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In three areas of the English Midlands, composition and diversity of hedgerow snail faunas are influenced both by historical and environmental differences between hedges. Soil aciditv and climate are the most important environmental factors. Hedges originating in or near woodland have richer faunas than those planted in open fields, and some snail species are indicators of woodland origin. Snail diversity also increases with the age of the hedge, but this effect is slight in hedges over 100 years old. It is suggested that these differences are primarily due to the poor dispersal of snails rather than to existing environmental differences between hedges of differing age and origins, and the results are compared with the very similar ones obtained for plants. Historical influences on the distribution ol slow-dispersing organisms may be of very general importance, even in comparisons of adjacent habitats with considerable temporal stability. |
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