Inter-guild differences and possible causes to the recovery of cichlid species in Lake Victoria, Tanzania.

Abstract

Until the 1970s, the fish fauna of Lake Victoria was dominated by 500+ endemic haplochromine cichlid species in which detritivores was the dominant group followed by zooplanktivores. With the upsurge of Nile perch in the 1980s, a strong decline of haplochromines occurred. During the1990s, a resurgence of some haplochromine species was observed and the abundance of detritivores and zooplanktivores reversed. In establishing the status of the recovering haplochromines in the period 2006-2008, the study has given evidence for a strong resurgence of the detritivorous, zooplanktivorous and oral mollusc shelling species, while other trophic groups were rare or absent. The recovered haplochromines extended their habitats. Differences in diet of detritivores and zooplanktivores and differences in predation pressure by Nile perch on the two trophic groups have been tested as potential ecological factors for their differential resurgence. It was found that both groups had switched from a restricted to a more diverse diet, with a greater overlap. Further, the study shows that resurgent haplochromines became the major prey of Nile perch, but there was no differential predation effect by Nile perch on detritivores and zooplanktivores. Thus, it is not likely that these factors played an important role in differential resurgence of the two trophic groups in Lake Victoria.