Monday, 19 November 2012

Dwarfed Giants: Woolly Mammoths on Wrangel Island




Fig 1: Vartanyan et al (1993) Map of Wrangel Island

On the reading list for lecture 2 is an interesting (and conveniently, very short!) article by Vartanyan et al (1993) on Holocene dwarf mammoths on Wrangel Island, which survived long past the consensus extinction date of around 12,000 radiocarbon years BP of the ‘normal’ mammoth. Numerous sets of fossilized teeth 30% smaller than normal mammoth teeth have been found on Wrangel Island, and were dated as young as 7,000 – 4,000 radiocarbon years BP. Based on the relationship between tooth and body size, researchers have concluded that the dwarf mammoth was 180-230cm in shoulder height, at least 30% smaller than woolly mammoths on the mainland. 

Wrangel Island provided an isolated refugia for the mammoth in its dwarf form. In the late Pleistocene, Wrangel Island was part of the land of Beringida, joined up with the lowlands of East Siberia, Alaska and the present-day Arctic shelf. By 12,000 radiocarbon yeas BP, Wrangel Island was separated from the mainland, separating the local population of mammoth from the mainland population. This Arctic island had a much higher diversity of plant types and open vegetation, which supported mammoth populations. Even in the present day, the vegetation on this island is considered to be a poorer relic of late Pleistocene grassland.  Nevertheless, the dwarfing of mammoth size is an adaptation which reflected the severity of the stress that the original ‘normal’ mammoths faced in their original habitat. 


Fig 2: Stuart (2005) Timeline of Mammoth Extinctions in Different Regions

The significance of the Wrangel Island dwarf mammoths is that they provide a better understanding of how megafauna extinction took place, and the role of refugia. Extinction is not a one-off event in which animals are quickly wiped out, but rather, a gradual shrinking of range as these they increasingly found their environments unsuitable. Fig. 2 (above) illustrates the staggered extinction of mammoths, with some populations making their ‘last stands’ in certain places. A useful complementary article to read is Stuart’s(2005) more recent paper on new evidence of mammoths surviving much later than previously thought in other places that provided similar refugia, such as the new mammoth molars found in Estonia, which date to 10,000 radiocarbon years BP. Another example is the continued existence of woolly mammoth in the far north of Siberia, the Taymyr Peninsula, for another 2,000 radiocarbon years after most of them became extinct around the world. As the Holocene period brought warmer climates and forests rather than the open-steppe vegetation which favoured mammoths, such colder refugia allowed mammoths to survive. However, the Wrangel Island mammoths also add more mystery to the megafauna extinction debate. If climates became unsuitable, surely the mammoths were more vulnerable to change on an island, where migration was not possible, rather than on the mainland? Could it be the lack of humans on the island? Could human activities have inhibited the normal migrational responses of megafauna to climate change, thus limiting their range?

While the Wrangel Island mammoths raise even more questions on the megafauna debate than can be answered, it provides important lessons for modern conservation. Wrangel Island highlights the resilience and adaptability of natural ecosystems to change, e.g. through migration and physical adaptation (dwarfing). However, the combination of climate change and human impacts was just too much for the megafauna to bear. Today, as our ability to alter the environment is ever more profound, we need to be increasingly responsible for the consequences of our actions.

References

Vartanyan, S. L. (1993) ‘Holocene dwarf mammoths from Wrangel Island in the Siberian Arctic’, Nature 362, pp. 337-340.

Stuart, A. J. (2005) ‘The extinction of woolly mammoth (Mammuthus primigenius) and straight-tusked elephant (Palaeoloxodon antiquus) in Europe’, Quaternary International 126-128, pp. 171-177.

2 comments:

  1. Nice blog you have here, I've enjoyed reading your posts!

    Something interesting that I came across this article about mammoths on the Wrangel Island to do with the cause of the later extinction of these islanders. When thinking about population biology & islands, often time it would seem that a smaller population would in fact give rise to more inbreeding and lowered resilience, but apparently not for the mammoths on those islands- genetic diversity remained high all the way till extinction. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2012.05525.x/pdf

    Based on this, the authors rule out genetic reasons and point to environmental change- climate and/or humans- as the more probable cause for extinction of the islanders. It would be interesting to investigate the eventual cause of extinction for these last mammoths, given that a loss in genetic resilience is not likely the cause. Was it the eventual lost of 'refugia' conditions? Wonder if there is any information on this...

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  2. Hi Joy,

    Thanks! You raised an interesting point here that I did not think of - why the Wrangel Island mammoths eventually went extinct. A paper by Stuart et al (2004)
    http://www.nature.com/nature/journal/v431/n7009/full/nature02890.html
    points to either climate change or humans, which you rightly mentioned, although it also says that steppe-tundra vegetation (suitable mammoth habitat) remains on Wrangel Island to this day. There is also an interesting online article I found here:
    http://io9.com/5896262/the-last-mammoths-died-out-just-3600-years-agobut-they-should-have-survived
    which states that archaeological evidence suggests that there were humans arrived on Wrangel Island at around the same time the mammoths went extinct, but there is no evidence yet that they hunted the mammoths.
    While much mystery surrounds the cause of the final extinction of the Wrangel Island mammoths, the fact that genetic diversity remained high even within this small, isolated population offers good news for contemporary conservation - inbreeding is not an added threat for isolated pockets of highly endangered species.

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