Redistribution of the potential geographical ranges of Mistletoe and Colorado Beetle in Europe in response to the temperature component of climate change

1. Following the method of Jeffree & Jeffree (1994), mean temperatures of the coldest (x) and warmest (y) months of the year in the geographical ranges of Viscum album and Leptinotarsa decemlineata were used to construct ellipsoidal probability regions for the range of each species in temperature space. 2. Assuming that species responsiveness to temperature remains constant, the temperature probability ellipsoids may be used to interpret both the potential geographical range of the species and its potential redistribution in response to the temperature component of past or future climatic changes. 3. Temperature changes Delta x and Delta y for UKHI and UKTR GCM scenarios for a double CO2 were plotted as vectors in two-dimensional (x, y) temperature space, enabling the magnitude and direction of temperature change at each geographical location to be visualized. 4. Interactions in x, y temperature space between the temperatures of geographical locations and the temperature probability ellipsoids were used to map those areas of Europe in which the combination of summer and winter temperatures would be suitable for the species in various temperature change scenarios. 5. The direction of potential migration of each species was found to be sensitive to seasonality both of existing temperatures and of the increments Delta x and Delta y, and cannot therefore be interpreted from annual mean temperature change alone. 6. Under the increasingly oceanic temperature regimes in Europe indicated by the UKHI and UKTR GCM scenarios the potential range of Viscum album is only likely to extend north and east into parts of Europe currently with a regime that is both cooler and more continental than in the present species distribution. 7. UKHI and UKTR scenarios of climatic warming are likely to be unfavourable to northward extension of the range of Viscum album in Britain, and may result in the loss of the species where current annual temperature range is reduced. 8. By contrast, in the same temperature change scenarios, the potential geographical range of summer and winter temperatures suitable for Leptinotarsa decemlineata may extend into Britain as far as the north of England.