How is diversity maintained in an exceptionally rich community? the roles of temporal variability, spatial heterogeneity and interactions

Coexistence theory remains largely untested in the field, which is essential to understand diversity maintenance in nature. We have assessed coexistence mechanisms in a species-rich grassland. The storage effect, where species profit from favorable periods and persist when conditions benefit others, is irrelevant, while the relatively ignored mechanism of temporal relative non-linearity was more important. Time-independent mechanisms are far more influential. There are alliances of species that perform better together by collectively outcompeting other species, despite competing between themselves. Different alliances dominate microsites differing in water-stress, enhancing community diversity. This may be driven by plant interactions mediated by soil biota, which stabilize coexistence within subsets of species that change over the hydric-stress gradient. How such stable subsets maintain community-wide diversity is still unknown.