Abstract
We conducted a metacommunity experiment to investigate the role of dispersal for bacterial community composition (BCC) and function of freshwater bacteria. Bacteria were dispersed from a common source pool into three different lake communities in their natural lake water. The experiment was conducted in dialysis bags to enable a decoupling between a change in the local environment and dispersal. BCC was determined by terminal restriction fragment length polymorphism (tRFLP) of the 16S rRNA gene. We show that the greatest changes in BCC occurred between 10% and 43% of dispersal of standing stock per day. Functioning, measured as growth rate, was also affected by dispersal in all three communities but the qualitative pattern differed between communities, sometimes showing a hump-shaped relationship to dispersal and sometimes decreasing with increasing dispersal. In all waters, functioning was related to BCC. Our results show that dispersal does affect BCC and functioning but that high dispersal rates are needed. Further, the effect of dispersal on BCC and function seem to depend on the quality of the habitat to which bacteria disperse into.
Highlights
Due to the concern of which consequences the loss of biodiversity will have on ecosystems, it is of considerable interest to evaluate the importance of biodiversity for ecosystem functions (e.g. [1,2])
The non-metric multidimensional scaling (NMDS) analysis showed that communities exposed to the lowest dispersal rates as well as the inoculum/start communities were most dissimilar from another, while communities receiving the highest dispersal (43 and 70% per day) showed greater similarity to each other (Fig. 1)
The importance of lake identity for bacterial community composition (BCC) among communities receiving the same dispersal treatment declined with increasing dispersal rate (Fig. 2A)
Summary
Due to the concern of which consequences the loss of biodiversity will have on ecosystems, it is of considerable interest to evaluate the importance of biodiversity for ecosystem functions (e.g. [1,2]). The mechanisms by which communities assemble may be of importance for ecosystem functioning, since different diversity-productivity patterns can be obtained depending on whether communities are assembled through local (niche) or regional (dispersal) processes [3,4]. If assembly via dispersal is important for communities, dispersal should have an immediate effect on the composition. The functioning, on the other hand, should, in theory, increase with dispersal because of the inclusions of taxa with complementary traits. At high dispersal rates we may expect a decrease in functioning because of a dilution of locally adapted taxa [5]. If local niche processes are most important for the assembly of communities, dispersal should insignificantly affect community composition and function [5]
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