Biologists have been warning for years of animals that are at risk of going extinct because their habitats are warming faster than they can adapt. A newly published meta-analysis shows this applies to common species as well as those already considered endangered.
Earth has warmed and cooled many times. Each cycle has been responsible for the loss of some species, but most change has been slow enough the vast majority of animals have managed to adapt and found a place in the new world. Some have done this by shifting their habitat. Others relied on genetic change, with those whose DNA was best suited to the new conditions more likely to pass on their genes. Any loss of species was balanced by the appearance of new ones.
With global temperatures rising faster than they have for millions of years, however, the challenges are greater. So how are animals doing? Not well, according to Dr Viktoriia Radchuk of Leibniz Institute for Zoo and Wildlife Research and a large team of co-authors, even if you leave out all those being wiped out through habitat loss, invasive species, or poaching.
Reviewing 10,090 peer-reviewed abstracts and 71 full papers on 4,835 species Radchuk reports in Nature Communications animals are adapting to climate change, but seldom fast enough to keep up. Most of the studies Radchuk found were on birds, but the few on other branches of the tree of life, such as one on roe deer, produced similar results.
Radchuk found many examples of changes in animals' bodies and behavior recorded over recent decades, with a strong trend in the direction predicted for rising temperatures.
The pattern is strongest in changes to the timing of reproduction and migration, likely due to the climate-driven shift in seasons becoming earlier, later, or prolonged. Animals are breeding earlier in spring as the climate warms and the season is occurring earlier in the year, but some are changing faster than others. This can disrupt ecosystems, for example when the timing of hatching no longer matches the peak availability of food.
Not all the evidence is so convincing. Despite exceptions, most animals follow Bergmann’s rule, being larger in colder climates. Although some studies have reported wild birds are shrinking, they have left open other interpretations, such as a decline in food supplies preventing individuals growing to their potential. Radchuk and co-authors explain most studies lack the observations over multiple generations needed for this sort of work, or fail to rule out alternative explanations.
Overall, the paper concludes: “Responses may partially alleviate negative fitness effects of changing climate”. Most often, however, these changes are “lagging behind at a constant rate”. Animals might catch up if warming pauses, but if it continues long enough the lag could become fatal. Since the studies were skewed towards common species, where data collection is easiest, the authors fear for rarer animals.
