Growth and fecundity in Bulinus truncatus (Gastropoda : Planorbidae) in intraspecific and interspecific competition with Melanopsis praemorsa (Gastropoda : Melanopsidae)

Under semi-field conditions, the growth and fecundity of Bulinus truncatus decline when density is higher in both intraspecific and interspecific comp etition with Melanopsis praemorsa. This latter considerably affects the lif e history traits of B. truncatus. The growth and fecundity of B. truncatus are significantly increased in the presence of M. praemorsa at Bt/Mp (B. tr uncatus / M. praemorsa) ratio of 1/1. In constrast, at the Bt/Mp ratios of 1/3, 1/8 and 1/17, the growth, but not the fecundity, is inhibited. This co uld be attributed to the distinct behaviour of M. praemorsa at the time of density changes. The niche overlap, hence the interspecific competition bet ween the two species, becomes more important at higher densities of M. prae morsa, whereas the dietary niches of both species are different at lower de nsities. The data obtained suggest that high densities of M. praemorsa are involved in B. truncatus population declines in many Schistosoma haematobiu m focuses within the Haouz region of Morocco.