Seven-year dynamics of testate amoeba communities driven more by stochastic than deterministic processes in two subtropical reservoirs

Testate amoebae are widely distributed in natural ecosystems and play an important role in the material cycle and energy flow. However, community assembly of testate amoebae is not well understood, especially with regard to the relative importance of the stochastic and deterministic processes over time. In this study, we used Illumina high-throughput sequencing to explore the community assembly of testate amoebae from surface waters in two reservoirs of subtropical China over a seven-year period. Majority of testate amoebae belonged to the rare taxa because their relative abundances were typically lower than 0.01% of the total eukaryotic plankton community. The testate amoeba community dynamics exhibited a stronger interannual than seasonal variation in both reservoirs. Further, species richness, rather than species turnover, accounted for the majority of community variation. Environmental variables explained less than 20% of the variation in community composition of testate amoebae, and the community assembly appeared to be strongly driven by stochastic processes. Based on the Sloan neutral community model, it was found that neutral processes explained more than 65% of community variation. More importantly, the Stegen null model analysis showed that the stochastic processes (e.g., ecological drift) explained a significantly higher percentage of community assembly than deterministic processes over seven years, although deterministic processes were more influential in certain years. Our results provide new perspectives for understanding the ecological patterns, processes and mechanisms of testate amoeba communities in freshwater ecosystems at temporal scale, and have important implications for monitoring plankton diversity and protecting drinking-water resources.