Fig. 2

Summary of the proposed methodology. Starting from a regional pool of species (top), the immigration rate (turnover high or low) and the environmental filtering determine the species that can be observed. The environment may be homogeneous (coloured rectangles), heterogeneous (triangles), or may be shaped by continuous transformations due to strong feedbacks with the microbial activity (cyclic arrows). Sampling these environments, classifying the samples into classes, and performing neutrality tests will lead to a classification of environments into different types of niches