Self-organisation of ecosystem engineers on different time scales

Abstract

Ecosystem engineers are organisms that influence the availability of resources by shaping their environment. The presence of vegetation in drylands, for example, increases the infiltration of water in the soil. Combined with a long-range competition for water, this can result in pattern formation - a form of self-organisation that can be associated with ecosystem resilience. Such organisation might take time, and the engineered construct - in this case the soil - might respond more slowly than the engineer itself. Wondering what this would mean for ecosystem resilience, we modelled self-organising ecosystem engineers by extending an existing reaction-diffusion model for vegetation in drylands, to include the engineered construct and the time scale at which it changes. In short, our extended model predicts a duality in the resilience of ecosystem engineers with a slowly changing engineered construct. If external conditions change more slowly than the construct, patterns form, and resilience can be found in adaptability. If external conditions change faster than the construct, the ecosystem shows resilience in the form of robustness: the ecosystem can survive and bounce back from more extreme conditions. On a more general note, the results are an example of how increased rates can under the right circumstances prevent behavioural change through bifurcations.