Schulze, Leona Julia (2013) Experimental tests of dispersal frequency on phytoplankton diversity in source-sink metacommunities. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 35 pp.

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Abstract

Dispersal has not only effects at local scales but also on regional and global scales and it is well known that dispersal is a community structuring factor. The metacommunity concept provides an excellent framework for testing the importance of dispersal for local and regional diversity and ecosystem functioning. In this experiment metacommunities with three phytoplankton species (C. curvisetus, E. huxleyi and N. spumigena) in different nutrient regimes (P-limited, N-limited and Redfield-ratio with excess silica), were connected via several dispersal levels (0,1,2,7,14). Preference of a different nutrient regime by each species resulted in species sorting and source-sink dynamics within these metacommunities. α, β and γ-diversity were measured as well as local and regional ecosystem functioning, here biomass (calculated as biovolume). Even with C. curvisetus dominant in all nutrient regimes, local (α-) diversity was significantly affected by dispersal and showed the highest biodiversity with intermediate dispersal level, caused by source-sink dynamics among local patches with different nutrient regimes. Homogenization of the communities among nutrient regimes with increasing dispersal rates resulted in a significant linear decrease of in-between-community (β-) diversity (calculated as Bray-Curtis dissimilarity). Likewise to α-diversity, regional (γ-) diversity showed a hump shaped significant change. Source-sink dynamics caused the highest regional biodiversity at intermediate dispersal rates. Regional communities become homogenized at high dispersal rates, which reduced coexistence on local scale and therefore the best regional competitor outcompeted the other species, thus leading to a reduction of regional biodiversity. Local and regional biomasses were not affected by dispersal rates, except within the Redfield-ratio with excess silica nutrient regime, where biomass increased linearly with increasing dispersal rate. Correlating local biodiversity and biomass of this nutrient regime resulted in a marginal significant (p < 0.06) linear decrease of biomass with increasing biodiversity, showing that communities inhabited by dominant species have higher ecosystem functioning then a more diverse community.

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