Abstract
The exotic South African ragwort (Senecio inaequidens DC.) rapidly spread across Central Europe after its introduction, but we still do not know to what extent its timing of arrival in a plant community (i.e. before or after natives) and the composition of the native community being invaded affect (1) its capacity to invade a European grassland, (2) the performance of the native species, and (3) the direction and strength of priority effects. In a greenhouse experiment, we manipulated the timing of arrival of the exotic species (Senecio) and the composition of the native community to test the influence of these factors on the productivity and N content of exotic and native species. We also investigated if the plant species origin (native or exotic) and the native community composition affected the benefit of arriving early and the cost of arriving late in the community. The establishment success of Senecio strongly depended on its timing of arrival in a grassland community. Senecio benefited more from arriving early than did the natives. The presence of legumes in the community did not favour invasion by Senecio. When natives arrived later than Senecio, however, priority effects were weaker when legumes were part of the native community. Our results showed that inhibitory priority effects created by natives can lower the risk of invasion by Senecio. An early arrival of this species at a site with low native species abundance is a scenario that could favour invasion.
Highlights
Invasion of plant communities by non-native (“exotic” or “alien”) species is largely recognized as one of the main drivers of biodiversity loss worldwide
If the native plant community contained both grasses and legumes, the biomass gain due to an early sowing of Senecio (+ 138%) was larger than when the native community contained only grasses (+ 64%). This result can be explained by the fact that, when both exotic and native species were sown at the same time, Senecio was less productive in communities containing legumes than in communities containing only grasses (Fig. 2a; z = 2.96, P = 0.01), while the biomass achieved by Senecio did not differ between both communities when it was sown earlier than the native species (Fig. 2a; z = − 0.15, P = 1.0)
When looking at the native species, the δ15N values measured in grass shoots were affected neither by the timing of arrival of the exotic species (Arrival: F3,32 = 1.59, P = 0.21) nor by the species composition of the native plant community (Composition: F1,32 = 1.17, P = 0.29; Interaction: F3,32 = 0.11, P = 0.95) (Fig. 6c)
Summary
Invasion of plant communities by non-native (“exotic” or “alien”) species is largely recognized as one of the main drivers of biodiversity loss worldwide Senecio is a large perennial forb whose seeds have been repeatedly introduced to locations in Central Europe via the transport of sheep wool imported from the Eastern highlands of South Africa (Ernst 1998; Lachmuth et al 2010) It was observed for the first time in Europe (West Germany) at the end of the nineteenth century (Ernst 1998; Heger and Böhmer 2005) and, after a time lag of nearly 80 years, it started to spread across Germany, mainly from a population introduced in Belgium at the beginning of the twentieth century (Lachmuth et al 2010). It is an early-successional ruderal species requiring open sites with little resource competition and is
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