ABSTRACT
Much effort has been devoted to studying the distribution in some parts of Africa of freshwater snails in relation to variation in environmental conditions, within and among waterbodies. Common motives are to determine the distribution of snail hosts for schistosomes, in order to plan measures for controlling transmission of the parasites, and to assess the potential for an intermediate host to colonise man-made waterbodies. Examples of local snail faunas are described here, essentially in terms of general natural history, followed by discussions of the diversity of species, their relative abundance and associations among species. Seasonal changes in abundance are touched on briefly and are treated more fully in Chapter 11. Lastly, some influences on local distribution are examined, with particular attention to three biotic factors: dispersal, associations with aquatic plants and the availability of food (abiotic factors such as water chemistry are dealt with mostly in Chapter 10).
