February 28, 2011

More Good News for Frogs

Filed under: Adaptation, Animals

A couple of months ago we featured some recent scientific studies that showed that the future for frogs was apparently not going to be as bleak once projected—especially when it comes to the impacts of global warming.

Our article “A Frog Revival” was particularly popular, so we decided to highlighted some other fairly recent scientific papers that conclude that climate change is really not likely to be all that bad (and perhaps even pretty good) for various frog and other amphibian species.

The first such article appeared in the Proceedings of the National Academy of Sciences and carries the title “Decreased winter severity increases viability of a montane frog population.”

The article was produced by two scientists with the University of Montana and the work was financially supported by the US Geological Survey’s Amphibian Research and Monitoring Initiative. McCaffery and Maxwell begin their piece noting “Many proximate causes of global amphibian declines have been well documented, but the role that climate change has played and will play in this crisis remains ambiguous for many species.” Interesting start—they claim that the role of climate in declining frog numbers “remains ambiguous.” McCaffery and Maxwell further note “Breeding phenology and disease outbreaks have been associated with warming temperatures, but, to date, few studies have evaluated effects of climate change on individual vital rates and subsequent population dynamics of amphibians.” Hmmm, apparently the science seems far from settled on this issue.

McCaffery and Maxwell conducted a 9-year demographic study of Columbia spotted frogs in the Bitterroot Mountains of Montana; they collected data on local climate variables, frog survival and fecundity (fertility), and population growth rates. In their own words, these scientists report:

“These results unambiguously demonstrate that earlier ending winters with lower snowpack in this system lead to higher survival rates, higher probabilities of breeding, and higher population viability. Most research on amphibian declines assumes that climate change will have negative impacts on already vulnerable species, yet we show that this may not be the case for alpine and boreal amphibian populations currently persisting in harsh environments. This provides a unique perspective to the role of climate change in amphibian declines in temperate ecosystems.”

We highly doubt McCaffery and Maxwell made any friends in the climate change alarmist fraternity with that set of conclusions!

We found another pro-frog article in the journal Integrative Zoology written by three scientists with the University of Colorado; the work was funded by the National Science Foundation. Bustamante et al. begin by stating:

“Considerable controversy exists concerning whether or not climate changes (particularly global warming) are causing outbreaks of a lethal amphibian pathogen, the chytrid fungus Batrachochytrium dendrobatidis. In the present study, groups of Panamanian golden frogs a critically endangered amphibian thought to be nearly extinct in Panama, were exposed to varying dosages of zoospores of Batrachochytrium dendrobatidis, temperatures and hydric environments in order to learn whether this species is susceptible to this pathogen and, if so, how environmental factors affect survival.”

We can only imagine the amount of paperwork that went into this effort—conducting biological research on critically endangered species, transporting the Golden Frogs from the Maryland Zoo in Baltimore to a laboratory in Boulder, Colorado, and then conducting research that will cause death in some of the frogs? Good luck with that chore.

Bustamante et al. exposed the frogs to varying dosages of the zoospores, varying temperatures, and varying moisture conditions; 194 frogs participated in the study and they were treated to two to three week old crickets throughout their stay in Colorado. They conclude:

“Frogs exposed to a dosage of 100 Bd zoospores survived significantly (P < 0.0001) longer than those that had been exposed to 104 or 106 zoospores. Exposed frogs housed at 23°C survived significantly (P < 0.0001) longer than those that were housed at 17°C. Exposed frogs held in dry conditions survived significantly longer than those in wet conditions (P < 0.0001). As a laboratory study, these results do not directly test hypotheses about the relation between climate change and the decline of these frogs in the field, but they inform the discussion about how environmental conditions can have an impact on the interaction between a susceptible amphibian and this pathogen. These data do not support the contention that rising global temperatures are necessary to cause the death of amphibians infected with this pathogen because the pathogen was equally lethal at 17 as at 23°C, and frogs at the warmer temperature lived significantly longer than those at the cooler one.”

As these and many other scientific studies are documenting, you shouldn’t be quick to jump to the conclusion that climate change will be harmful to frogs. In fact, for some species at least, the impact may be quite the opposite!

References:

Bustamante, H.M., L.J. Livo, and C. Carey. 2010 Effects of temperature and hydric environment on survival of the Panamanian Golden Frog infected with a pathogenic chytrid fungus. Integrative Zoology, 5, 143-153.

McCaffery, R.M., and B.A. Maxell. 2010. Decreased winter severity increases viability of a montane frog population. Proceedings of the National Academy of Sciences, 107, 8644-8649.




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