It is one of the greatest tasks in ecological research to explain species co-occurrence patterns in plant communities by fundamental assembly rules. Real communities contain fewer species combinations than expected by chance and existing combinations resist invaders turning them into “forbidden”, never co-occurring combinations. Forbidden combinations refer to species not sharing similar realised niches although fundamental niches are similar. Some argue that the mechanism behind these assembly rules is competitive exclusion, while others argue for guild proportionality or habitat heterogeneity. Non-random species combinations can even be generated from random birth, death and dispersal processes in a metacommunity.
The assembly processes of local communities can be considered as filters at the local and regional scale to select community members from the broader species pool.
At the local scale community assembly can depend on the sequence in which species establish in a community arising from competitive hierarchies between entering species and species in the resident community. They can either mean rejection, coexistence or dominance of the entering species and in case of the latter alteration of the resident community.
To analyse the relevance of individual plant functional traits linked to these competition processes is one of the key objectives of ASSEMBLE. Particularly, the analysis of trade-offs between allocation towards stronger dominance and higher fecundity will increase understanding and prediction of sequence effects in local community assembly.
In a landscape perspective sequence effects in the exchange of individuals of different species between local communities, create metacommunities with alternative local community composition. In comparison with functional traits important at the local scale, the question is how dispersal traits such as terminal velocity, seed number, seed appendices trade off with traits associated to competition or regeneration.
In the end, understanding the interplay between trait composition of extant communities, traits of entering species and spatiotemporal metacommunity configuration will deliver an important tool for predicting functional biodiversity.