Temperature- and dispersal-dependent priority effects in aquatic bacterial communities

The immigration history of communities, i.e. the timing of the arrival of species to an ecological community, can profoundly affect community composition through a process known as priority effects. Warming could possibly enhance priority effects by increasing growth rates of early arriving species, whereas high dispersal rates of better adapted immigrants should dampen it. Here we implemented a full-factorial experiment where both temperature (15, 20 and 25°C) and dispersal rates (0, 5 and 20% cell exchange from an external dispersal source) we manipulate to test their interactive effects on the importance of priority effects in the assembly of aquatic bacterial communities. We found that the likelihood for priority effects was the lower the higher the dispersal rates were as a consequence of successful colonization of migrant bacteria. On the other hand, warming could strengthen priority effects, and in parallel, decrease the colonization success of immigrants. Interestingly, some immigrants (i.e. Algoriphagus) could successfully outcompete founder taxa of already established communities, whereas others (Limnohabitans, the hgcI clade and Novosphingobium) were less successful. Additionally, warming could reduce the establishment success of migrants that are successful at lower temperature (e.g. Loktanella, Roseibacterium), prompting the temperature-dependency of priority effects. Consequently, the strength of priority effects may be not merely influenced by the effect of warming and dispersal rates of immigrants, but the composition of both dispersed and invaded bacterial communities.