Land use, biological invasions and local species diversity

Human agency threatens global biodiversity. Among human activities, land use has so far had the most detrimental impact on plants and animals. However, land use effects often combine with additional human pressures such as the intentional or unintentional translocation of species beyond their native ranges. These pressures may combine and interact, for example because certain types of land use foster the establishment of alien species. As a consequence, negative effects of land use on biodiversity might even be more severe than assumed because exchange of native by alien species masks the full extent of native species loss. Although the impact of land use on the distribution of alien species has been documented in several studies, a global scale analysis of how land use affects the ratio of aliens to natives in species communities is lacking so far. Moreover, little effort has so far been made to predict how land use and species introductions may affect future biodiversity in the decades to come. In the proposed project, we will combine the largest and geographically and taxonomically most comprehensive databases on the global distribution of alien species with a similarly large database documenting how land use has changed the species compostion of c. 29,000 local assemblages in 94 countries. We will analyse the combined data with respect to the following questions: (1) How do type and intensity of land use affect the ratio of alien to native species in local communities across global terrestrial ecosystems? Do these effects differ among taxonomic groups or biomes? (2) Does the effect of land use on the ratio of alien to native species depend on the regional history of biological invasions and are there signs of an invasion debt? (3) What are the interactive effects of land use and alien species on the taxonomic homogenization of species communities? Finally, we will use the relationships found in an attempt to forecast how (4) the ratio of alien to native species in local st assemblages may change until the end of the 21 century under different scenarios of global land use development. Our study will provide the first global, multi-taxon analysis of how land use alters the relative contribution of native and alien species to the diversity and composition of local assemblages across terrestrial biomes. It will moreover add a novel aspect to predictive biodiversity modelling in that it tries to forecast how relative contributions of native and alien species to local communities may change until the end of the century.