Complex systems are systems with many components that can interact with each other. They are difficult to understand due to different types of interactions and relationships. Microbial communities in nature can contain thousands of microbial species and are an example of a complex system in biology. These microbial communities are driven by complex multi-species interactions but also interactions of species or sub-communities with the environment.

In microbial ecology, concepts that are able to describe the state of microbial communities are useful to compare communities of different origin and help interpret the community development and evolution. One concept that tries to describe complex system development is the adaptive cycle by Gunderson and Hollings (2002). It divides the evolution of systems into four major phases (exploitation, conservation, release, reorganization) by the interplay of three essential variables (connectedness, resilience and potential).

Here, we propose that the adaptive cycle is a valuable tool to study the state of microbial communities in developing soil. We applied this method on bacterial, archaeal and eukaryotic microbial community data of a glacier transect in East-Antarctica (Larsemann Hills) and found the results to match the expected developmental state of the soil.

The communities of "older" soils, that are expected to be more developed, show a higher resilience and more connectedness. In addition, our results are more robust when the combination of eukaryotic and prokaryotic microbial community data is used. Prokaryotic communities alone are less informative, probably because some prokaryotes show a much higher potential to be the absolute early pioneers and are able to live on their own with only few inter-species interactions to the environment. To sum up, the adaptive cycle can be a tool to describe developments of microbial communities in natural ecosystems.