Succession comprises a sequence of threshold-induced community assembly processes towards multidiversity

Research on ecological successions and community assembly shaped our understanding of community establishment, co-existence, and diversity. Although both lines of research address the same processes such as dispersal, species sorting, and biotic interactions, they lack unifying concepts. However, recent theoretical advances proposed to integrate both research lines and thus provided hypotheses on how communities assemble over time and form complex ecological systems. This framework predicts a sequence of stochastic and niche-based processes along successional gradients. Shifts in these assembly processes are assumed to occur abruptly once abiotic and biotic factors dominate over dispersal as main driver of community assembly. Considering the multidiversity composed of five organismal groups including plants, animals, and microbes, we empirically show that stochastic dispersal-dominated community assembly is replaced by environmental filters and biotic interactions after around 60 years of succession in a glacier forefield. The niche-based character of later successional processes is further supported by a pronounced decline in multi-beta-diversity after the shift in assembly processes. Our results support recent theories and provide new insights into the emergence of multidiverse and complex ecosystems. Our study will stimulate updates of concepts of community assembly considering multiple taxa with unique and complementary ecological roles and help to bridge the gap between research on successions and community assembly.