The feeding strategies of two freshwater gastropods, Ancylus fluviatilis Müll. and Planorbis contortus Linn. (Pulmonata), in terms of ingestion rates and absorption efficiencies.

Radiotracer and gravimetric techniques were used to investigate the effects of starvation, temperature, body size and food quality on both the ingestion rates and absorption efficiencies of A. fluviatilis (an algal grazer) and P. contortus (a detrivore which utilises the bacterial fraction of its food). In the face of food supply disturbance snails showed a considerable potential for adaptation. Both intestion rates and absorption efficiencies increased with starvation, and ingestion rate increased with reductions in food quality. Absorption efficiencies were independent of temperature and Q values for absorption rates suggested that snails showed some acclimation to temperature disturbance. Food absorption was linearly related to body surface area but absorption efficiencies were to a large extent independent of age and size.The above homeostases are discussed in terms of their contribution to fitness and also in terms of the possible underlying causal mechanisms. The implications of physiological homeostases for ecological efficiencies are also discussed.