Compensatory dynamics among populations influence community variability more strongly than diversity in plankton populations.
Gaedke, Ursula*,1, 1 Institute for Biochemistry and Biology, Potsdam, Germany
ABSTRACT- Short- and long-term variability at the population and community level were compared among three species-rich plankton groups (phytoplankton, ciliates, rotifers) using long-term high frequency observations from Lake Constance. Each group was subject to the same environmental forcing and the objective was to disentangle the various processes influencing temporal variability in natural populations. Phytoplankton and ciliates exhibited a similar variability at the community level although their population dynamics were markedly different. Community variability is influenced by (1) the relative variability of the individual populations, (2) the diversity-dependent Portfolio effect, and (3) the diversity-dependent dampening by negative covariances among populations. The relative variability of individual populations was smallest in ciliates, intermediate in phytoplankton and largest in rotifers. Diversity was highest in ciliates, intermediate in phytoplankton and lowest in rotifers. High diversity promotes the Portfolio effect and may promote diminished community variability if populations fluctuate asynchronously yielding some negative covariance among them. Differences in the synchronicity of population variations among ciliates, phytoplankton, and rotifers led to notable differences in community variance. The diverse ciliate community was characterized by small but relatively synchronized population fluctuations, while the less diverse phytoplankton community exhibited larger but asynchronous fluctuations resulting in similar community-level variability. In rotifers, the high population variability and low diversity was not fully compensated by more asynchronous fluctuations which resulted in a higher community variability than found in ciliates and phytoplankton. This field study shows that diversity and community variability are not neccessarily linked. Diversity is a neccessary but not sufficient prerequisite for a large reduction in variability from the population to the community level which demands in addition that individual populations fluctuate asynchronously. This may or may not be linked to high diversity.
Key words: diversity, stability, variability, plankton
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