WASHINGTON - While global warming is expected to be strongest at the poles, it may be an even greater threat to species living in the tropics, scientists say. Tropical species are accustomed to living in a small temperature range and thus may be unable to cope with changes of even a few degrees, according to an analysis in Tuesday's edition of Proceedings of the National Academy of Sciences. "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...