The invasion of Nile Perch (Lates niloticus) into Lake Victoria is one of the iconic examples of the destructive effect of an introduced species on an ecosystem, but few convincing explanations of why Nile Perch only increased after a two decade lag-time since introduction exist. We consider a mathematical model of the interactions between Nile Perch and its (Cichlid) prey including, as a crucial element predation and competition between juvenile Nile Perch and Cichlids. We consider the potential for invasion of Nile Perch through its lifetime reproductive output or R₀.

Results/Conclusions

Preliminary results support the hypothesis (Goudswaard et al. 2006, DOI:10.1007/s10641-006-9180-7) that fishing on cichlids may have triggered invasion of Nile Perch through release from depensatory effects of Cichlids on Nile Perch recruitment. We find that the negative effects of predation by and competition with Cichlids reduces the potential for invasion of Nile perch and may lead to a dramatic switch between alternative states: one characterized by low levels of Nile Perch and high levels of cichlids, the other by high levels of Nile perch and low levels of cichlids. We illustrate how interactions between fishing on nile perch and fishing on haplochromis may lead to switches between these two states.