Draft:Ecological Structural Instability

Ecological Structural Instability refers to the sensitivity of ecological communities to direct or indirect environmental pressures which are so high that they result in species extinctions. . At this point, invasion of a single new species can force the extinction of another. Species of a low abundance with small biomass are the most likely to go extinct at the point of Ecological Structural Instability. If one species replaces the role of another species upon extinction, then this will have little effect on ecosystem function



This links to the mathematical concept of structural instability, defined in dynamical systems theory as a situation where a small change in a system can change its behaviour qualitatively. .

Effects of invaders

Invaders can impact communities directly through:

•	Predation

•	Herbivory

•	Direct interspecific competition between species (e.g. for shelter)

Or indirectly through:

•	Interspecific competition of predators for shared prey.

•	Introduction of a new predator leading to trophic cascades

Near the instability limit, indirect interactions involving multiple species are important, accounting for ~50% of community alterations. The full effects of this would be seen over a long period of time, so short-term responses are a poor measure of the full impact.

Mathematical Models

Mathematical analysis can provide more in depth understanding of ecological structural instability, especially because the effects of indirect interactions can be counter-intuitive, and can be used to make quantitative predictions.

Lotka-Volterra competition models with random interactions aid the study of instability in species-rich communities and are supported by empirical data. Simulation predictions are often robust to variations in model structure, except in some cases

Mathematical analysis shows that around half of invasion attempts succeed, matching observations.