Some species adapt to climate change, others face extinction
a number of recent studies have shown that climate change has a significant impact on various species, especially birds. While some show behavioural changes, some undergo genetic changes over a period of time, and others face the threat of extinction. With a heavy pressure on habitat and food source, there are examples showing that species tend to partially adapt themselves as well.
A study published in the October issue of Global Change Biology (Vol 12, No 10) showed that 78 per cent of all leafing, flowering and fruiting activities advanced by 30 per cent and only 3 per cent got delayed.
Climate change is leading to disruption in the food chain because of change in timings of plant growth or animal life cycles. The food web of the Bering Sea is among them. The walleye pollock (Theragra chalcogramma), a forage species, has declined due to variations in atmospheric circulation through interactions with ocean currents.
"Animals are finely tuned to seasons and often rely for food on the availability of different plant species throughout the year. If the timing of plant activity shifts, animals are left without a food source," says Elsa Cleland of the National Center for Ecological Analysis and Synthesis, us. She was part of the research on diverse responses of phenology (plant timings) to global warming and changes in grassland ecosystem.
According to estimates of the Audubon Society, a us-based conservation organisation, the population of the kittiwake, a seabird, is plunging because the fish they feed on have shifted location. In another instance, an off-season frost in Colorado is nipping life away from plants in many regions of the country, according to a University of Maryland paper published in Ecology Letters in October 2000. In the study, David Inouye, the lead author, found that the frost had led to a decline of squirrels by 17 per cent.
There are several other species which have been affected. Reduction in the area of sea ice formed near the Antarctic Peninsula has brought about a decline in the population of the krill, a key food source for predators like penguins, other sea birds, whales and seals. This is causing a heavy pressure on the diet of these animals. The Arctic tern no longer nests in Scotland because sand eel found in the North Sea on which the tern feeds, has been diminishing (see 'The seabirds have flown', Down To Earth, September 15, 2005). Polar bears, the largest extant land carnivores, have also suffered significantly. Climate change has caused lengthening of ice-free periods, during which the bears starve and live on their reserves because an ice shelf is necessary for feeding on ringed seal, the mainstay in their diet.
The reasons for such occurrences are obvious. "If climate change alters the timing of plant activity, then it could have a domino effect, impacting the feeding, breeding or migration patterns of the animals that rely on particular plant species," says Cleland. The disruptions in food chain are true for migrating animals. "A good example is the rufous hummingbird. It migrates from Mexico to Alaska and back each year, relying on plants with red blossoms that flower early in spring as they fly north along coastal routes. When they fly south in the fall they rely on late-flowering plants in the mountains. If species shift their flowering periods, these hummingbirds could be left without nectar during their long travels," adds Cleland.
In situations in which there is competition for food the difference in the levels of adaptability of various plants and animals leads to pressure on those that are less flexible, say scientists. "Species differ in their physiological tolerances, life-history strategies, probabilities of population extinction and colonisation, and dispersal abilities," says Camille Parmesan of the University of Texas who conducted a review of the responses of species to climate change recently.
There are many examples. Blackcap birds in central Europe have been increasingly wintering in Britain rather than Iberia. The genetically distinct British subpopulation arrives earlier at the nesting grounds and thus obtains superior territories or mates. These and several other case studies were compiled in a review paper published in the June 9 issue of Science (Vol 312, No 5779). The paper says that climate change has led to heritable genetic changes in populations of animals as diverse as birds, squirrels and mosquitoes.
The European butterfly, Aricia agestis, is a case in point. Scientists studied its adaptation to cool conditions by specialising on the host genus, helianthemum, which grows in hot microclimates and hence supports fast larval growth. Climate warming did not initially cause range expansion to the north because helianthemum was not available.
However, warming did permit rapid evolution of a broader diet at the southern range limit, depending on a different host, geranium, which grows in cooler microclimates. Once this local diet evolution occurred, the boundary also expanded northward, where geranium was present.
Fruit flies have also shown partial adaptation. Chromosomal inversions -- a difference in structure of the thread-like body that carries hereditary information -- that were present in fruit flies in latitudes closer to the equator decades earlier have now been observed further away from the equator.
"Though local evolutionary responses to climate change have occurred, there is no evidence of absolute adaptations of species to climate change. This results in weakening of certain species and extinction of many others that we have witnessed over the years," Parmesan says.
These changes are proof enough that there is a problem and the events to tackle climate change hardly indicate that the status quo will be broken.
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