Strength of species interactions determines biodiversity and stability in microbial communities

Abstract

Organisms -especially microbes -tend to live in complex communities. While some of these ecosystems are very bio-diverse, others aren't 1-3 , and while some are very stable over time others undergo strong temporal fluctuations 4,5 . Despite a long history of research and a plethora of data it is not fully understood what sets biodiversity and stability of ecosystems 6,7 . Theory as well as experiments suggest a connection between species interaction, biodiversity, and stability of ecosystems [8][9][10][11][12][13] , where an increase of ecosystem stability with biodiversity could be observed in several cases 7,9,14 . However, what causes these connections remains unclear. Here we show in microbial ecosystems in the lab that the concentrations of available nutrients can set the strength of interactions between bacteria. At high nutrient concentrations, extensive microbial growth leads to strong chemical modifications of the environment, causing more negative interactions between species. These stronger interactions exclude more species from the community -resulting in a loss of biodiversity. At the same time, these stronger interactions also decrease the stability of the microbial communities, providing a mechanistic link between species interaction, biodiversity and stability.

Transient invaders can induce shifts between alternative stable states of microbial communities

“…S8) exhibiting different species composition. These results are in agreement with recent findings showing that soil communities can relax into alternative community compositions when propagated in laboratory environments (31). We identified two community states that were consistently able to resist low doses of migration from one another ( Fig.…”

Leveraging Experimental Strategies to Capture Different Dimensions of Microbial Interactions

“…Microbes can have net negative, neutral, or positive effect on one another and sometimes qualitative information of directionality may be sufficient to categorize interactions into relationship types and observe patterns ( Yan et al, 2021 ). However, the strength, that is the quantitative magnitude of these effects, can vary and have important implications for the biodiversity and stability of microbial communities ( Ratzke et al, 2020 ). Moreover, considering the strength of the reciprocal relative effect on fitness reveals the more complex nuance of certain types of ecological interactions.…”

Resource-diversity relationships in bacterial communities reflect the network structure of microbial metabolism

“…In order to illuminate how resource number and identity shape the richness of microbiomes, we assayed the assembly of soil-derived bacterial communities in laboratory microcosms (8,12).…”

“…Several mechanisms contribute to the diversity of microbial communities, including the spatial and temporal structure of the environment 12 , dispersal and bacterial motility 13 , warfare 14,15 , and resource-mediated competition and cooperation [16][17][18] . With respect to resources, ecological theory has mostly focused on the effect of the number of available resources on community diversity rather than their identity 19 .…”