Species divergence and trait convergence in experimental plant community assembly

TLDR

Despite decades of research, it remains controversial whether ecological communities converge toward a common structure determined by environmental conditions irrespective of assembly history. We experimentally demonstrate that the outcome depends on the level of community organization considered. In a nine‑year grassland experiment, we manipulated initial plant composition on abandoned arable land and then allowed natural colonization. Initial compositional variation kept communities divergent in species identities while they converged in traits, a pattern that cannot be explained by dispersal limitation or neutrality alone and indicates that trait‑based assembly rules and species‑level priority effects jointly drive assembly, making it deterministic yet historically contingent at different organizational levels.

Abstract

Abstract Despite decades of research, it remains controversial whether ecological communities converge towards a common structure determined by environmental conditions irrespective of assembly history. Here, we show experimentally that the answer depends on the level of community organization considered. In a 9‐year grassland experiment, we manipulated initial plant composition on abandoned arable land and subsequently allowed natural colonization. Initial compositional variation caused plant communities to remain divergent in species identities, even though these same communities converged strongly in species traits. This contrast between species divergence and trait convergence could not be explained by dispersal limitation or community neutrality alone. Our results show that the simultaneous operation of trait‐based assembly rules and species‐level priority effects drives community assembly, making it both deterministic and historically contingent, but at different levels of community organization.