Author: By Steve Connor, Science Editor
Insects in the tropics are already living at the limit of their temperature range and any further increases could quickly kill them off with huge repercussions for tropical habitats, which rely on insects for everything from pollination to waste disposal. Scientists have found that a rise in average temperatures in the tropics of just 1C or 2C could be enough to exert a significant and harmful effect on the survival of a wide variety of important insects.
Climate scientists predict that the polar regions will experience the greatest increases in average temperatures this century as a result of climate change, but the latest study suggests that even the smaller predicted change in the tropics could have a far more serious impact on local wildlife.
“Many tropical species can only tolerate a narrow range of temperatures because the climate they experience is pretty constant throughout the year,” said Curtis Deutsch, assistant professor of atmospheric and oceanic sciences at the University of California, Los Angeles, who co-authored the study published in the journal Proceedings of the National Academy of Sciences. “Our calculations show that they will be harmed by rising temperatures more than would species in cold climates. Unfortunately, the tropics also hold the large majority of species on the planet.”
Insects are critical to the health of tropical habitats because they perform vital services such as breaking down organic matter, pollinating flowers to produce fruits and nuts and providing sustenance for creatures higher up the food chain. However, the scientists found that tropical insects live in a narrow range of temperatures and anything outside this range, especially at the higher end, could easily kill them off because they have no way of adapting or moving.
“There’s a strong relationship between your physiology and the climate you live in. In the tropics many species appear to be living at or near their thermal optimum, a temperature that lets them thrive,” said Joshua Tewksbury, of Washington University, another of the study’s co-authors. “But once temperature gets above the thermal optimum, fitness levels most likely decline quickly and there may not be much they can do about it.”
The scientists used daily and monthly global temperatures from between 1950 and 2000 and compared them against a raft of data indicating overall species “fitness”, as determined by indicators such as population growth rates and physical performance for different creatures.
They found that even a slight increase in temperature had a negative effect on fitness because so many insects were living at or near the upper limit in terms of daily temperatures ? so even moving into the shade was a futile exercise. “The direct effects of climate change on the organisms we studied appear to depend a lot more on the organisms’ flexibility than on the amount of warming predicted for where they live,” said Dr Tewksbury. “The tropical species in our data were mostly thermal specialists, meaning that their current climate is nearly ideal and any temperature increases will spell trouble for them.”
The scientists also warned that there will be other effects of global warming that could also have a serious impact on tropical regions, particularly on food crops.
“Our research focused only on the impact of changes in temperature, but warming also will alter rainfall patterns,” said Dr Deutsch. “These changes could be more important for many tropical organisms, such as plants, but they are harder to predict because hydrological cycle changes are not as well understood.”
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