Drivers of population cycles in ecological systems
Abstract
In this thesis, mathematical models are used to investigate potential drivers of population
cycles. Population cycles are a common ecological phenomenon, yet the
mechanisms underpinning these oscillations are not always known. We focus on two
distinct systems, and evaluate potential causes of cyclic dynamics.
In the first part of the thesis, we develop and analyse a host–pathogen model,
incorporating density-dependent prophylaxis (DDP). DDP describes when individuals
invest more in immunity at high population densities, due to the increased risk
of becoming infected by a pathogen. The implications of this for the population
dynamics of both host and pathogen are examined. We find that the delay in the
onset of DDP is critical in determining whether DDP increases or decreases the
likelihood of population cycles.
Secondly, we focus on a particular cyclic vole population, that of Kielder Forest,
Northern UK. We construct a model to test the hypothesis that the population
oscillations observed in this location are caused by the interaction between the voles
and the silica in the grass they consume. We extend our model by including seasonal
forcing, and study the effects of this on the population dynamics.