Effects of phytoplankton diversity on intraspecific competition in Daphnia - A common garden experiment
Effects of phytoplankton diversity on intraspecific competition in Daphnia - A common garden experiment
Abstract
Biodiversity loss in aquatic ecosystems is believed to have cascading effects on multiple trophic levels. In particular the phytoplankton-zooplankton interface is of high interest, as the phytoplankton content of dietary polyunsaturated fatty acids (PUFAs) was found to be crucial for the fitness of the herbivorous grazer Daphnia, which is not capable of de novo synthesis of such PUFAs. Essential PUFAs are thus assumed to be a functional phytoplankton trait that affects the trophic transfer efficiency and dynamics between the primary producers and consumers. However, fatty acid composition of the phytoplankton was shown to be taxon-specific. Thus, we hypothesized that altered phytoplankton community composition will result in an altered composition of dietary fatty acids. This in turn will affect the intraspecific competition in Daphnia. To address these hypotheses, we performed a common garden experiment with diversity-manipulated natural phytoplankton community and naturally coexisting D. longispina genotypes with pronounced differences in their susceptibility to limitations by essential dietary fatty acids. Our data demonstrate that the phytoplankton diversity is correlated with the fatty acid composition, but that this does not directly affect competitive interactions between the tested D. longispina genotypes. This indicates that upscaling results from single clone microcosm experiments to complex natural communities should be treated with care and that competitive interactions under more natural conditions are more complex.
