November 16, 2009

Did Climate Change Lead To Giant Deer Extinction?

New research suggests that the giant deer, also known as the giant Irish deer or Irish elk, one of the largest deer species that ever lived, likely died off because of climate change, BBC News reported.

The giant deer (Megaloceros giganteus), which had massive antlers, suddenly went extinct some 10,600 years ago and a new study of its teeth suggests that as conditions became colder and drier in Ireland at the time, fewer plants grew, gradually starving the deer.

Initial ideas for why the giant deer went extinct ranged from the biblical flood described in Genesis, to the idea that humans had wiped them out.

However, the archaeological record suggests that people did not arrive in Ireland until after the last Ice Age, after most giant deer had disappeared and there is little evidence that the deer had any predators in Ireland.

Some experts even suggested that the deer's huge antlers, spanning up to 12 feet, grew disproportionately large due to sexual selection.

According to that theory, the females became attracted to and mated with males with ever-larger antlers and eventually the antlers became so unwieldy that the deer became mired in clay soils, where they perished.

Kendra Chritz, who conducted the study at the University College (UCD), Dublin, Ireland and the National Museum of Ireland, believes that explanation is too simplistic for why such a massive population of apparently thriving organisms could go extinct suddenly.

Chritz and colleagues analyzed the tooth enamel of seven fossilized male giant deer and showed that by studying levels of carbon and oxygen isotopes, and levels of cementum, a material that cements each tooth crown to the gums, the researchers could uncover the time of year each deer was born, their diet and how their lives and behavior may have changed over time.

The study showed that the ratios of isotopes revealed that the ecosystem in which the deer lived became stressed by drought, resulting in a change from being covered in forest to being more open and tundra-like.

Chritz called it an overall trend of general vegetation decline.

She said the giant deer would probably have had a hard time coping with cooler mean annual temperature and a shortened growing season.

Considering that most young animals are born in spring precisely because temperatures are warmer and there is more food available, such conditions would be particularly bad news for young deer.

Chritz, who is now studying for her PhD in palaeoecology at the University of Utah in Salt Lake City, said it would be very difficult for young deer to cope with all these changes brought on by the Ice Age, as well as support the energetic demands of their growing bodies.

Cementum data indicates that the deer lived from 6.5 to 14 years old, and they possessed mature antlers by autumn, similar to other living deer species.

Megaloceros giganteus is actually a deer species, despite often being called the Irish elk. Populations had even spread across Europe and Western Asia from 400,000 to 10,600 years ago.

However, during the last Ice Age, the deer rapidly disappeared across most of the range at the end of the last glacial transition, though giant deer remains have been uncovered in Siberia that date to around 7,000 years before present.

"That means that mainland giant deer had some sort of refugia from the Ice Age before they met their ultimate extinction; they were able to move to a better environment and survive later," said Chritz.

But those giant deer in Ireland had the misfortune to be trapped on an island with nowhere to go, she said.

The full study was published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.


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