Constraints on the distribution of species abundances indicate universal mechanisms of community assembly

Recently, a 2018 study by Ulrich et al. introduced the Weibull distribution as a flexible approach to model the distribution of species abundances in ecological communities. They pointed to possible limitations in the realized parameter spaces of this distribution as possibly indicating ecological constraints on species abundances. Here, we explore this question in detail using three large global data sets on quantitatively assessed plant, invertebrate, and vertebrate communities. By fitting the Weibull distribution to these communities, we confirm that only a minor amount of the possible ranges in the scale and the shape parameters of the Weibull distribution are realized. Shapes of distributions become more similar across taxa with increasing species richness and average abundances. This finding points to stochastic explanations for species abundance shapes, possibly linked to local colonization and extinction dynamics. We introduce the Weibull survival time parameter as a way to define the proportion of rare species in a community. This proportion increased with increasing species richness.Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Science; National Science Center, Poland (UMO-2017/27/B/NZ8/00316)