Tuesday, 18 June 2013

Hot and Cold Running Lizards: Threatened by Climate Change or not?

The great majority of lizards prefer to live in places where daytime temperatures exceed 30 degrees Celsius. If you want to see a lot of lizards, or a great variety of species, head into the tropical and subtropical regions of the Earth. In the face of increasing global warming you wouldn't expect lizards to be especially vulnerable, right? As it so happens, opinions on the subject are mixed.

Back in 2009 a team of well-respected physiologists and herpetologists sounded an alarm: Global warming was coming fast, and with it many lizards would become extinct (University of Washington. "Tropical Lizards Can't Take The Heat Of Climate Warming."ScienceDaily, 5 Mar. 2009. Web. 18 Jun. 2013). That research team's leader was Raymond Huey, one of the intellectual powerhouses of reptile physiology. If Huey makes a claim in print, you'd better take it seriously.

But a few years later another team published a paper that presented the exact opposite case: in an ever-warming environment, most lizards would do better than they do now (Wiley. "Some like it hot: Cold-blooded tropical species 'not as vulnerable' to climate change extinction." ScienceDaily, 16 Aug. 2012. Web. 18 Jun. 2013.). The proposition that warmer climates will not threaten the majority of lizard species was supported by a separate study, also published in 2012 (Duke University. "Rapid changes in climate don't slow some lizards." ScienceDaily, 26 Nov. 2012. Web. 18 Jun. 2013.).

In March 2012 yet another study was published, this time supporting Huey's team and its conclusions (University of Lincoln. "Lizards facing mass extinction from climate change." ScienceDaily, 6 Mar. 2013. Web. 18 Jun. 2013.). That study's leader, , believes that warmer climates will drastically and negatively affect species that live at higher altitudes, especially those that produce live young instead of laying eggs. Then, on 17 May, another study concluded that climate change will barely affect lizards (Dartmouth College. "Climate change may have little impact on tropical lizards: Study contradicts predictions of widespread extinction."ScienceDaily, 17 May 2013. Web. 18 Jun. 2013).

This is how science is done. Scientists pick questions, seek answers, and often get conclusions that seem oppositional or totally unexpected. How, then, shall we choose which of several competing hypotheses to become our "truth"? We don't. Science is not democracy or hocus-pocus. We don't say something like, "well, three groups say that climate change will devastate lizards and two say they won't; let's go with the former." Scientists may come to consensus on many things, but should not do so on the basis of the number of published studies on a given topic. Too many studies provide excellent insight into a very tiny part of a question, but give us little or nothing from which to realistically extrapolate to, say, all organisms in a class.

In the studies mentioned above I see a few important limitations. Each study used only species from one genus (Anolis or Liolaemus). In the case of Anolis we have small species with short lifespans. Species with short lifespans tend to reproduce prodigiously, and in each generation may contain minute genetic modifications that could allow for greater thermal tolerance. Would the studies have gotten appreciably different results if a wider range of species been examined? Would size affect the results--say by comparing those tiny Anolis with 2m long iguanas?

The work being conducted is worthwhile, and is providing information that may become extremely important as the climate changes. However, I do not feel that the presentation of results based upon a very small sample of the species and environments concerned presents an accurate picture. Not all lizards might be so vulnerable, and maybe they are, but as of today there is no justification for claims that link any effect of climate change to the majority (or even a significant fraction) of the 4,500 species of living lizards.

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