Breaking the Spell of Nestedness: a scientific paper explores the entropic origin of nestedness in mutualistic systems

Mutualistic interactions, those that are naturally beneficial for both interacting species, are recurrently found in ecosystems. Observations of natural systems show that if we draw mutualistic relationships as links between species, the resulting mutualistic network of interactions displays a widespread particular ordering called nestedness. In such an ordering, the mutualistic partners of a given species conform a subset of the partners of all species with larger degree, that is, of those species having more interactions.

On the other hand, theoretical works show that a nested structure has a positive impact on a number of relevant features of mutualistic communities ranging from species coexistence to structural stability and biodiversity. However, how nestedness emerges and what are its determinants, are still open challenges that have led to multiple debates to date. In a new paper  published in Physical Review X, an international team of scientists including ISI Foundation Research Leader Yamir Moreno shows, by applying a statistical mechanics' theoretical approach to the analysis of 167 real mutualistic networks, that nestedness is not an irreducibly macroscopic feature but an entropic consequence of the degree sequences (number of mutualistic interactions of each species).

Researchers find that an outstanding majority of the analyzed networks does not show statistically significant nestedness. These findings point to the need of revising previous claims about the role of nestedness and might contribute to expand our understanding of how evolution shapes mutualistic interactions and communities by placing the focus on the node-dependent properties rather than on global quantities. Besides, given that nested patterns have been identified in networks of social and economic interactions as well, scientists suggest that results may be useful in many fields beyond ecology.

“Breaking the Spell of Nestedness: The Entropic Origin of Nestedness in Mutualistic Systems”, Clàudia Payrató-Borràs, Laura Hernández, and Yamir Moreno. Pyshical Review X, 13th August 2019. Link