Spatial turnover drives bacterial beta diversity in bromeliads tank

Background/Question/Methods

Understanding the patterns and the mechanisms that generate and maintain the biodiversity has been one of the main goals of ecology. The variation in community composition (beta diversity) may be consequence of two different phenomena: the spatial turnover and nestedness. Yet, most previous studies did not distinguish between these two components of beta diversity, which may make interpretation of the processes more difficult. The aim of this study was evaluate which of the main components of beta diversity (spatial turnover or nestedness) drives bacterial community structure. We sampled the bacterial community in six individuals of two bromeliad species (Neoregelia cruenta and Aechmea lingulata) and in four tanks of each bromeliad individual, totalizing 24 tanks per species. The abiotic variables were measured and the bacterial community was sampled in each tank. The bacterial community (16S) was analyzed using the Denaturing Gradient Gel Electrophoresis technique (DGGE). To assess which were the main environmental variables responsible for structuring the bacterial community, we performed a redundancy analysis (RDA). To analyze bacterial composition community similarity between and within bromeliads tanks, we performed an ANOSIM based in Jaccard similarity. Finally, to partition the beta diversity into spatial turnover and nestedness, we performed multiple-sites dissimilarity analysis.

Results/Conclusions

We found 81 Operational Taxonomical Units (OUT) in all bromeliads. The main abiotic variables responsible for structuring the bacterial community were bromeliad diameter, temperature and color explaining 4,7% of the total variation. The bacterial composition did not differ between bromeliad species. The bacterial community was more similar within tanks of the same bromeliads than between tanks of different bromeliads, probably due to a lower dispersal limitation within the same bromeliads and thus homogenizing the bacterial community. Spatial turnover and nestedness were found to contribute differently to beta diversity (beta.SOR = 0.9477). Spatial turnover contributed with 92.20% to beta diversity (beta.SIM = 0.9220), whereas nestedness contributed only with 2.57% (beta.NES = 0.0257). In this way, the beta diversity of bromeliad tanks was explained mainly by spatial turnover. These results indicate that high dispersal rates among the same bromeliad could prevent the action of environmental filters in these local communities.