Stable or chaos?

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The degree of biodiversity and the strength of interactions between species can
The degree of biodiversity and the strength of interactions between species can be used to predict whether or not an ecosystem will remain stable. Photo: pixabay

Researchers discover key to predicting the future of ecosystems

Whether in the gut, in the lake, in the forest or in the meadow: All over nature, a wide variety of living organisms form ecosystems. How these develop is a question that is extremely relevant in both medicine and environmental protection. An international team of researchers, including Daniel Rodriguez Amor from the University of Graz, has succeeded in finding an answer to this question in the laboratory: "Only two factors - the number of species and the average intensity of interaction between them - determine whether an ecosystem remains stable or not," Rodriguez Amor summarizes the result of the study, which was published in the renowned scientific journal Science.

Researching the dynamics of ecosystems is difficult because it is almost impossible to conduct controlled experiments in nature. Targeted interventions could have unforeseeable consequences. For this reason, scientists led by physicist Jeff Gore at the Massachusetts Institute of Technology (MIT) in the USA are studying the interactions between species using bacteria in the laboratory. We have formed differently composed communities of two to 48 microbial species and observed how they develop under different conditions," reports biophysicist Daniel Rodriguez Amor, who conducts research at the University of Graz in the field of excellence "COLIBRI - Complexity of Life in Basic Research and Innovation. As a postdoc, he was at MIT and worked on the study.

Diversity and interaction
In the first phase, the population of each species was stable. Then, the researchers gradually increased the complexity of the communities by adding more species and/or intensifying the strength of the interactions between species by increasing the nutrient concentration in the environment. If the number of species and/or their interactions exceed a certain threshold, the system abruptly enters a new phase in which some species begin to die out but the populations of those that remain are stable," Rodriguez Amor explains. If more species are added and/or the intensity of their interactions continues to increase, the transition to phase three occurs: "The populations of individual species begin to fluctuate wildly. This is an indication that the ecosystem has lost stability," says the biophysicist. With their experiments, supported by a mathematical model, the researchers were able to show that the phase transitions can be predicted solely by the species diversity in the community and the strength of the interactions between the species.

From the laboratory to nature
The extent to which these results are also valid in the wild now needs further research. There are indications of this: "In lakes, for example, the increase in nutrient concentration due to fertilizers from agriculture can lead to a bloom of cyanobacteria. These consume oxygen, which can lead to the extinction of many species. According to our model, we might need to limit nutrient inputs to keep the intensity of interactions low and allow stable coexistence of species," Rodriguez Amor says.

Emergent phases of ecological diversity and dynamics mapped in microcosms Jiliang Hu, Daniel R. Amor, Matthieu Barbier, Guy Bunin, Jeff Gore Science, 6 Oct 2022, Vol 378, Issue 6615, pp. 85-89.­1126/scien­ce.abm7841

Gudrun Pichler