Meaningful assembly rules should involve some determinism. However, the detection of deterministic processes has been elusive. We know that the trajectory of community assembly is contingent on the species invasion sequence (history). Often, this contingency may lead to different final states, which obscures any specific deterministic process involved. If true, the removal of history’s influence on community formation should reduce the number of final states. We aimed to test this hypothesis by manipulating an invertebrate metacommunity in a group of coastal rock pools. First we mixed the contents of 17 rock pools (including their inhabitants) to construct a Null Community containing all the species.  The Null Community was immediately used for two treatments: (1) 20 plastic beakers were filled with  the Null Community and exposed to the same environmental conditions (on a bench with partial shade) but isolated from invasion by netting and, (2) returning Null Community mixture to the original 17 pools where they were exposed to invasion and different environmental conditions . Five samples were taken from the Null Community as controls and day 0.  Each of the beakers and pools were then sampled on day 11 and 42.

Results/Conclusions

The similarity analyses for the beaker communities revealed that replicates clustered by dates, with the similarity over 85%. These groups where significantly different from one another (Anosim p‹0.001). This indicates that although communities in the beakers changed with time, they did so, following similar trajectories. 4 beaker communities failed to associate with any of the three distinct groups. In contrast to beakers, the experimental pool communities showed no grouping. These results support the importance of history and reveal determinism in the assembly of communities. Yet, it remains unresolved whether the outcome was imposed by environment and/or biological interactions. The fact that the beaker communities were about 15% different indicates a contribution of chance, possibly due do small differences in the initial conditions. In the pools on the other hand, the combination of chance, history, and environment acting at different spatiotemporal scales obscures any deterministic factors.