EFFECT OF PROGRAMMED CIRCADIAN TEMPERATURE FLUCTUATIONS ON POPULATION DYNAMICS OF BULINUS TROPICUS (KRAUSS) AND LYMNAEA NATALENSIS KRAUSS (GASTROPODA: MOLLUSCA)

Abstract

Until now all life-table studies on Bulinus tropicus (Krauss) and Lymnaea natalensis Krauss involving temperature as the variable factor have been conducted at constant temperatures. This study evaluates the effect of programmed, circadian temperature fluctuations, ranging from 18 to 28 °C and 20,5 to 25,5 °C and a constant temperature of 23 °C on the population dynamics of these two species. The highest innate capacity of increase, net reproduction rate and mean mass per snail were obtained at the higher daily temperature fluctuation to which they were subjected. No differences in the population statistics for either species emerged as far as the other two temperature regimes were concerned.