Ecosystems are one of the paradigmatic examples in complex systems science. A large number of species interact with each other in various ways, either by feeding upon each other, competing for the same resource, or even collaborating. But within an ecosystem it is not only key to know how the different species that inhabit it are related, there are other factors to be taken into account, such as how they are distributed in space, how they interact with the environment, etc. These factors, among others, determine how an ecosystem will evolve, whether it will remain stable with a nearly constant abundance of each species, or whether, on the contrary, a collapse of the ecosystem occurs possibly reducing biodiversity.
The recently deceased Lord Robert May, one of the fathers of chaos theory and a pioneer in theoretical studies of biology, used a statistical model to show that an increase in the number of species within an ecosystem can lead to a reduction in stability. Large ecosystems, May asserted, are more likely to change when disturbed. A research study, carried out by researchers from the Institute of Cross-disciplinary Physics and Complex Systems (IFISC, UIB- CSIC) and published in Nature Communications, explores the role of dispersion as a destabilizing factor in ecosystems.
An ecosystem can be unstable with respect to factors such as the introduction of new species, species extinction, or environmental changes. May's work, on which this new research is based, focused on the abundance of species for the stability of the ecosystem. The IFISC researchers combined this idea with seminal work by Alan Turing, who showed how dispersion can destabilize a dynamic system. To do this, they started with an ecosystem with species abundances in a homogeneous equilibrium. Starting from such a system, they found the statistical properties that made the system stable and return to the initial state after perturbation. In addition, they added trophic structure that May’s initial model did not contemplate, that is, the existence of predators and prey groups among the species in the ecosystem.
One of the main results of this study is that a stable equilibrium can become unstable once spatial dispersion is introduced into the model. Furthermore, predator-prey relations can act to favour stability. This study opens the door to being able to develop more complex models, for example by adding detailed food-web structure and other features important for the rich and complex dynamics of natural ecosystems.
Baron, J.W., Galla, T. Dispersal-induced instability in complex ecosystems. Nat Commun 11, 6032 (2020). https://doi.org/10.1038/s41467-020-19824-4