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posted by cornelia on 22.09.2010.

Dispersal-Dormancy Relationships in Annual Plants: Putting Model Predictions to the Test. By Wolfgang Siewert and Katja Tielbörger

Plants are immobile, aren’t they? Plants don’t use dispersal to spread extinction risk. This is the surprising result of a large-scale field experiment that Wolfgang Siewert and Katja Tielbörger from Tübingen University, Germany, conducted in Israel in 2007 and 2008. Using a novel experimental approach, they were able to evaluate the consequences of seed dispersal for the population dynamics of more than 100 plant species. Sessile and short-lived organism like annual plants are thought to be vulnerable to unpredictable risks like unexpected drought years or locally unfavorable conditions, because they could not run away once they germinated. Theoretical models say that seed dispersal and seed dormancy are two alternative strategies for annuals to reduce extinction risk, because they allow annuals to escape the risk in space or in time.
However, the experiments conducted in highly unpredictable environments indicated extremely low dispersal in all species, no matter how dormant their seeds. These findings contradict the well accepted theory of a trade-off between dispersal and seed dormancy that was proposed more than 20 years ago. “It is amazing that in all these years nobody ever went to the field to properly put the theory to the test,” says Wolfgang Siewert. “It shows how important it is to do multi-species and multi-site experiments in ecology.” (Copied from:

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