Intraspecific variation in habitat availability among ectothermic animals near their climatic limits and their centres of range

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Abstract
1. In a modelling exercise, the quantity and distribution of habitat patches within a heathland biotope for four ectothermic heathland animals (silver‐studded blue butterfly [Plebejus argus], a red ant [Myrmica sabuleti], heath grasshopper [Chorthippus vagans] and sand lizard [Lacerta agilis]) were compared in space and time assuming two climates: that experienced at the northern edge of the species’ ranges and that 300–400 km further south, where mean summer temperatures are 2–3 °C warmer. 2. Habitats both at the northern edge of their ranges and 300–400 km further south for the four species were defined qualitatively from existing sources and then expressed quantitatively in terms of the attributes recorded in the Dorset Heathland Survey. The Survey was then used as a GIS to map the occurrence of the habitats of the four species under two climates and a decade apart. 3. The model predicts that an increase of 2–3 °C can result in a large increase in the area of habitat available to these north temperate species, that the length of time that individual patches of successional habitat may be occupied increases and that the distance between habitat patches within the biotope decreases. 4. The warmer conditions should result in a more stable metapopulation structure for P. argus, with fewer metapopulations existing in the landscape but each, on average, containing a greater number of larger and more stable constituent populations. 5. These predictions are of significance to ectothermic species which currently live at the northern limits of their ranges in the British Isles. The reverse effect is likely for species at the southern limits of their ranges. Conservationists who wish to maintain the status quo may be able to reduce some effects of these changes by appropriate habitat management.