[SS27] Dynamics and Structures of Biological Networks III: Ecological Networks and Intercellular Traffic Networks

[SS27-04] Emergent behaviors in complex microbial ecosystems

*Jiliang Hu¹ (1. X-Institute, Tsinghua University (China))

Keywords:

microbial ecology,diversity,stability,invasibility,emergent behavior

From tropical forests to gut microbiomes, ecological communities harbor diverse and abundant species. Understanding the complex emergent phenomena of diversity, stability, and invasibility in these communities within a unified framework has been a significant challenge. We address this knowledge gap by bridging experiment and theory showing that simple community-level features govern emergent behaviors. By utilizing bacterial microcosms, we demonstrate that as the number of species or the strength of interactions increases, microbial ecosystems transition through three distinct dynamical phases: from stable coexistence, to partial coexistence, to the emergence of persistent fluctuations and alternative stable states in species abundances, confirming theoretical predictions. Notably, high biodiversity and dynamic fluctuations reinforce each other under fixed conditions. Invasions of microbial communities by species such as pathogens can have significant impacts on ecosystem services and human health. Predicting the outcomes of these invasions, however, remains a challenge. Here we show that the interplay between dynamics, interaction strength, and diversity determine the invasion outcome in microbial communities. We found that the communities with fluctuations in species abundance are both more invasible and more diverse than stable communities, leading to a positive diversity-invasibility relationship among communities assembled in the same environment. As predicted by theory, increasing interspecies interaction strength and species pool size leads to a decrease of invasion probability in our experiment. Although diversity-invasibility relationships are qualitatively different depending upon how the diversity is changed, we provide a unified perspective on the diversity-invasibility debate by showing a universal positive correspondence between invasibility and survival fraction of resident species across all conditions. Communities composed of strongly interacting species can exhibit an emergent priority effect in which invader species are less likely to colonize than species in the original pool. However, in this regime of strong interspecies interactions, if an invasion is successful, it causes larger ecological effects on the resident community than when interactions are weak. Overall, my work uncovers predictable emergent patterns of diversity, dynamics, and invasibility in ecological communities, offering insights into a unified framework for microbial ecology.