New study demonstrates coalition breakdown in microbial ecosystems

Government coalitions often dissolve when too many parties disagree on too many issues. Even if a coalition seems stable for a while, a small crisis can cause a chain reaction that eventually causes the system to collapse.

A study carried out at the Department of Physics of Bar-Ilan University demonstrates that this principle also applies to ecosystems, in particular bacterial ecosystems.

In an ecosystem, different species can negatively affect each other. The cheetah, for example, preys on zebras, and jungle trees compete for sunlight. Conversely, species can influence each other positively, such as the bee pollinating flowers. In the 1970s, the famous mathematician and biologist Robert May predicted the collapse of coalitions in ecosystems, such as trees in tropical forests, animals in savannahs or fish in coral reefs. According to May, an ecosystem can become unstable and collapse if it contains too many species, or if the networks of connections between them are too intense. In other words, according to May’s theory, small ecosystems in nature are generally characterized by strong ties, while large systems are characterized by weak ties. Until now, May’s theory has been difficult to prove due to the difficulty of measuring these networks.

In the new study published in Nature ecology and evolutionYogev Yonatan and Guy Amit from the research group of Dr. Amir Bashan of the Department of Physics at Bar-Ilan University, in collaboration with Dr. Yonatan Friedman of Hebrew University, demonstrated the first proof of May’s theory in the microbial ecosystems.

The microbiome is of great importance to our health – such as the digestion and absorption of nutrients and the formation of our immune system. Disturbances in the ecological balance are associated with numerous adverse effects on our physical and mental well-being, from obesity to various mental and psychiatric disorders, including the risk of chronic diseases such as diabetes and cancer. Certain interventions have been introduced to maintain a healthy balance, including dietary elements, probiotic intake, antibiotics, and fecal transplantation. Outside the human body, bacteria play a vital role in creating the living conditions for larger organisms. They are necessary for the breakdown of nutrients, regulating the production and breakdown of gases in the atmosphere, including greenhouse gases, methane, carbon dioxide, etc..

Researchers have developed a new computational method that can estimate the level of connectivity in the ecosystem (a measure of the number of connections in the network and their strength) by analyzing large amounts of data from a variety of microbial communities without having to create a detailed map of all interactions – analogous to how the temperature of a glass of water can be measured without full knowledge of the velocity and position of each water molecule.

First, the researchers tested the new method on simulated ecological dynamics data. Later, they analyzed data from thousands of samples of bacterial populations from various organs in the human body and from bacterial populations that live on sea sponges in coral reefs at various sites around the world. In each ecological environment, they compared the number of different species in the bacterial population and the level of connectivity of the ecological network, and found the first evidence for the existence of Robert May’s principle of stability in these systems.

Understanding the principles of bacterial community stability is important for two reasons. Principles of stability are the rules of the game that dictate ecosystem evolution in a particular environment and help answer scientific questions such as why different bacterial populations grow in different places or why the number of species differs in different places. place to place. A second reason is that ecosystems can collapse as a result of disruption of the ecological balance as a result of human intervention. This is true of coral reefs in Australia and rainforests in Brazil, and it is also true of bacterial populations in humans and in the environment. It is important to assess how close these systems are to collapse so that we know how to avoid damaging them and how they can be rehabilitated.

The results show that the number of different species of bacteria that can survive in the same ecological environment is limited by the strength of the interactions between them. For example, in the gut, where there is an abundance of food for bacteria and less intense competition for resources, we find tens to hundreds of different types of bacteria. The reverse happens in other places where competition is fierce and the number of species is low. Understanding the principles of bacterial population stability is particularly important when we are concerned with the development of treatments that include attempts to influence, modify and control their composition. Therefore, understanding the ecological laws that govern bacterial populations in humans and around the world is very important both for the development of medical treatments and for the preservation of the environment.

The subject of this research, which is typically studied by researchers in the life sciences, is an example of a growing trend in recent years towards multidisciplinary research, in which complex issues are explored by experts from various disciplines. In this study, physicists used tools from the fields of statistical physics, nonlinear dynamics, network science, and data science to study problems characterized by large amounts of data, including networks in bacterial populations or various human interactions are only part of it.


Journal reference:

Yonatan, Y. et al. (2022) Complexity-stability trade-off in empirical microbial ecosystems. Nature ecology and evolution.