December 20, 2010

Understanding How Science Works

Non-scientists are often understandably frustrated by the conflicting results commonly reported in the media on any one of a myriad of science-related topics. It seems that hardly a day goes by that we don't hear another story about how a previous study showed one thing but the newest study now refutes those results. With all of this conflicting information I can understand when some people throw up their hands and conclude that scientists don't know what the heck they are talking about.

This lack of clarity can be partly attributed to the superficial coverage provided by most media outlets in this sound-bite age of ours. When a relatively complex issue is distilled down to a one minute story there are bound to be lots of important facts lost in the process. However, to a large extent these conflicting results are inherent in how science works. Scientific progress is not a linear path. Instead, it is a process that zigs and zags and over time closes in on something resembling the truth. This non-linear progression may be frustrating but it is an unavoidable consequence of the fact that complex questions have complex answers (and are there any simple questions these days?) and different approaches to these questions will often provide different answers.  

The amphibian decline literature provides some excellent examples of this non-linear scientific progression. For example, starting in the mid-1990s Andrew Blaustein at Oregon State University published a series of papers in high-profile scientific journals showing that ultraviolet (UV) radiation had a range of negative effects on amphibians and that increasing UV radiation could be responsible for global amphibian declines.This hypothesis was compelling because it fit with known increases in UV radiation resulting from thinning of the ozone layer and it potentially explained the global nature of these declines. As a consequence, the UV hypothesis received lots of attention from the media and these many stories had the effect of solidifying in the public's mind that UV radiation was in fact a cause of amphibian declines. In fact, the science to test that hypothesis in different ecosystems and using different methods had just begun.

As with any novel idea Blaustein's hypothesis caught the attention of other scientists and in the following 15 years resulted in a plethora of additional scientific studies focused specifically on testing the idea. That research has provided a much more comprehensive picture of the effects of UV radiation on amphibians. In large part, the current thinking is generally that global UV radiation levels have in fact increased during the last 30 years but these increases have been relatively modest (~5% in North America) and have leveled off since the mid-1990s. For several reasons these increases, although obviously of concern, don't necessarily translate into impacts to amphibians. First, UV radiation has been a selective force on amphibians since amphibians first evolved more than 300 million years ago. As a consequence many amphibians have adaptations that effectively protect them from UV exposure. Second, water is a strong attenuator of UV radiation and can block UV from even reaching amphibian life stages. So, increased UV radiation may be having some effects in localized areas but this hypothesis is no longer seen as providing a general explanation for global amphibian declines. 

So, science worked the way it almost always does: someone puts out an idea and then over subsequent years that idea is subjected to many tests by different groups of people and we eventually arrive at a more complete understanding of the phenomenon in question. To understand the full story you just need to read beyond the splashy headlines.

For more information on UV radiation and its impacts on amphibians check out the following papers (you can find PDFs of most of these by conducting your searches using Google Scholar):

Adams, M. J., B. R. Hossack, R. A. Knapp, P. S. Corn, S. A. Diamond, P. C. Trenham, and D. B. Fagre. 2005. Distribution patterns of lentic-breeding amphibians in relation to ultraviolet radiation exposure in western North America. Ecosystems 8:488-500.

Blaustein, A. R., P. D. Hoffman, D. G. Hokit, J. M. Kiesecker, S. C. Walls, and J. B. Hays. 1994. UV repair and resistance to solar UV-B in amphibian eggs:  a link to population declines? Proceedings of the National Academy of Sciences, USA 91:1791-1795.

Blaustein, A. R. and D. B. Wake. 1995. The puzzle of declining amphibian populations. Scientific American 272:52-57.

Herman, J. R. 2010. Global increase in UV irradiance during the past 30 years (1979–2008) estimated from satellite data. Journal of Geophysical Research 115: D04203.

Kiesecker, J. M., A. R. Blaustein, and L. K. Belden. 2001. Complex causes of amphibian population declines. Nature 410:681-684.

Palen, W. J. and D. E. Schindler. 2010. Water clarity, maternal behavior, and physiology combine to eliminate UV radiation risk to amphibians in a montane landscape. Proceedings of the National Academy of Sciences 107:9701-9706.

Vredenburg, V. T., J. M. Romansic, L. M. Chan, and T. Tunstall. 2010. Does UV-B radiation affect embryos of three high elevation amphibian species in California? Copeia 2010:502-512.

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December 14, 2010

Frog Recovery - An Emerging Story

I've spent a large portion of the last 10 years describing the spread of the amphibian chytrid fungus (Batrachochytrium dendrobatidis - "Bd") across the Sierra Nevada. Given the hundreds of frog population extinctions that have resulted from the arrival of Bd it is sometimes easy to forget about the other side of this story - that there is also evidence of frog recovery following Bd-caused population crashes. 

To read more about what is happening in the Sierra Nevada and Australia check out this recent story in the New Scientist. The writer somewhat exaggerates the recovery angle but it is a worthwhile read nonetheless. The reality in the Sierra Nevada is that recovery of populations to a pre-Bd population size is very rare and has happened at just a handful of sites. But the fact that it is happening at all is important.

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