Herbivore pressure on native and non-native plant species
In the field survey of 28 sites, 396 individuals of 27 non-native plant species and 678 individuals of 59 native plant species were evaluated. There were large differences among non-native plant species (χ² = 3744, P < 0.001, Figure 1A) and among native species (χ² = 3025, P < 0.001, Figure 1B) in herbivore damage, with non-native plant species damaged 46.2% less than natives (χ² = 22.63, P<0.001, Figure 1C).
In the common garden experiment, herbivore damage varied by over an order of magnitude among non-native species (χ² = 198.43, P < 0.001, Figure 1D) and among native species (χ² = 71.22, P < 0.001, Figure 1E). Herbivore damage on non-native species was 41.5% less than on natives (χ² = 6.53, P = 0.011, Figure 1F).
Non-native plant species with higher herbivore biomass on them received more leaf damage in the field survey (r = 0.97, P < 0.001, Figure S3A) and in the common garden (r = 0.38, P < 0.001, Figure S3B). Furthermore, there was a strong positive linear relationship between herbivore damage on particular species in the field survey and those species in the common garden experiment (r = 0.88, P < 0.001, Figure S4).