Shrink or sink

摘要

The polar bear is the largest land carnivore on the planet. Male bears typically weigh around 400 kilograms, and a few grow up to 600 kg. At least, that's how big they used to be. In Alaska, and perhaps elsewhere, polar bears are no longer growing as large as they did just two decades ago. At the other end of the spectrum, the saffron-bellied frog of Borneo is so small - just 20 millimetres long - that it is difficult to spot despite its marbled blue back and brightly spotted underside. And it is becoming even harder to spot, because it too is shrinking.