GLOBAL WARMING: The sheep are shrinking because of milder winters, a study says.The case of the shrinking sheep

The mysterious shrinking sheep of St Kilda sounds like a job for super-sleuth Sherlock Holmes. The case involves a rare herd of wild sheep on the remote Scottish island, known in Scottish Gaelic as Hirta, that are refusing to bow to conventional evolutionary pressure, which says big is best. Instead, they have steadily decreased in size since the 1980s.

Scientists have now stepped in to solve the conundrum, and fingered the culprit as the new Moriarty of mankind: global warming.

The experts say shorter and milder winters mean that lambs do not need to put as much weight on during their first few months of life. Smaller animals that would have perished in harsh winters a few decades ago can now survive to their first birthday. As a result, the average weight of the sheep has dropped by 81g each year.

The difference is too small to see with the naked eye, but it is important because it shows how animal populations can respond to climate change.

Biologists have reported that several species of birds and fish are changing size and shape, which could be down to global warming.

Coulson said it was difficult to say what the response of the St Kilda sheep could mean for other species. Their island home, St Kilda, is just “vegetation and sheep” he said. In other cases, predators and competition for food from other animals complicate the picture and make it difficult to tease out the influence of changing climate.

The study looked at a herd of wild Soay sheep on Hirta that biologists have studied since 1985. Dogs are forbidden on the island, so the scientists acted as human sheepdogs to herd the animals, which are expert jumpers, towards areas where they could be weighed. “These aren’t fluffy white sheep, these are small and brown and wild animals,” Coulson said.
The Guardian

Ecological impact of invasive species
The ecological effects of invasive species are often well known, particularly their impact on native plants or animals. But the invaders sometimes make love as well as war: they mate with related local species, producing hybrids. And the effects of such hybridisation have not been the subject of much study.

Now, research involving invasive and native salamanders in the Salinas Valley of California shows how devastating this can be: the hybrids have voracious appetites and can practically wipe out other species.

Maureen E Ryan and Jarrett R Johnson of the University of California, Davis, and Benjamin M Fitzpatrick of the University of Tennessee studied hybrids between native California tiger salamanders and barred tiger salamanders, brought in huge numbers from Texas beginning 60 years ago by California bait dealers. Tiger salamander larvae are high on a pond’s food chain, gulping down larvae of other species with their big mouths.

The researchers built artificial ponds, stocked them with salamanders and other species, notably the California newt and the Pacific chorus frog (both of which are found in the Salinas Valley) and monitored what happened. Their findings appear in The Proceedings of the National Academy of Sciences.

Hybrid larvae had a greater effect on the newts and frogs than native salamander larvae did, nearly wiping them out. Hybrids even affected the survival of native salamanders in the ponds.

“The implication is they are ecologically quite different from the native species,” Ryan said. That could spell trouble for other “third-party” species in the valley, like the California red-legged frog and the Santa Cruz long-toed salamander.
NYT News Service

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