Empirically it is observed that many stable ecosystems are characterized by a complex structure, namely a large number of species, each of which with many predator-prey interactions. Typical examples are the rain forests or the coral reefs. On the other hand the theoretical physicist Robert May in the 70 and 80 investigated the relationship between complexity and stability in ecological communities, with a model that describes a general ecosystem as a food-web, concludes that the stability of an ecosystem decreases as the number of species and interactions.
Recently, a study conducted by the group of statistical physics of University of Granada (Spain) has identified a new statistical properties of ecological networks, easily measurable, which contemplates at the same time large number of species, complexity and stability: the trophic coherence ( “that concerns nutrition “, derivative of Greek τροφή” nourishment “). This is a measure of how species are placed neatly in the food pyramid in distinct well-defined and separate layers.
By analysing a database of nearly 50 real food webs, they found a strong correlation between the stability of networks and their trophic coherence, much more prominent than that present between network complexity and stability, indicating a new path for the solution of the paradox of May.