Greenhouse gases released by humans are causing the world to warm, and with that warming comes increased stress on many of the planet’s plants and animals. So great is this stress that many scientists believe we are currently in the midst of the “sixth extinction,” when entire species are disappearing at up to 10,000 times faster than before the Industrial Era. But scientists weren’t sure which ecosystems and which species are most at risk. New research recently published in nature climate change, shows for the first time that the focus on species-level risk masks a large variability in temperature tolerance, even within the same species, and that this variability is larger in marine than in terrestrial species. The findings have immediate implications for management and conservation practices, and offer a window of hope for efforts to adapt to a rapidly warming world.
“One of the most important biological discoveries of the last century is that evolution can happen much faster than previously thought,” says Brian Cheng, professor of marine ecology at the University of Massachusetts Amherst and senior author of the publication. “One of the consequences of this is that different populations of the exact same species can adapt to their local environment more easily than traditional biology would have thought possible.”
It turns out that this rapid, localized adaptation can help ensure survival in a warming world.
By conducting a meta-analysis of 90 previously published studies, from which Cheng and his co-authors extracted data on 61 species, the team was able to construct a set of “thermal upper limits” — specific temperatures above which each species couldn’t survive. However, when they zoomed in further and looked at 305 different populations from this pool of 61 species, they found that different populations were present same sea species often had very different thermal limits. This suggests that some populations have evolved different abilities to tolerate high temperatures. So the key is to connect different populations of the same species together so that the populations that have adapted to the higher temperatures can pass that benefit on to the populations with the lower thermal limits.
In other words, imagine a widespread marine species like the tiny Atlantic killifish, found from the warm coast of Florida in the United States north to the cold waters of Newfoundland in Canada. Northern killifish populations may be better able to withstand warmer waters if some of their southern relatives are able to naturally shift their range north.
“Scale is important,” says Matthew Sasaki, a marine biologist and evolutionary ecologist who completed this research as part of his postdoctoral fellowship at the University of Connecticut and is the lead author of the paper. “The patterns you see within species aren’t the same as you see within species, and the broader story doesn’t necessarily align with what’s happening at the local level.”
In another twist, the team, funded by the National Science Foundation and made up of biologists specializing in both terrestrial and marine ecosystems, discovered that this within-species variability was primarily a trait of animals that live in the ocean and in tidal areas. Populations of widespread species living on land or in freshwater have far greater homogeneity in their thermal boundaries and may therefore be more sensitive to rising temperatures. On land, on the other hand, plants and animals can use the microclimate to cool down and avoid extreme temperatures, for example by seeking shady spots.
Taken together, the research suggests that a one-size-fits-all approach to conserving and managing all species will not work. Instead, the authors write, we need to understand how populations have adapted to their local conditions if we are to predict their vulnerability to changing conditions. A more effective approach would be to ensure that marine species can find large swaths of undamaged habitat throughout their ranges, allowing different populations of the same species to mix and pass on the adaptations that help them survive warmer waters. And on land, we need to conserve large expanses of cool ecosystems — such as old-growth forests — that terrestrial species can use as refuges.
“The glimmer of hope here,” says Cheng, “is that with conservation policies tailored to each population group, we can buy them time to adjust to the warming world.”
Materials provided by University of Massachusetts, Amherst. Note: Content can be edited for style and length.