Direct and indirect effects of native plants and herbivores on biotic resistance to alien aquatic plant invasions

1- Biotic resistance to alien plant invasions is mainly determined by ecological interactions in two layers of the food web: competition with native plant species, and herbivory by native herbivores. While the direct effect of native plants on alien plant performance via competition has been well documented across ecosystems, less is known about the direct and indirect effects of herbivores in providing biotic resistance. Our main aims were to determine whether temperate native aquatic plants and herbivores can provide biotic resistance to plant invasions, understand the underlying mechanisms and search for potential interactive effects of competition and herbivory on invader performance (i.e. growth). 2- We mimicked natural temperate mesotrophic and eutrophic freshwater lakes in mesoscosms, by growing three native submerged plant species in monocultures (Ceratophyllum demersum, Myriophyllum spicatum and Potamogeton perfoliatus) at three competition levels (no, low and high) without ...