Abstract
New microbial communities often arise through the mixing of two or more separately assembled parent communities, a phenomenon that has been termed “community coalescence”. Understanding which features of complex parent communities determine the outcomes of any given coalescence event is an important challenge. While recent work has begun to elucidate the role of competition in coalescence, the effect of specific underlying structures of interactions remains unclear, and that of cooperation, a key interaction type commonly seen in microbial communities, is still largely unknown. Here, using a general consumer-resource model we study the combined effects of competitive and cooperative interactions on the outcomes of coalescence events. We simulate coalescence between pairs of communities lying on the spectrum from competition for shared carbon resources, to cooperation through cross-feeding on leaked metabolic by-products (facilitation). Specifically, we develop novel metrics to quantify community-wide competition and cooperation levels, and show that these can predict which community dominates in pairwise coalescence events. We find that when both types of interactions are present in the parent communities, the less competitive one, which maximizes resource partitioning, contributes a higher proportion of species to the new community after coalescence, regardless of its cooperativeness. However, counter-intuitively, when competition in both parent communities is significantly weaker than facilitation, the more cooperative one is at a disadvantage during coalescence because multi-species invasions are able to disrupt established cross-feeding links. Encounters between microbial communities are becoming increasingly frequent across the globe, and there is great interest in how the coalescence of microbial communities affects environmental and human health. Our study provides new insights into the mechanisms behind microbial community coalescence, and a framework to predict outcomes based on the interaction structures of parent communities.
Author summary In nature, new microbial communities often arise from the fusion of whole, previously separated communities (community coalescence). Despite the crucial role that the interactions among microbial communities can play in ecosystems, our ability to predict the outcomes of coalescence events remains limited. Here, using a general mathematical model, we study whether and how the structure of species interactions confers an advantage upon a microbial community when it encounters another. We find that when both competition and cooperation are present, less competitive communities, which partition resources well, dominate in coalescence events. However, when competition is negligible, cooperation turns out to be detrimental to coalescence success, because highly cooperative communities are more susceptible to multi-species invasions. There are many potential environmental and health implications of microbial community coalescence, which will benefit from the theoretical insights that we offer here about the fundamental mechanisms underlying this phenomenon.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Submitted version