Combined in situexperimentation and modelling approaches to disentangle processes involved in the earliest stage of community assembly

The ecological process of community assembly is described as the succession of three phases: colonization, regulation and segregation. Early colonization remains the least studied and quantified phase of assembly. In order to fill this gap, an approach combining in situexperiments and modelling was proposed to study colonization by a benthic macrofauna community in open microcosms containing a single, non-limiting resource. The experiment was three months long. A total of 51 taxa were observed in the microcosms, but data analyses of the species composition and abundances revealed that five species, Capitellaspp., Gammaropsis maculata, Erichtionus punctatus, Nereiphylla parettiand Harmothoe mariannae, explained most of the observed variation in the assembly process. The population dynamics of these species were simulated taking into account functional traits that govern individual interactions. The dynamic model simulated a demographic stochasticity due to low population densities that result from the small size of the experimental microcosms. Using this combined approach of experiments and modelling, we showed that predation interactions alone can account for the abundances and species composition of primary consumers during the transient phase of early colonization.