Directionality and community‐level selection 

Guy Bunin, 2021.

Many ecological community dynamics display some degree of directionality, known as succession patterns. But complex interaction networks frequently tend to non‐directional dynamics such as chaos, unless additional structures or mechanisms impose some form of, often fragile or shot‐lived, directionality. We exhibit here a novel property of emergent long‐lasting directionality in competitive communities, which relies on very minimal assumptions.

We model communities where each species has a few strong competitive interactions, and many weak ones. We find that, at high enough diversity, the dynamics become directional, meaning that the community state can be characterized by a function that increases in time, which we call ‘maturity'. In the presence of noise, the community composition changes toward increasingly stable and productive states. This scenario occupies a middle ground between deterministic succession and purely random species associations: there are many overlapping stable states, with stochastic transitions, that are nevertheless biased in a particular direction. When a spatial dimension is added in the form of a meta‐community, higher‐maturity community states are able to expand in space, replacing others by (exact or approximate) copies of themselves. This leads to community‐level selection, with the same maturity function acting as fitness. Classic concepts from evolutionary dynamics provide a powerful analogy to understand this strictly ecological, community‐level phenomenon of emergent directionality.

https://onlinelibrary.wiley.com/doi/10.1111/oik.07214

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