deal seriously and immediately with the driver of global warming: the build-up of carbon dioxide and other greenhouse gases in the Earth's atmosphere. Despite the enormity of that task, it pales in comparison to what would be required to manage the Earth's fauna and flora to mitigate the effects of climate change. No matter how effective the response of human societies is to rising greenhouse gas emissions, global warming will accelerate for decades to come. As these resulting changes to the Earth's ecosystems unfold, we'll have little choice but to watch.

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