"Resting eggs of zooplankton and the paradox of enrichment:

Does analternative reproductive strategy adapted for food deficiency stabilize a　predator–prey system?"

仲澤　剛史

Although it is now clear that resting eggs of zooplankton affect plankton community dynamics in natural ecosystems, little theoretical research has considered resting-egg dynamics. Therefore, we investigated the possibility that resting-egg production by zooplankton would stabilize a phytoplankton–zooplankton system using simple mathematical models in which the density of viable resting eggs was explicitly expressed. In the models, we assumed that phytoplankton growth rate varied seasonally, zooplankton produced resting eggs seasonally or in response to food deficiency, and resting eggs hatched seasonally. Consequently, resting-egg production increased the risk of extinction in the zooplankton population under oligotrophic conditions. However, the models predicted the following stabilizing effects: a delay of bifurcation, a damping of the amplitude of population oscillations, an extension of the parameter space for persistent coexistence, and an increase in the minimum population density. These results support previous experiments and suggest that resting-egg production contributes to the stability and persistence of plankton community dynamics in natural ecosystems.