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August 26, 2011 9:58 pm
While climatologists and politicians argue about the extent to which human activity is heating up the world, biologists charting the movements of plants and animals have no doubt that global warming is having a real impact on wildlife.
The most comprehensive study so far, published in the journal Science, shows that species have responded to climate change – by moving to higher latitudes and elevations where conditions are cooler – two to three times faster than scientists had appreciated.
The researchers, based at York University, analysed the response of 2,000 plant and animal species. They found that on average they have moved to higher altitudes by 12.2 metres per decade and to higher latitudes by 17.6 metres per decade.
“These changes are equivalent to animals and plants shifting away from the equator at around 20cm per hour, for every hour of the day, for every day of the year,” says Chris Thomas, professor of conservation biology at York.
Watching television for six hours a day shortens the viewer’s life expectancy by an average of almost five years, according to an Australian study published in the British Journal of Sports Medicine.
Many different factors are involved in wildlife population shifts. But this study is the first to prove that climate change is a key driver, by showing that species have moved furthest where conditions have warmed the most.
“We were able to calculate how far species might have been expected to move so that the temperatures they experience today are the same as the ones they used to experience, before global warming kicked in,” says Ralf Ohlemüller from Durham University. “Remarkably, species have on average moved towards the poles as rapidly as expected.”
Individual species show great variation in their movements, depending on other ecological factors and on their sensitivity to local aspects of climate change such as an increase or decrease in rainfall. In Britain, for instance, the distribution of the comma butterfly has raced 220km northward from central England to Edinburgh in two decades. Cetti’s warbler, a small bird, has moved 150km north since it began to colonise south-east England from continental Europe in the 1970s. But special factors have knocked a few species back in the opposite direction. The Cirl bunting retreated southward by 120km, probably in response to the intensification of UK agriculture.
The study was a “meta-analysis”, bringing together all known studies of the way species have changed their distribution in recent decades.
“Realisation of how fast species are moving because of climate change indicates that many species may be heading rapidly towards extinction,” Thomas says. “On the other hand, other species are moving to new areas where the climate has become suitable, so there will be some winners as well as many losers.”
Early wood: plumbing for plants
Scientists have pushed back the evolution of wood to the early Devonian period more than 400 million years ago. Their unexpected discovery seems to solve a mystery about the original purpose of wood.
A French-Belgian team report in the journal Science that the oldest known specimen of fossilised wood comes from a plant that grew in what is now France 407 million years ago. The second oldest is a Canadian specimen that dates from 397 million years ago.
The first woody plants are surprisingly small, with stems up to 5mm wide and 12cm long. The cellular structure is remarkably well preserved, with rings of cells – including elongated “ray” cells that are characteristic of wood – radiating outward from the centre.
Botanists have long debated two alternative theories about the evolutionary forces that led to wood. The traditional view is that it provided mechanical support – scaffolding to support plants as they grew taller, competing to harvest as much sunlight as possible.
But in the Science paper the scientists say their fossilised plants are too small to need wood for support. Instead they argue in favour of the alternative theory: that woody structures first developed for hydraulic purposes, as a plumbing system to help early plants draw water more efficiently into their cells.
A steep fall in levels of carbon dioxide in the atmosphere during the early Devonian period would have increased the need for efficient water transport, as plants had to work harder to convert CO2 and water into organic materials through photosynthesis.
Whatever the original trigger for woody stems, plants made use of the innovation relatively quickly to grow taller. By 385 million years ago some were the size of substantial shrubs and the first tree, archaeopteris, appeared 370 million years ago and quickly covered much of the Earth’s land with forests.
How the butterfly changed its spots
The astonishing ability of a single butterfly species to mimic several others now has a genetic explanation: a “supergene” enables the insect to morph into forms that look quite different though their DNA is almost identical.
Although many butterflies have evolved warning colouration that resembles another poisonous species to put off birds and other predators, Heliconius numata is remarkable because it can mimic not just one but several species – choosing whichever is most plentiful in its particular habitat.
An international team sequenced the DNA sequences responsible for wing patterns in H. numata, which is common in the Amazon rainforest. The scientists found that genes controlling different elements of the pattern were all clustered into a supergene on one chromosome. This enables DNA combinations that mimic other butterflies to arise quickly and then remain stable.
“We were blown away by what we found,” says Mathieu Joron of the Muséum National d’Histoire Naturelle in Paris, who led the research. “These butterflies are the ‘transformers’ of the insect world … A single genetic switch allows them to morph into several different mimetic forms – it is amazing and the stuff of science fiction.”
“By changing just one gene, the butterfly is able to fool its predators by mimicking a range of different butterflies that taste bad,” adds Richard ffrench-Constant of Exeter University, a co-author of the study published in Nature.
Shedding light on the darkest planet
Astronomers have discovered a distant planet that is much blacker than coal or the darkest paint you can buy.
TrES-2b, as it is known, is a Jupiter-sized planet orbiting a star about 750 light-years away.
Analysing TrES-2b with the Kepler space telescope, which was designed to study planets outside the solar system, known as exoplanets, US astronomers found that it reflects back less than 1 per cent of its parent star’s light. That is four times darker than the darkest known objects in the solar system.
TrES-2b is so close to its star that its surface temperature is above 1,000C. Its exotic atmosphere contains light-absorbing molecules such as sodium and potassium vapour and titanium oxide but these cannot explain fully its extreme blackness.
“It’s not clear what is responsible for making this planet so extraordinarily dark,” says David Spiegel of Princeton University. “However, it’s not completely pitch black. It’s so hot that it emits a faint red glow, much like a burning ember or the coils on an electric stove.”
After two years in orbit, Kepler has returned data on 1,200 exoplanet candidates. The next batch of data is due to be released next month.
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