Climate link to amphibian decline

Amphibian populations at Yellowstone - the world's oldest national park - are in steep decline, a major study shows.

The authors link this to the drying out of wetlands where the animals live and breed, which is in turn being driven by long-term climate change.

The results, reported in the journal PNAS, suggest that climate warming has already disrupted one of the best-protected ecosystems on Earth.

The park covers some 9,000 sq km (3,500 sq miles) in the western United States.

It lies mostly within the state of Wyoming, but spills over into Montana and Idaho. The area has been protected for more than a century; US congress granted Yellowstone national park status on 1 March 1872.

'There is a pretty substantial signal of climate change in this region.'
Sarah McMenamin, Stanford University

Visitors flock there to see its geysers, hot springs and bubbling mud pots, fuelled by ongoing volcanism. The park's vast forests and grasslands are also home to grizzly bears, wolves and bison.

But it is to much less conspicuous inhabitants - frogs, toads and salamanders - that scientists look for early indications of environment degradation.

Four amphibian species are native to the park: the blotched tiger salamander (Ambystoma tigrinum melanostictum), the boreal chorus frog (Pseudacris triseriata maculata), the Columbia spotted frog (Rana luteiventris) and the boreal toad (Bufo boreas boreas).

The lower Lamar Valley in northern Yellowstone harbours countless small, fishless ponds - ideal for amphibian breeding and larval development.

Downward trend

Between 1992 and 1993, researchers surveyed 46 of these "kettle" ponds, which are re-filled in spring by groundwater and snow melt running down from the hills.

The "kettle" ponds are ideal habitats for amphibians. When a team from Stanford University in California repeated this survey between 2006 and 2008, the number of permanently dry ponds had increased four-fold.

Of the ponds that remained, the proportion supporting amphibians had declined significantly.

In addition, three of the four native amphibian species had suffered major declines in numbers. The number of species found in each location - the "species richness" - had also dropped off markedly.