ABSTRACT
Some factors influencing the local distribution of snails, particularly the biotic effects of plants and food supply, and dispersal ability, were considered in Chapter 9. The present chapter reviews the abiotic environment (physicochemical factors and habitat disturbance in the form of desiccation), with particular reference to observations on snail distribution and related laboratory experiments. These factors are considered further in Chapter 11, in relation to life cycles, growth and population dynamics. The three chapters are closely interrelated, since the successes and failures of local snail populations are reflected in the geographical distribution of their species. An investigator of freshwater snail distribution in Africa will learn much from the account by Økland (1990) of these organisms in Norway, which deals with small waterbodies as well as lakes.
