Ecological theory suggests that a combination of local species interactions and regional processes, such as dispersal, regulate metacommunity diversity and biomass. On the local scale, in particular initial species composition can greatly determine the compositional fate and functioning of communities. Yet, the relative importance of local compositional versus regional processes over successional time remains understudied. In this study, we used natural benthic microalgae assemblages including their associated bacteria to test the relative importance of local initial microalgae community composition and dispersal on microalgae diversity and biomass regulation in metacommunities. We quantified the factor’s relative importance on local and regional microalgae evenness and biomass, beta-diversity, and the ratio of bacteria to microalgae.
Results/Conclusions
The relative importance of local initial microalgal species composition and dispersal on microalgae evenness and biomass, beta-diversity, and the ratio of bacteria to microalgae substantially changed over time. On the local scale, until the mid-term of the experiment, encompassing approximately 15 microalgae generations, initial community composition largely explained all measured variables while the influence of dispersal was negligible. At the end of the experiment, spanning up to 30 microalgae generations, this changed such that the importance of initial composition declined and dispersal became the predominant explanatory factor for local microalgae biomass, evenness, and the ratio of bacteria to microalgae. Correspondingly, the influence of dispersal on the variables measured on the metacommunity scale also increased over time. Generally, dispersal significantly decreased microalgae evenness, beta-diversity and the ratio of bacteria to microalgae, while it significantly increased microalgae biomass. This suggests that dispersal prevented bacteria from gaining competitive advantage over algae in these metacommunities. The regulation of evenness in these metacommunities largely influenced biomass of the local communities, which highlights the competitive interactions of the different trophic levels. Our study emphasizes the importance of the temporal scale to understand the regulatory role of dispersal on metacommunity structure and functioning.