Ecological theory postulates a trade-off between competition and colonization ability. This hypothesis was tested with artificial benthic communities in two microcosm experiments. Tiles covered by a biofilm of a benthic diatom, bacteria and heterotrophic flagellates were used as artificial substrates. Six benthic ciliate species served as test organisms. For each species, colonization ability was measured by connecting two microcosms and detecting the time necessary to reach the initially uncolonized microcosm. Competitive ability was measured by adding species pair-wise to unconnected microcosms. Abundances of the ciliates and concentrations of the three resource types were measured in weekly intervals, and the species with the higher biomass at the end of the experiment was regarded as the better competitor.

Results/Conclusions

Species strongly differed in their colonization ability. Colonization time ranged from 1.7 to 8.7 days. A clear winner and a clear loser were found in the competition experiment, but also some species with similar competitive abilities. The relationship between competitive and colonization ability was positive rather than negative, contrary to the competition-colonization trade-off hypothesis.