changes in temperature, humidity and nutrient availability seem to trumped the benefits of

　　increased carbon dioxide，” said researchers from the National University of Singapore.

　　45 percent of the species studied now reach smaller adult sizes than they did in the past. The

　　researchers pointed out that warmer temperatures and changing habitats, caused by climate

　　change, are possible reasons for shrinking creatures.

　　“We do not yet know the mechanisms involved, or why some organism are getting smaller while others are unaffected，” the researchers said. “Until we understand more, we could be risking negative consequences that we can't yet quantify.”

　　The change was big in coldblooded animals. Only two decades of warmer temperatures were enough to make reptiles smaller. An increase of 1 degree centigrade caused nearly a 10 percent increase in metabolism (新陈代谢). Greater use of energy resulted in tiny tortoises and little lizards. Fish are smaller now too. Though overfishing has played a part in reducing numbers, experiments show that warmer temperatures also stop fish growth. There is a recent report on warmer temperatures' negative effects on plankton, the base of the marine ecosystem.

　　Warmblooded animals weren't immune from the size change caused by climate change. Many birds are now smaller. Mammals have been miniaturized too. Soay sheep are thinner. Red deer are weaker. And polar bears are smaller, compared with historical records.

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