Assembly history interacts with ecosystem size to influence species diversity

Although species diversity is often correlated with ecosystem size ill a consistent manner, mechanistic explanations of when and why diversity is related to size remain elusive. Rarely considered ill understanding size-diversity relationships is the history of community assembly. I conducted a laboratory microcosm experiment with freshwater protists and rotifers to test for interactive effects of assembly history and ecosystem size oil species diversity. The experiment used a two-way factorial design with four assembly sequences and four ecosystem sizes as treatments. Community dynamics were monitored for about 50-100 generations. The results show that history affected diversity more strongly in smaller ecosystems, presumably owing to greater priority effects. Consequently. history determined when diversity was significantly related to ecosystem size. The results also suggest that long-term transient community dynamics can make assembly history important for community structuring even in the absence of alternative stable states. Because species immigration is essentially stochastic, ecosystem size is variable. and priority effects can be strong in many natural systems, the history X size interaction revealed in this Study also has the potential to shape natural size-diversity patterns.