The exotic species Senecio inaequidens pays the price for arriving late in temperate European grassland communities

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.