Linking habitat use to range expansion rates in fragmented landscapes: a metapopulation approach

Temperature increases because of climate change are expected to cause expansions at the high latitude margins of species distributions, but, in practice, fragmented landscapes act as barriers to colonization for most species. Understanding how species distributions will shift in response to climate change therefore requires techniques that incorporate the combined effects of climate and landscape-scale habitat availability on colonization rates. We use a metapopulation model (Incidence Function Model, IFM) to test effects of fine-scale habitat use on patterns and rates of range expansion by the butterfly Hesperia comma. At its northern range margin in Britain, this species has increased its breadth of microhabitat use because of climate warming, leading to increased colonization rates. We validated the IFM by reconstructing expansions in five habitat networks between 1982 and 2000, before using it to predict metapopulation dynamics over 100 yr, for three scenarios based on observed changes to habitat use. We define the scenarios as "cold-world" (only hot, south-facing 150-250 degrees hillsides are deemed warm enough), "warm-world" in which 100-300 degrees hillsides can be populated, and "hot-world", where the background climate is warm enough to enable use of all aspects (as increasingly observed). In the simulations, increased habitat availability in the hot-world scenario led to faster range expansion rates, and to long-term differences in distribution size and pattern. Thus, fine-scale changes in the distribution of suitable microclimates led to landscape-scale changes in population size and colonization rate, resulting in coarse-scale changes to the species distribution. Despite use of a wider range of habitats associated with climate change, H. comma is still expected to occupy a small fraction of available habitat in 100 yr. The research shows that metapopulation models represent a potential framework to identify barriers to range expansion, and to predict the effects of environmental change or conservation interventions on species distributions and persistence.