Butterflies need critical mass to outrace climate

As the climate warms, butterflies are expanding their distributions to the north—but that shift is only possible if the population of a species is stable or increasing.

The extent of distribution changes has varied greatly among species, however, with some showing rapid expansion and others showing none at all. But this variation can be explained by taking into account the abundance trends of species.

For those species with stable or increasing population trends that have been expanding their distributions, the amount of suitable habitat available in the landscape is important. The more habitat that is available, the faster a species can expand its distribution area.

Using data on butterfly distributions and abundances, collected by members of the public since the 1970s through citizen science projects, Louise Mair, a PhD student in biology at the University of York, and her colleagues examined factors limiting butterfly range expansion.

These data reveal that species that were previously restricted to southern England are colonizing northern England and Scotland. Butterflies have extended their distributions in this way because warmer climates have made northern regions increasingly more hospitable for these temperature-constrained insects.

The study concludes that conservation management must consider existing populations and ensure that species abundances are stable or increasing in order for them to be able to respond to climate change.

Increasing the amount of natural habitat in the landscape is an important conservation goal, which should increase the rate of distribution expansion for species with stable or increasing populations. However, habitat creation will not be effective for promoting range expansion by species whose populations are declining.

Many things, including local environment conditions, can affect population trends, and in recent decades most British butterflies have undergone population declines. More effort is needed to boost abundances within species’ current ranges in order to protect wildlife as the climate and landscape changes.

“My previous research revealed huge variation among butterflies in relation to their range expansion rates. It’s now clear from our new research that much of this variation can be accounted for once species’ population trends are known,” says Mair.

“Increasing habitat availability in the landscape has been suggested as a way to help species respond to climate change, but our research shows this will only be effective for species whose abundances are stable or increasing,” adds Professor Jane Hill.

The Natural Environment Research Council funded the study, which appears in Nature Climate Change.

Source: University of York

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