Abstract
The Mountain Ringlet (Erebia epiphron) is the UK's only true montane butterfly, limited to the English Lake District and Scottish Highlands. Recent evidence highlights the loss of Mountain Ringlet populations and a distributional shift uphill. As such, there is a need to investigate the factors influencing the distribution of the butterfly and the effect that climate change could have on the persistence of the species. Three objectives were assigned to this study. Firstly, to identify the environmental factors which significantly influence the distribution of the Mountain Ringlet across the Lake District. This was undertaken using a generalised linear model (GLM) which uses presence records, background points and several environmental variables. Secondly, to identify if there is a difference in the capacity of Mountain Ringlets from different altitudes to thermoregulate. This was achieved by taking readings for butterfly body temperature and ambient air temperature from two populations which are found at low and high elevations. The third objective was to explore the hatch rate of eggs under different temperatures. This was accomplished by placing eggs collected from female Mountain Ringlets found at a high-elevation colony into one of two temperature treatments. These treatments included one at 25°C for 16 hours of light and 10°C for 8 hours of dark. The second treatment was set at 15°C for 16 hours and 8°C for 8 hours. GLM results showed that the chance of Mountain Ringlet presence was increased with higher levels of rainfall, lower summer temperatures, areas of volcanic geology, and higher autumn temperatures. Butterfly temperature sampling results showed that Mountain Ringlets from the low-elevation population are more capable at thermoregulation than those at high-elevation during higher air temperatures. This difference in the capacity to thermoregulate suggests local adaptation. Egg temperature treatment analysis showed no significant difference in the hatch rate of eggs under either treatment. Overall, the Mountain Ringlet populations in the Lake District clearly depend upon a stable climate, including precipitation and temperature, throughout the egg and adult stages of the life cycle. Any changes to the climate, particularly higher summer temperatures and variations in precipitation rates, could be detrimental to the survival of Mountain Ringlets. Consequently, the results indicate that climate change is threatening the persistence of the Mountain Ringlet in the Lake District.