The influence of seasonal forcing on the population dynamics of ecological systems

Abstract

Seasonal forcing represents a pervasive source of environmental variability and it has been shown to be important in generating the cycles observed in many ecological and epidemiological systems. We use a combination of bifurcation analysis and simulation to understand the impact of seasonality on population dynamics, with a focus on predator-prey and host-macroparasite systems. Multi-year cycles with a wide range of periods, quasi-periodicity and chaos are found. We consider the importance of the unforced dynamics in a predator-prey system by contrasting the e ect of seasonality when the underlying behaviour is oscillatory decay to the equilibrium or limit cycles. The limit cycles case shows a wider range of dynamics and multiple solutions. The e ect of variations in the seasonal forcing term are analysed in a predator-prey model by changing the breeding season length, using the vole system in Fennoscandia as a case study. It is found that the period of the multi-year cycles increases as the breeding season length decreases. By studying a general host-macroparasite system, in which the e ect of seasonality has not previously been explored in detail, we nd a larger potential for multiple solution behaviour compared to predator-prey systems. Overall, we show the critical role that seasonality can play in ecological systems.