Planet Earth Online

Butterflies less choosy in a warm climate

24 September 2009, by Tamera Jones

Scientists report in the journal Ecology Letters that the climate of a region can affect the number of habitat types butterflies can live in. This means that butterfly species' niches are broader in southern British locations than in the north.

'This makes sense: we know that butterflies are more abundant in the south than the north of the country. Also, milder winters in southern Britain mean there are more habitats for butterflies to survive in, so more make it to the next summer. In the north, they have to be choosy and seek out their favourite habitats, so not as many will survive,' says lead author, Dr Tom Oliver from the Centre for Ecology & Hydrology (CEH).

'In Scotland, which is at the range edge for many species, butterflies can only survive in the best possible habitats,' he adds.

The research suggests that as global warming changes the climate across the whole of the country, many butterflies will be better off and able to live in a wider variety of habitats in northern Britain.

But Oliver warned, 'Climate models predict that a warmer climate will bring an increase in climatic extremes like cold snaps and heavy rainfall, neither of which is good for butterflies.'

The research, by scientists at CEH, Butterfly Conservation and the University of York, means conservationists may need to consider the effect of a changing climate when planning habitat conservation and restoration.

'If the types of habitats that species use change depending on where you are in the country, a one-size-fits-all approach to conservation isn't necessarily going to work,' says Oliver.

Oliver's research stemmed from previous work carried out by other scientists which analysed where the silver-spotted skipper (Hesperia comma), a grassland butterfly, preferred to live. Researchers found that in the south, the butterfly was happy to live 'in many different types of grassland'.

But in the north, researchers only found the butterfly on south-facing grassland. As the climate has warmed over time, the butterfly has spread, which made the scientists wonder if it has more choice of habitat.

To test this idea, Oliver and his team analysed data collected by a nationwide network of butterfly enthusiasts between 1976 and 2007 for the UK Butterfly Monitoring Scheme.

Around 800 enthusiasts walk along transects spread across the country once a week during the butterfly flight season - April to September - each year. They then send their data to Butterfly Conservation and CEH for analysis.

The data analysed by the research team covered 41 of the 55 British butterfly species across climatic gradients and various habitat types across the country. 'We'd like to have looked at all British species, but some species are so rare, there just isn't enough data for them,' says Oliver.

The results show that the majority of butterflies prefer to live within a small number of habitat types when climatic conditions are difficult. Where winters are cold or have high rainfall, the harsh climate makes some habitat types that would be suitable in the south not so welcoming in the north. This restricts butterflies to their favourite habitats.

'Besides climatic suitability, an additional reason for these results could be that in the south, when conditions are good, the best habitats get filled up, because there's not enough food to go round, so butterflies are forced to spread out. But in the north, there's not the same competition for the best habitats,' says Oliver.

The researchers say that people may start seeing rarer butterflies like the Small Copper and the Gatekeeper in their back gardens or in their local parks. These butterflies favour grassland and as the climate warms, we may see changes in the types of habitats these species use.

Many British butterfly species are in decline, with only a few species that are doing okay. Oliver says the next step is to look in detail at how populations have changed over time.

Keywords: Biodiversity, Environmental change, Europe,

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