Crustacean diversity in relation to the size of water bodies: some facts and problems

SUMMARY.1 Data on the crustacean faunas of 207 lowland water bodies in Yorkshire, involving 125 species, are discussed in relation to site area. Not unexpectedly, large water bodies generally have the most diverse faunas, but the relationship is not a simple one so far as individual species are concerned. While many show a progressive increase in percentage occurrence from small to large water bodies, the reverse is true for others. 2 Chydorid cladocerans, of which twenty‐one species were recorded, show an unambiguous preference for large water bodies. While differences in habitat diversity appear insufficient to explain the almost seven‐fold difference in chydorid representation between ponds and large water bodies, there are also difficulties in attributing the situation to ease, or difficulty, of dispersal. The strategy of firmly attaching resting eggs to substrata employed by some chydorids is more likely to frustrate than to promote dispersal. 3 General habits, ecological preferences and feeding habits of the commonest species are analysed in an attempt to clarify the relation of number of species to size of water body and some paradoxical features of dispersal are noted. 4 Extrapolation from the data to very large lakes is shown to be misleading. Numerical data, even for a large number of water bodies, are no substitute for knowledge of the ecological requirements and tolerances of individual species. 5 Examples are given of the rapid colonization of newly formed ponds by small crustaceans. The relevance of such observations to the theory of island biogeography and to various ecological problems, and the possibility of experimental work using small crustaceans and small ponds are noted.