A new study has found that warmth-loving butterfly species in Great Britain occupy a more narrow range of habitats despite three decades of climate warming. This means that British butterflies are likely to be found in a smaller range of habitats (for example woodlands, grasslands and hedgerows) than they were in the 1970s.
The analysis, published this week in the scientific journal Global Change Biology, used data from 77 UK Butterfly Monitoring Scheme sites collected between 1977 and 2007. Over that period, average temperatures have risen in Great Britain.
The study was led by Dr Tom Oliver from the NERC Centre for Ecology & Hydrology (CEH) in collaboration with researchers at the University of York and the charity Butterfly Conservation.
Previous research had shown that many warmth-loving species have broader habitat associations, i.e. use a wider range of habitats, in warmer locations. Therefore, scientists had expected that, over time, species may have expanded in their habitat associations in Great Britain, as the climate had warmed.
In contrast to these expectations, the research team found that 74% of the 27 butterfly species tested showed marked contractions in their habitat associations. These contractions in habitat associations were associated with smaller populations and potentially linked to a decline in habitat quality over the last three decades.
The researchers suggested that declines in the breadth of butterfly habitat may have resulted from changes in the quality of many habitat types for butterflies in Great Britain over the past 30 years. Many natural habitats such as woodlands and hedgerows have become more shady over time due to changes in management and increased use of fertilisers. This means that, ironically, despite the climate having warmed in Great Britain over the last three decades, warmer microsites, which are required by many warmth-loving butterfly species, may be less common.
Lead author Dr Tom Oliver, CEH, said, “The fact that species do not occur in as broad a range of habitat types as they once did means many people are less likely to enjoy seeing them. In addition, because the species are found in fewer habitat types, they may be more vulnerable to certain events, such as droughts, where those habitats become unsuitable.”
Many insect species are at the northerly limit of their distributions in Great Britain. Hence, they are limited by colder temperatures and under climatic warming are expected to be able to use a broader range of habitats. However, although some species did expand their habitat associations, for many species habitat breadth had declined, especially for species associated with very open habitat types, such as short-turf grassland.
Co-author Tom Brereton from Butterfly Conservation said, “The Common Blue butterfly, despite its name, is now much less common than it was 30 years ago. We found population densities had declined by 42% and the butterfly is now much more restricted to grasslands and increasingly rare in other habitat types such as hedgerows and woodlands.”
Co-author Professor Chris Thomas from the University of York added, “The fact that most butterfly species have shown habitat contractions over the past 30 years suggests that the negative effects of other drivers, such as habitat degradation, may have outweighed any benefits of climate warming for these warmth-loving species.”
The paper, "Habitat associations of thermophilous butterflies are reduced despite climatic warming", by Tom H. Oliver, Chris D. Thomas, Jane K. Hill, Tom Brereton and David B. Roy, is published in Global Change Biology (2012), doi: 10.1111/j.1365-2486.2012.02737.x
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