A new study by the University of York has shown how a butterfly species changed its diet and spread northwards in response to the changing climate.
The study found that warmer summers have allowed the Brown Argus Butterfly to complete its lifecycle by using wild Geranium plants, rather than the Rockrose plants they had previously been using. Wild Geraniums are suitable for the butterflies during warm years, but not during cold summers. This appears to be because Rockrose almost always grows in sun-exposed southern facing slopes, while Geraniums grow in a wide variety of cooler areas. So the Geraniums are only suitable for the caterpillars during warmer years.
Geraniums are widespread throughout the British countryside, so this change in diet has allowed the butterflies to vastly increase their range. Over only the past 20 years they have spread 79 km north, while becoming very common in the southern regions where they had previously been scarce and undergoing decline. The warming climate has created a boom in their population, allowing them to use a previously unexploited resource to extend their range and influence.
Lead author PhD student Rachel Pateman, of the University of York’s Department of Biology and the NERC Centre for Ecology & Hydrology, said: “Many species are shifting their distributions northwards as the climate warms, but this previously scarce species has surprised everyone by moving its range at over twice the average rate.”
Co-author Chris Thomas, Professor of Conservation Biology at York, said: “Because wild Geraniums are widespread in the landscape, the butterflies can now move from one patch of host plants to next and hence move rapidly through the landscape — expanding their range generation after generation.”
Co-author David Roy, from the NERC Centre for Ecology & Hydrology, said: “The change in diet represents a change to the interactions between species — in this case between a butterfly and the plants that its caterpillars eat — caused by climate warming. Changes to the interactions between species are often predicted to alter the rate at which species shift their distribution in response to climate change; and now we have demonstrated this in nature.”
Co-author Richard Fox, from the charity Butterfly Conservation, said: “It is important that we understand how and why species are responding to climate change. Such research would not be possible without the thousands of records of butterflies our dedicated volunteers have collected over many decades, which have allowed us to detect these long term changes.”
Rachel Pateman said: “This study has highlighted that species do not respond to climate change in isolation, and that climate change affects how species interact with one another. In the case of the Brown Argus butterfly, changes in interactions with its food plants have helped it to respond to climate change very rapidly. However, changes to interactions may hinder other species, potentially putting them at risk of extinction.”
Co-author Professor Jane Hill, of the Department of Biology at the University of York, said: “There will be winners and losers from climate change. It is important that we begin to understand how the complex interactions between species affect their ability to adapt to climate change so we can identify those that might be at risk and where to focus conservation efforts.”