Could the Nile Perch Invasion in Lake Victoria Have Succeeded without the Preceding Decrease of Its Prey?

The introduction of the Nile perch (Lates niloticus) into the largest tropical lake in the world and the following dramatic reduction in fish species diversity has made Lake Victoria in East Africa one of the paragon examples of man-made ecological blunders in the last century. The dramatic changes in Lake Victoria took place within a few years in the mid 1980s, almost 30 years after Nile perch was introduced. An unresolved question has always been why it waited so long when it could happen so fast. Long time series of environmental changes, eutrophication, productivity, and low and high trophic species changes and size compositions; indicate that the dramatic changes in the ecosystem encompassed areas of the ecosystem outside the control of the introduced top predator. Recruitment data indicate that Nile perch was strongly constrained when the abundance of the cichlids was high, and its explosive development did not take place until after these had nearly disappeared. With a size-based model we want to explore the alternative hypothesis that Nile perch was not able to become established when the abundance of the cichlids were high, and that its introduction therefore cannot be only explanation for the observed changes.