REFUGIAL POPULATIONS AT TRAILING-EDGE RANGE MARGINS: ATTRIBUTES, SURVIVAL AND CONSERVATION

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Many species currently survive as localised, refugial populations in regions where they used to be more widespread under more favourable past climatic conditions. These species survive in localised habitats and/or microclimates that are atypical of the surrounding region; for example, a cold-adapted species in Britain might survive on a locally cold, north-facing site when the climate warms. Refugia have been extremely important in allowing species to survive past climatic changes, and are likely to be so again under anthropogenic climate change. Despite this, the local conditions that support population refugia are poorly understood. Thus we have little idea of the attributes (locations, habitats, microclimates) of sites where species may persist in future as the climate changes. Understanding these attributes is vital for informing future conservation policies as well as for developing a deeper fundamental scientific understanding of the dynamics of species' geographic distributions. We will take advantage of the opportunity presented by anthropogenic climate change to observe the creation of refugial populations directly, by studying four species of northerly-distributed butterflies in Britain. Butterflies are ideal study species for this project because there are excellent distribution records in Britain over the past four decades of climate change, and because local microclimate and microhabitat conditions affect all butterfly life stages, from birth to death. We will re-survey sites in Britain for which we have historical distribution data since the 1970s, and which we re-surveyed in 2004-05, to determine where species have survived, and where they have become extinct. We will use dynamic population models that incorporate environmental information for species to identify the local microclimatic and habitat characteristics of locations where populations have survived since the onset of anthropogenic climate change in the 1970s. We will examine the generality of our butterfly findings by studying climate refugial formation in other northern invertebrates. We will then use our models to project the consequences of future climatic changes for species, to the year 2100, and determine the degree to which refugia coincide with the locations of existing protected areas in Britain.The proposed work will provide the first investigation of, and predictive models for, the attributes of locations that promote population persistence in range retreating species. The project will address fundamental questions about the dynamics of species' ranges under climate change, as well as producing results of considerable practical value for policy makers. It will open up a new avenue of research on understanding the impacts of climate change on biodiversity, and provide a concrete body of scientific evidence to inform the debate on developing effective conservation strategies under climate change.