Abstract

The use of volunteers (often now called ‘citizen scientists’) to systematically map the distribution of plant species was pioneered by the Botanical Society of the British Isles in the Atlas of the British Flora (1962), compiled by the Cambridge botanists Frank Perring and Max Walters. Their techniques have been adapted for mapping the distribution of many groups of animal and plants in Europe, North America and elsewhere as ‘the Atlas movement swept over the face of the earth’. In time the recording exercise was repeated for the more popular groups, so that birds, butterflies, dragonflies and flowering plants in Britain have now been mapped and remapped. Comparison of the results of these mapping exercises is a vital source of information on changes in range, including the decline of some species and the expansion of others. However, simple comparison of the results of repeat mapping, or even sophisticated numerical analyses, may be misleading. In interpreting apparent changes, a knowledge of ‘cultural’ changes in biological recording is often essential. Scientists interested in distributional change therefore find themselves venturing into the territory of historians.