Alternative community compositional and dynamical states: The dual consequences of assembly history

Background/Question/Methods

Much previous work on the ecological consequence of the history of community assembly has focused on the formation of history-induced alternative stable equilibria differing in species composition. However, it is possible that assembly history may simultaneously affect species composition and population dynamics, with communities that differ in composition due to historical differences exhibiting potentially different dynamics.

Results/Conclusions

We tested this hypothesis using a laboratory microcosm experiment in which we manipulated both the colonization order of three bacterivorous protist species in the presence of a protist predator and environmental productivity. Priority effects dominated communities in which two prey species were first colonizers, leading to two different compositional states: one characterized by the dominance of a prey species, the other characterized by the extinction of the same species. No priority effect was observed in communities with a third prey species as the first colonizer, which diverged into the same two compositional states. Communities in the former group exhibited non-cyclic dynamics with the predator attaining low or zero densities, whereas the majority of communities in the latter group exhibited cyclic dynamics driven by the interaction between one prey and the predator, which attained substantial peak densities. As a result, temporal variability of total prey community biovolume also differed among communities with different histories. Productivity altered history effects on community structure and dynamics in some, but not all, assembly history treatments. Our results support the dual (compositional and dynamical) consequences of assembly history and emphasize the importance of incorporating the non-equilibrium view into the field of community assembly.