Nature is full of cooperative relationships: plants that benefit from fungi or insects, microbes that help each other grow, or even human groups working together. However, competition for resources is often emphasized as the main force driving interactions within these communities.

In a new study, a research team led by the  Institute of Evolutionary Biology (IBE), a joint centre of the Spanish National Research Council (CSIC) and the Pompeu Fabra University (UPF), has developed a comprehensive mathematical theory in which, for the first time, cooperation plays an essential role in explaining how ecosystems are organized and maintained.

The new model provides a framework for studying how cooperation can become a driver of biodiversity and resilience in all types of ecological environments. “This new theory proposes that cooperative interactions promote diversity beyond traditional models purely based on competition”, notes Ricard Solé, head of the study, principal investigator of the IBE (CSIC-UPF), and ICREA professor and researcher in the Department of Medicine and Life Sciences at UPF.

The proposal is inspired by neutral ecological theory, a framework that assumes all species in an ecosystem are, on average, equivalent. Under these conditions, the new theory reveals the emergence of a cooperative core, a set of species that maintain high abundance and longevity in the ecosystem while helping each other.

Published in PNAS, the study provides a new paradigm for understanding the maintenance of diversity in complex ecosystems, with key implications for the microbiome, synthetic biology, and the origin of life.

A cooperative species core sustained over time

The major novelty of the study is that it incorporates a key element often absent from these models: cooperation between species as an essential component for successful reproduction. “Our model proposes that cooperation can be an essential process for the maintenance of ecosystems,” says Artemy Kolchinsky, co-first author of the study and postdoctoral researcher in Solé’s Complex Systems group.

The new theory starts from the premise that no species has an inherent advantage over others. It also relies on the minimum number of variables and processes to explain the evolution of ecosystems over time. “The model allows us to study global biodiversity patterns based solely on random processes of birth, death, and migration, with two independent variables: the number of individuals in the group and the species migration rate,” adds Jordi Piñero, co-first author of the study and postdoctoral researcher at Michigan State University.

Although the theory can explain all possible regimes within an ecosystem, the most surprising result emerges when species migration is low. “In this case, the model predicts that the abundances of different species are distributed into two very distinct groups”, says Solé, also external professor of the Santa Fe Institute. “On the one hand, there are many rare species; on the other, a small but stable set of very abundant species”.

According to the study, this second group forms a cooperative core, a set of species that rely on each other to thrive and, in doing so, create the conditions to sustain a wide range of low-abundance species. This core does not disappear even when migration is very limited and acts as a driver of ecological diversity and stability. “When migration is high, the model recovers the classical results of theory based exclusively on competition,” adds Solé.

Cooperation to rethink the links sustaining the microbiome or explaining the origin of life

The new theoretical framework could broaden our perspective on ecological relationships and inspire cooperation-based synthetic biology solutions. “Our model could help design cooperative microbial consortia that are more stable, with a core of resilient species”, says Piñero.

Moreover, the team points to a revision of the origin of life through the lens of cooperation. “The new model provides a theoretical framework to explore how the first self-replicating molecules might have required cooperation to establish long-lasting living systems”, adds Kolchinsky.

In the future, the research team hopes to use synthetic biology to test the scope of the predictions of the new theory. “The new model offers us a unified framework to study how cooperation, as essential as competition, can become a driver of biodiversity and resilience in all types of ecosystems,” concludes Solé.

Article referenciat:  Piñero, J., Kolchinsky, A., Redner, S. & Solé, R. (2025). Neutral theory of cooperative dynamics. Proceedings of the National Academy of Sciences of the United States of America, 122(51), e2515423122. https://www.pnas.org/doi/10.1073/pnas.2515423122