Recent developments in metacommunity ecology have shown that predator dispersal can lead to increased stability of trophic interactions and thus affect the diversity, composition, and function of prey communities. However, this effect may depend on the identity and arrival time of predators during the assembly of prey communities. Here we test the hypothesis that variation in dispersal mechanisms across bacterivorous protozoa affects their arrival sequence, and thus the diversity, composition and function of bacterial communities in pitcher plants. In purple pitcher plant (Sarracenia purpurea) leaves, bacterial decomposers are consumed by various species of protozoan a simple aquatic food web. Protozoa colonize soon after new leaves open and undergo a predictable succession that ends when old leaves senesce. We conducted a field experiment in which we monitored the community within a newly opened focal leaf, after manipulating the species composition of the surrounding older leaves. Surrounding leaves were sterilized, then inoculated with a small flagellate (Poterioochromonas sp.), a ciliate (Tetrahymena sp.), or a culture with no protozoans. We compared these treatments with leaves in which surrounding leaves were unmanipulated. After 30 days, we counted protozoans from all leaves and profiled the bacterial community by targeting 16S sequences using the MiSeq Illumina platform. We expected the small Poterioochromonas sp. to have a dispersal advantage over the larger Tetrahymenasp., resulting in distinct protozoan assembly sequences with consequences for bacterial diversity and function.
Results/Conclusions
We found increased Poterioochromonas sp. dispersal and persistence in new leaves relative to Tetrahymena sp. Other species of protozoa (Colpoda sp., and unidentified protozoa), mites and rotifers (Habrotrocha rosa) also colonized target leaves from surrounding natural sources, but we only found potential interactions between Poterioochromonas sp. and rotifers. Bacterial communities were significantly affected by the protozoan dispersal treatment. In particular, we found that the arrival time of Poterioochromonas sp. influenced bacterial composition. We used the bioinformatics tool of PICRUSt to estimate the functional profile of these bacterial communities. Bacterial function was primarily associated with across-membrane transport, chemotaxis and quorum sensing. Bacterial function was only marginally affected by the abundance of Poterioochromonas sp., but not affected by Tetrahymena or other bacterivores. These results provide evidence of distinct dispersal patterns in predators altering the prey community composition in a natural metacommunity system. Importantly, our findings highlight the need to recognize dispersal mechanisms that result in different colonization and persistence rates and have consequences for trophic structure and stability.