Invasive Melinis minutiflora outperforms native species, but the magnitude of the effect is context-dependent

Impacts of invasive species are context-dependent owing to genetic differences in the invasive species, in the abiotic environment or the recipient biotas. Here, we tested how these factors affected the invasive grass Melinis minutiflora and its impacts on native plants in Hawai’i (USA) and in the Brazilian Cerrado under four environmental conditions. We sampled M. minutiflora and three native species from each studied region and conducted two equivalent greenhouse experiments. In each experiment, we manipulated shade, irrigation, soil nutrients, and interspecific competition. We found that M. minutiflora had low genetic polymorphism, and two distinct genetic clusters exist. Both clusters exist in Hawai’i and Brazil. Melinis minutiflora biomass was three-times greater in Brazil compared to Hawai’i. Both in Brazil and Hawai’i, M. minutiflora was affected by shade, irrigation, and competition. While in Brazil the identity of the competing native species did not matter for M. minutiflora , in Hawai’i the identity of the native species affected M. minutiflora when shade was applied. Brazilian native species were all affected by shading, two of them by competition with M. minutiflora , and one of them by fertilization. Two Hawaiian native plants were affected by shade and competition with M. minutiflora , whereas one native species was not affected by any of the experimental factors. In summary, both biotic and abiotic factors affected native and invasive species. However, in all cases native species were outperformed by the invader.