Interactions between frequency and size of disturbance affect competitive outcomes

Disturbance has many effects on ecological communities, and it is often suggested that disturbance can affect species diversity by altering competitive outcomes. However, disturbance regimes have many distinct aspects that may act, and interact, to influence species diversity. While there are many theoretical models of disturbance-prone communities, few have specifically documented how interactions between different aspects of a disturbance regime change competitive outcomes. Here, we present a model of two plant species subject to disturbance which we then use to examine species coexistence over varying levels of two aspects of disturbance: frequency, and spatial extent (i.e., area disturbed). We show that the competitive outcome is affected differently by changes in each aspect and that the effect of disturbance frequency on species coexistence depends strongly on the spatial extent of the disturbance, and vice versa. We classify the nature of these interactions between disturbance frequency and extent on the basis of the shape of the resulting coexistence regions in a frequency-extent parameter plane. Our results illustrate that different types of interaction can result from differences in life-history traits that control species-specific sensitivity to frequency and extent of disturbance. Thus, our analysis shows that the various aspects of disturbance must be carefully considered in concert with the life-history traits of the community members in order to assess the consequences of disturbance.