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Amphibian decline in the Lamar Valley
By Tom Torma | January 12, 2009
The world’s amphibians are disappearing. It has been estimated that amphibians are going extinct at 211 times the normal background rate. The recent study “Climatic change and wetland desiccation cause amphibian decline in Yellowstone National Park” by Sarah K. McMenamin, Elizabeth A. Hadly, and Christopher K. Wright, suggests that Yellowstone is not immune from this world wide phenomenon.
The picture in Yellowstone is bleak. Of the four species studied, only the boreal toad has shown no serious decline, and that might be skewed because this species is already rare, meaning that there is a small sample size. The tiger salamander population has dropped by nearly half, while the spotted frog and chorus frog populations have dropped by 65% and 75% respectively.
The culprit appears to be climate change. The Yellowstone ecosystem has been getting dryer over the past half century, with 2001-2007 being the most severe drought on record. Most of decrease in precipitation has happened during the winter months, which has lead to a decrease in snow pack.
The study examined field comparisons of ponds in Lamar Valley between 1992-1993 and 2006-2008. Eight ponds that were permanent or ephemeral in the early study were found to be completely dry in 2006-2008, despite the fact that 2008 was the third wettest year on record. In addition, 11 additional ponds were dry in 2006-2007.
Of the remaining hydrated ponds, fewer are supporting amphibians. In the 1992-1993 survey, 43 of the 46 ponds supported amphibians, whereas in 2006-2008 only 21 of the 31 active, surveyed ponds supported amphibian life (there were 38 active ponds, but researchers were granted access to only 31). Indeed, even those 21 ponds were supporting fewer species, with no ponds hosting all four amphibian species.
Knock-on effects of climate change are probably also contributing to amphibian decline. Warming and drying in the park can lead to other factors, such as decreased leaf litter, that might affect how well a habitat supports a given species. In addition, rising temperatures can increase amphibian susceptibility to infectious disease. Whether this is happening in Yellowstone is not addressed in the study, but the authors point out that disease related die offs were only first observed in 2000, and outbreaks of chytridiomycosis and ranavirus have been observed in all four species.
The importance of this can not be overlooked. Aside from the virtue of saving these animals for their own sakes, amphibians are important food sources for a number of predators, such as herons, birds of prey, and coyotes. In addition, amphibians live and breathe in both the aqueous and atmospheric parts of our environment. As a result, they are susceptible to changes in the environment and are considered to be indicator species. Yellowstone is the one of the oldest, largest, and best preserved ecosystems in the world. The disappearance of amphibians from the Yellowstone ecosystem should act as an alarm call for us all.
Topics: Essays, General, Tom Torma |
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