Bouvier T., Venail P., Pommier T.,Bouvier C., Barbera C., and Mouquet N. (2012).

PLoS ONE, 7, e37620, doi:10.1371/journal.pone.0037620

Key message :Despite its importance in the context of global change by human activities, empirical evidence for ecological insurance remains scarce and controversial. Here we use natural aquatic bacterial communities to explore some of the predictions of the spatial and temporal aspects of the ecological insurance hypothesis. Addressing ecological insurance with bacterioplankton is of strong relevance given their central role in fundamental ecosystem processes. Our experimental set up consisted of water and bacterioplankton communities from two contrasting coastal lagoons. In order to mimic environmental fluctuations, the bacterioplankton community from one lagoon was successively transferred between tanks containing water from each of the two lagoons. We manipulated initial bacterial diversity for experimental communities and immigration during the experiment. We found that the abundance and production of bacterioplankton communities was higher and more stable (lower temporal variance) for treatments with high initial bacterial diversity. Immigration was only marginally beneficial to bacterial communities, probably because microbial communities operate at different time scales compared to the frequency of perturbation selected in this study, and of their intrinsic high physiologic plasticity. Such local physiological insurance may have a strong significance for the maintenance of bacterial abundance and production in the face of environmental perturbations.

Illustration of the diffusion chambers and experimental design of the experiment carried out in this study. A) The 2-L capacity diffusion chambers used in this study. B) A diffusion chamber consists of a 120 mm diameter PlexiglasH cylinder (1), with 0.22 mm pore size polycarbonate membranes at both ends (2) allowing ample percolation of water and dissolved substances (grey arrows). The thin membrane is protected by a Plexiglas protection (3). Sampling was done by opening the cap of the chamber (4). Rubber seals were used for water-tightness. C) The bacterial community from the Thau lagoon was incubated within the diffusion chambers. After a 48 h period of acclimation in Thau lagoon water, the bacterioplankton were transferred successively in their chambers between the Bagnas water tank and the Thau water tank every 48 hours. This resulted in bacterial communities experiencing each environment twice. Each chamber was sampled nine times during the experiment (black triangles). Three different levels of diversity and dispersal rates were tested (High, Medium, and Low diversity, and 0%, 1% and 10% of immigration, respectively; see Methods).

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OTHER TOPICS: Aesthetics of Biodiversity, Biodiversity & Ecosystem Functioning, Biogeography, Macroecology & Ecophylogenetics, Experimental Evolution, Functional Biogeography, Functional Rarity, Metacommunities, Metaecosystems, Reviews and Synthesis, Trophic Biogeography & Metaweb