Zabulon Skipper: Butterfly harbinger of climate biodiversity doom?

'Haven't you guys heard of evolution,'

Opinion A volley of studies into the likely effects of climate change on various animal species - and thus on biodiversity worldwide - have come out in the last few days. The headliner, examining butterflies in Massachusetts, seems to indicate that rising temperatures are having powerful ecological effects: but another pair of studies showed that other factors may be more powerful than warming, and yet another appears to indicate that dangers are being overblown.

First up is the butterfly research, published in hefty climatology mag Nature Climate Change. In this study, Harvard boffins trawled through 19 years' worth of records produced by amateur members of the Massachusetts Butterfly Club.

According to a Harvard uni statement announcing the research:

Subtropical and warm-climate species such as the giant swallowtail and zabulon skipper—many of which were rare or absent in Massachusetts as recently as the late 1980s—show the sharpest increases in abundance. At the same time, more than three quarters of northerly species—species with a range centered north of Boston—are now declining in Massachusetts, many of them rapidly.

"For most butterfly species, climate change seems to be a stronger change-agent than habitat loss. Protecting habitat remains a key management strategy, and that may help some butterfly species. However, for many others, habitat protection will not mitigate the impacts of warming," comments study author and Harvard postdoc Greg Breed.

Open and shut, then - the warming seen from the 1980s to the turn of the century has already seriously affected butterflies, and projected future warming will surely mean more serious consequences. Many people, indeed, have not hesitated to link recent severe weather events in the States to global warming - despite a refutation of this idea from no less a body than the IPCC. But as it is well known to all followers of pop-science coverage that just one butterfly beating - or not beating - its wings can have major effects on the weather in the northeastern United States, it seems only reasonable to suggest that the invading Zabulon Skippers, apparently wafted into Massachusetts by global warming, are responsible for recent storms, floods, heatwaves etc.

Even so, there still seems to be some uncertainty as to the effects of rising temperatures on ecologies and species in general (we'll take it as read that global temperatures are indeed set to increase, despite having flatlined in recent years).

Two other new studies lately announced cast some doubt on any simplistic relationship between temperature and species migrations.

"Our results redefine the fundamental model of how species should respond to future climate change," says Morgan Tingley of UC Berkeley, describing his and his colleagues' work studying bird populations, recently published in Global Change Biology. "We find that precipitation changes can have a major, opposing influence to temperature in a species' range shift."

Another study into squirrel populations, published in the Proceedings of the Royal Society B, seems to indicate that human activities such as irrigation can safeguard species which would otherwise be in serious trouble.

Or, in summary, scientists don't really know what will happen to any given species in future.

"Taken together, these two studies indicate that many species have been responding to recent climate change, yet the complexities of a species' ecological needs and their responses to habitat modification by humans can result in unanticipated responses," says Steven Beissinger, professor at UC Berkeley and senior boffin on both studies. "This makes it very challenging for scientists to project how species will respond to future climate change."

Yet another recent study announced in the past week goes still further, suggesting that the danger to Earth's biodiversity posed by rising temperatures has been exaggerated.

"It is believed that climate change poses a greater risk to tropical cold-blooded organisms (ectotherms), than temperate or polar species," explains Dr Richard Walters of Reading uni. "The tropics are home to the greatest biodiversity on earth, so it imperative that the risk of extinction caused by climate change is understood."

According to Walters, however, researchers to date have forgotten to factor in one of the most powerful factors in biology - namely that of evolution. Scientists predicting doom for the huge diversity of tropical life in a warming world have failed to calculate that species are likely to evolve their way out of trouble and become able to cope with changed conditions.

"Potential adaptation to climate change has not been considered in previous extinction models - so we tested this theory with a model forecasting evolutionary responses," says the doc.

Walters and his colleagues found that once the effect of evolution is allowed for, the apparent menace to the global ecology is found to have been overstated.

"Our model shows that the evolutionary advantage of a shorter generation time should compensate species which are adapted to narrow temperature ranges," he says.

"While many questions remain, our theoretical predictions suggest tropical species may not be as vulnerable to climate warming as previously thought," comments Walters.

That latter study is published here, in the the British Ecological Society's journal Functional Ecology. ®

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