Scale-dependent changes in species richness caused by invader competition

Ecologists have produced substantial literature about the impact of biological invasions on species diversity. However, due to scale-dependent factors, no consistent conclusion has been reached regarding whether biological invasion leads to a loss of species diversity. In this project, we incorporate an invasion scenario into community assembly theories through spatially explicit individual-based models. We explore how invader dominance shifts community richness at local scales and how local-scale extinctions translate to broader scales. To do so, native community dynamics are simulated according to the niche-neutral continuum theory and constructed on a heterogeneous landscape with a limited environmental gradient. We synthetically assume that the establishment of invaders is wholly affected by their niche or fitness difference from native populations. By analyzing richness changes across all sample sizes, we obtained the following results: (1) for randomly distributed habitat resources, the magnitude of richness loss linearly decreases with sample size when strong niche overlap occurs, but the magnitude is more nonlinearly shaped in communities assembled by niche departures; (2) spatially structured native populations could have greater resistance to invasion competition, and if on clustered habitats and the species suffering more niche overlap, then larger extinction events would occur at broader scales; and (3) these invasion modification trends could be linked with native population spatial structures and abundance evenness. The above findings are solely based on simulation experiments and implemented under several synthetic assumptions. This suggests theoretical linkages between invasion scale-dependent influences and mechanistic issues, such as the properties of the invader and invaded communities, which can inform invasive species management and restoration.