A popular assumption goes that because life on Earth survived past climate changes, the same will hold true for human-caused global warming.

Yet growing evidence contradicts this. Keeping up with the expected velocity of climate change, recent research shows, would require rates of evolution “largely unprecedented based on observed rates among vertebrate species,” according to Ignacio Quintero of Yale University and John Wiens of the University of Arizona.

Quintero and Wiens estimated these rates of evolution by essentially determining how much species changed within their climatic niche on a given branch of their evolutionary tree, then used the age of a species to estimate how quickly the climatic niche changed over time. Quintero and Wiens note the limitations of this approach, which are also discussed here in The Molecular Ecologist’s blog.

Despite these limitations, they say, the approach provides important insights, key among them being that typical rates of climatic niche evolution for hundreds of vertebrates over the last several million years are dramatically slower than those required to keep up with warming rates projected for 2000-2100. Keeping up, they found, would necessitate a rate of niche evolution more than 10,000 times faster than typically seen in most species studied.

In the past, species of birds, amphibians, crocodilians, mammals, turtles, and squamates (a group of reptiles) adapted to temperature changes at an average rate of less than 1 °C per million years, they found. Yet the climate could warm by a total of 4 °C or more by the end of this century (see the latest IPCC results).

Quintero and Wiens note that this does not necessarily imply climate change-induced extinction of species. Animals may have other adaptive mechanisms, besides microevolution, at their disposal.

Some could adapt, for example, by shifting their ranges  poleward or to higher elevations to track their climatic niches. Indeed the fossil record indicates this was dominant adaptive response to climate transitions between past glacial and interglacial cycles.

However, there are now unprecedented barriers to such movements:  many populations would now need to negotiate fragmented landscapes, and would come up against plantations, highways, urban development and coastal fortifications instead of finding viable habitat. (Skeptical Science provides a detailed discussion of these and other barriers to adaption in the face of climate change.)

Quintero and Wiens say their results on evolution are consistent with an inability to adapt already observed — some populations have died out from the low-latitude or low-elevation (roughly speaking, warm) boundaries of their ranges.

Sources:

Quintero & Wiens (2013) Rates of projected climate change dramatically exceed past rates of climatic niche evolution among vertebrate species. Ecology Letters 16: 1095.

Skeptical Science: Can animals and plants adapt to global warming?

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