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Biodiversity: Drought, landscape fragmentation pose greatest threats to UK butterfly population

Landscape-level conservation projects critical to giving species some resilience in the face of climate change

A UK study suggests that large areas of intact habitat is the best way to buffer butterfly populations from extreme weather impacts. Photo courtesy Friedrich Böhringer via Wikipedia and the Creative Commons.

By Summit Voice

FRISCO — The gradual rise in global temperatures may have long-term effects on biodiversity, but some species — including UK butterflies — may be more threatened by extreme weather events related to climate change. Events like drought could push some insects toward extinction.

“We have provided the first evidence that species responses to extreme events may be affected by the habitat structure in the wider countryside; for example in the total area and fragmentation of woodland patches,” said lead author Dr. Tom Oliver from the NERC Centre for Ecology & Hydrology.

The UK has suffered from a number of severe droughts over the last few decades, including in 1976 and 1995. Under global warming, the frequency of such summer droughts is expected to increase. The intense summer drought in 1995 led to marked declines in insect species associated with cooler and wetter microclimates and scientists are interested in how to make species populations more resilient, so they can recover from extreme climate events.

The ringlet Aphantopus hyperantus is a grass-feeding butterfly commonly found close to woodland edges and known to be susceptible to drought effects. The researchers found that, following the 1995 drought, Ringlet populations not only crashed most severely in drier regions but, additionally, the habitat structure in the wider countryside around sites influenced population responses. Larger and more connected patches of woodland habitat reduced population sensitivity to the drought event and also facilitated faster recovery.

“Our results suggest that landscape-scale conservation projects are vital in helping species to recover from extreme events expected under climate change,” said co-author Dr. Tom Brereton, with Butterfly Conservation. “However, conversely, if we do nothing, the high levels of habitat fragmentation will mean species are more susceptible.”

Although many Ringlet populations did show some recovery following 1995-1996 population crashes, the long-term situation of the species in some parts of the UK is worrying. The researchers found that 18 percent of Ringlet butterfly populations continued to decline in the subsequent three years. The majority of populations showed positive recovery, although only 33 percent of populations showed complete recovery to pre-drought population levels within three years.

“The delayed recovery of butterfly populations is worrying given that severe summer droughts are expected to become common in some areas of the UK, for example, South East England,” said Dr.David Roy, with the NERC Centre for Ecology & Hydrology. “If populations don’t recover by the time the next drought hits, they may face gradual erosion until local extinction.”

The analysis was published in the scientific journal Ecography. It uses data on the Ringlet butterfly collected from 79 UK Butterfly Monitoring Scheme sites between 1990 and 1999, a period which spanned a severe drought event in 1995.

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