In 1995, the United Kingdom experienced one of its worst droughts in more than 200 years, causing some populations of butterflies to plummet. With climate change expected to cause more frequent severe droughts particularly in the southern United Kingdom, people are increasingly worried about the region’s drought-sensitive butterflies. Now, scientists have found that widespread regional extinctions of these insects could occur as early as 2050.
“The prognosis is quite bleak,” says Tom Oliver, a co-author of the paper and an ecological modeler at the National Environment Research Council’s Centre for Ecology & Hydrology in Wallingford, England.
Previous studies have found that climate change will likely turn the United Kingdom into a refuge for many butterflies, as warming temperatures open up previously inhospitable habitats. But few of these studies have taken extreme events like the 1995 drought into account. In the new study, researchers first looked at long-term butterfly monitoring data from 129 sites in the southern United Kingdom and identified six drought-sensitive species that experienced widespread population collapses after 1995. Three in particular—the speckled wood, the large skipper, and the ringlet—are known to prefer wet woodlands.
To understand how these sensitive butterflies might respond to future dry spells, the scientists then used different scenarios of carbon dioxide emissions to predict the frequency of future droughts up to the year 2100. They then added in varying land-use scenarios to determine what the impact might be on the target butterflies. Under the “business-as-usual” scenario for emissions, they found that droughts similar to the 1995 event are expected to take place every year in the region. These annual droughts will prevent sensitive butterfly populations from recovering before the next one hits, causing their numbers to erode over time.
With this amount of climate change, no level of habitat restoration, the scientists conclude, will prevent populations of these drought-sensitive butterflies from going locally extinct by 2100. In landscapes that are highly fragmented from human activity like development and agriculture, the end could come as early as 2050, the researchers report today in Nature Climate Change.
The researchers say they expect the insects to persist in the region only if global warming stays under 2°C. If that climate scenario is combined with habitat restoration efforts, particularly those aimed at connecting habitats that have been fragmented by human activity, the average population has a much higher probability of survival—about 50%.
Restoring the connections between habitats that have been fragmented by human actions—instead of just focusing on maximizing total habitat area—is key if we want to give these butterflies a fighting chance, Oliver says. The study surprisingly found that reduced habitat fragmentation helped the butterflies recover more quickly after the 1995 drought than simply having a larger habitat in the first place.
When these natural areas are less fragmented, they have fewer edges, meaning they dry out less quickly and maintain enough moisture to nourish the nectar plants that feed the butterflies, Oliver says. Butterflies lucky enough to find wetter spots to wait out the drought can recolonize dry patches once the rains return. But they can do this only if those habitats are connected, with nectar plants acting like stepping stones across a creek.
“We don’t necessarily need a huge amount of restored habitat. Instead, we can do restoration in clever ways that reduce fragmentation, even if it’s just tiny pieces of land placed strategically,” Oliver says.
This is an “incredibly important” conservation message, says ecologist Camille Parmesan at Plymouth University in the United Kingdom. “It’s one that can be immediately applied in the U.K., and it can help inform how people think about similar species and land management and climate change in other areas.”
Still, she cautions, the study is a reminder that the butterflies have hard times ahead. “A lot of people misinterpret that 2°C threshold to mean that there’s no problems up to 2°C. But that’s really the point beyond which you get major shifts in biodiversity, major increases in species extinction, and major changes in the ability of systems to recover.” If we pass that threshold, “it doesn’t matter how much you preserve land, [these drought-sensitive butterflies] probably aren’t going to make it in parts of the U.K.”