Correlation, selection and the evolution of species networks

We use a generalised version of the individual-based Tangled Nature model of evolutionary ecology to study the relationship between ecosystem structure and evolutionary history. Our evolved model ecosystems typically exhibit interaction networks with exponential degree distributions and an inverse dependence between connectance and species richness. We use a simplified network evolution model to demonstrate that the observed degree distributions can occur as a consequence of partial correlations in the inheritance process. Further to this, in the limit of low connectance and maximal correlation, distributions of power-law form, P(k)∝1/kP(k)∝1/k, can be achieved. We also show that a hyperbolic relationship between connectance and species richness, C∼1/DC∼1/D can arise as a consequence of probabilistic constraints on the evolutionary search process.