Founders Can Increase Determinism of Community Assembly.

The effect of founders (the potential influence of initially colonizing species on the composition, functionality, and stability of communities) plays a crucial role in community assembly; many experimental studies on priority effects or artificially assembled species have suggested the existence of this effect, but direct experimental evidence at the community level remains limited. This study used sterilized and nonsterilized paocai soup (a traditional Chinese fermented vegetable soup) from the same source to simulate initial environments with and without founders. These were placed in beakers with varying opening sizes on an open rooftop for 15 days to explore the impact of founders on community assembly under different dispersal intensities. The 16S rRNA sequencing analysis revealed that communities with founders exhibited lower species richness (320) compared to communities without founders (645). Additionally, communities with founders showed reduced species turnover and richness variation (53.7%) compared to communities without founders (60.9%). Furthermore, the average variability degree (AVD) in communities with founders (0.446 ± 0.044) was significantly lower than in communities without founders (0.927 ± 0.466), indicating higher community stability. Finally, deterministic processes dominated communities with founders (with heterogeneous selection contributing 70%), whereas stochastic processes primarily governed communities without founders (homogeneous dispersal 10% and undominated processes 70%). These findings demonstrate that founders presence reduces dispersal impacts, decreases community diversity, enhances stability, and deterministic processes. The effect of founders fundamentally shapes the direction of community assembly. This study helps further understanding of how founders influence biodiversity maintenance and community assembly processes.