Complex interactions between spatial pattern of resident species and invasiveness of newly arriving species affect invasibility

Abstract

Understanding the factors that aVect establishment success of new species in established communities requires the study of both the ability of new species to establish and community resistance. Spatial pattern of species within a community can aVect plant performance by changing the outcome of inter-speciWc competition, and consequently community invasibility. We studied the eVects of spatial pattern of resident plant communities on Wtness of genotypes from the native and introduced ranges of two worldwide invasive species, Centaurea stoebe and Senecio inaequidens, during their establishment stage. We experimentally established artiWcial plant mixtures with 4 or 8 resident species in intra-speciWcally aggregated or random spatial patterns, and added seedlings of genotypes from the native and introduced ranges of the two target species. Early growth of both S. inaequidens and C. stoebe was higher in aggregated than randomly assembled mixtures. However, a species-speciWc interaction between invasiveness and invasibility highlighted more complex patterns. Genotypes from native and introduced ranges of S. inaequidens showed the same responses to spatial pattern. By contrast, genotypes from the introduced range of C. stoebe did not respond to spatial pattern whereas native ones did. Based on phenotypic plasticity, we argue that the two target species adopted diVerent strategies to deal with the spatial pattern of the resident plant community. We show that eVects of spatial pattern of the resident community on the Wtness of establishing species may depend on the diversity of the recipient community. Our results highlight the need to consider the interaction between invasiveness and invasibility in order to increase our understanding of invasion success.