Axel Rossberg

School of Biological and Chemical Sciences, Queen Mary University of London

Structural instability as the key to community ecology

Structural instability denotes situations where small changes in parameters (or external pressures) can fundamentally change the state of a system, in ecological communities typically through extirpations. I will argue based on models and data that structural instability increases with species richness and that natural communities tend to be packed to the point where invasion of any new species leads to extirpation of one other on average. The resulting structural instability gives rise to and explains several phenomena long known to ecologists: model parameterisation is difficult, diffuse indirect interactions are strong, invasions are likely and fast, extirpations (local extinctions) slow, and overall community dynamics spreads over a range of time scales.