Fine‐tuned ability to predict future competitive environment in A mbrosia artemisiifolia seeds

Summary Competition from native species is a key mechanism for biotic resistance to invasion. Accelerated germination to pre‐empt resources or delayed germination and induced dormancy until the next growing season are two alternative strategies for annual invasive plants to avoid the drawbacks of competition at the seed stage. In A mbrosia artemisiifolia , both of these tactics could theoretically increase its long‐term fitness. However, their relative importance has never been tested. We studied the germination pattern of A . artemisiifolia seeds in various competitive environments by experimentally modifying the life stage (seed, seedling, adult), density (low, high) and also the identity (intraspecific and 3 interspecific competitors) of neighbours in controlled conditions. When facing competition of seeds and seedlings at high densities or of particular identity, A . artemisiifolia accelerated its germination. In contrast, A . artemisiifolia followed a competition avoidance strategy in the presence of established adult heterospecific neighbours by delaying germination and reducing the germination fraction through induction of secondary dormancy. By testing the seedlings' performance in the same competition situations as those of seeds, we showed that the germination responses were beneficial in the case of heterospecific, but not of conspecific neighbours.