Evolution normally helps organisms positively adapt to changing circumstances, but climate change may turn that on its head. A model of how some species could rapidly evolve in response to increasingly extreme events, such as storms, has found that mutations could actually drive some small, vulnerable populations to extinction.
This is because traits that help animals or plants that survive extreme events can be a disadvantage in normal situations. 鈥淏y the next generation, the environment has already gone back to normal,鈥� says Kelsey Lyberger at the University of California, Davis. 鈥淵ou never get to benefit from the change.鈥�
Many animals are already evolving in response to long-term global warming. For instance, owls in Finland are getting browner as snow cover declines and plants in California are flowering earlier as it gets drier.
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This process should help many populations adapt, but not all will be able to evolve fast enough. Climate change is expected to become a major cause of extinction along with habitat loss and over-exploitation.
It is also clear that extreme events fuelled by global warming, such as more extensive wildfires, can drive vulnerable populations to extinction. For instance, in 2019, the category 5 Hurricane Dorian may have killed the last few individuals of a bird called the Bahama nuthatch.
Such extreme events can also produce rapid evolution. Lizards on the Caribbean island of Dominica evolved a superstrong grip after category 5 Hurricane Maria in 2017聽鈥� likely because only lizards that managed to cling onto branches survived. But it is possible that these lizards have to consume more food to maintain this extra strength, making them a bit less likely to survive in normal conditions.
Such observations inspired Lyberger and her colleagues to create a mathematical model that allows the effects of environmental changes of different duration to be compared.聽The results suggest that brief changes, such as storms, can reduce the fitness of survivors in normal conditions to such an extent that their numbers decline rather than recovering. The risk is greatest for small populations confined to a small area, such as an island.
The size of the effect depends on how extreme an event is, how often such events happen and how much genetic variation there is in a population. While having lots of genetic variation is usually thought to boost a population鈥檚 odds of survival, more varied populations are more likely to end up 鈥渕aladapted鈥� after an extreme event, says Lyberger.
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