Print PageSpecies invasion is one of the most serious concerns in conservation ecology. Although thousands of species have been introduced to novel habitats artificially, not all of them succeeded the subsequent settlement. The difference in their fates was mainly attributed to ecological characters of introduced species and resident communities, but also to invasion timing. For example, Namba & Takahashi (1993) showed that exogenous oscillations (similar to seasonal fluctuations) can create alternative stable states and result in the tight relationship between invasion timing and settlement success. Here we constructed a predator-prey model based on a chemostat system with zooplankton predator (rotifer) and phytoplankton prey (Chlorella) to investigate the effect of invasion timing on settlement success. We assumed trade-off between defense ability against predator and growth rate of prey. With this model, we searched for the condition at which bistability emerges and invasion timing affects settlement success.
Results/Conclusions
Our analysis revealed that there are various types of bistabilities in spite of the simple model structure. In addition, we found the conditions at which endogenous oscillations (limit cycles) can make invasion timing the determinant of settlement success. For example, more defended prey can succeed settlement to the system of predator and palatable prey if it invades when predator is abundant. If, on the other hand, defended prey invades when predator is scarce, its defense cost outweighs the defense advantage and fails to settle. Our results support the verbal prediction by Davis et al. (2000) and highlight the importance of introduction timing for reintroduction of previously-extinct native species.
