Population Biology of the Freshwater Snail Bulinus globosus on the Kenya Coast. I. Population Fluctuations in Relation to Climate

Abstract

Bulinus globosus [a bilharziasis vector] populations were sampled weekly in 2 reservoirs over 2 yr, using plastic sheet snail traps and mark recapture techniques to measure density, growth rates and reproduction. Captive cohorts were raised in netted boxes in the reservoirs to measure age specific reproduction and egg viability. Growth rates were used to identify snail cohorts, and life tables were constructed to measure mortality rates and the intrinsic rate of natural increase (rm). Values for rm were inversely related to mean water temperatures, with no positive values when the mean water temperature exceeded 28.5.degree. C during a cohort''s early reproductive phase. Rainfall (and associated environmental variables) appear to influence the carrying capacity of the snail habitat, so that in both reservoirs, populations increased fastest and to the highest densities when large amounts of unseasonal rain fell during the coolest months.