Figure 1. Hypothetical food interaction webs with co-occurring native and invasive species adapted from Zavaleta, Hobbs & Mooney (2001).

The trophic level of co-occurring invaders could influence outcomes when a single invasive species is removed (red cross; B–D). In (A) hypothetical food web based in interaction of carnivore top predators, omnivores, herbivore preys and plants. In (B) the removal of a carnivore releases nonnative herbivores, and native omnivores and predators. In (C) the removal of a nonnative herbivore reduces population size of the competing native herbivore. In (D) the removal of only one invasive carnivore releases the other invasive carnivore predating on native herbivores and native omnivores reducing their populations. Thicker lines represent larger population sizes.