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

1. In a modelling exercise, the quantity and distribution of habitat patche s within a heathland biotope for four ectothermic heathland animals (silver -studded blue butterfly [Plebejus argus], a red ant [Myrmica sabuleti], hea th grasshopper [Chorthippus vagans] and sand lizard [Lacerta agilis]) were compared in space and time assuming two climates: that experienced at the n orthern edge of the species' ranges and that 300-400 km further south, wher e mean summer temperatures are 2-3 degrees C warmer. 2. Habitats both at the northern edge of their ranges and 300-400 km furthe r south for the four species were defined qualitatively from existing sourc es 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 dec ade apart. 3. The model predicts that an increase of 2-3 degrees C can result in a lar ge increase in the area of habitat available to these north temperate speci es, that the length of time that individual patches of successional habitat may be occupied increases and that the distance between habitat patches wi thin the biotope decreases. 4. The warmer conditions should result in a more stable metapopulation stru cture for P. argus, with fewer metapopulations existing in the landscape bu t each, on average, containing a greater number of larger and more stable c onstituent populations. 5. These predictions are of significance to ectothermic species which curre ntly 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 reduc e some effects of these changes by appropriate habitat management.