Potential problems of removing one invasive species at a time: a meta-analysis of the interactions between invasive vertebrates and unexpected effects of removal programs

Although the co-occurrence of nonnative vertebratesis a ubiquitous global phenomenon, the study of interactions between invaders is poorly represented in the literature. Limited understanding of the interactions between co-occurring vertebratescan be problematic for predicting how the removal of only one invasive—a common management scenario—will affect native communities. We suggest a trophic food webframework for predicting the effects of single-species management on native biodiversity. We used a literature search and meta-analysis to assess current understanding of how the removal of one invasive vertebrateaffects native biodiversity relative to when two invasives are present. The majority of studies focused on the removal of carnivores, mainly within aquatic systems, which highlights a critical knowledge gap in our understanding of co-occurring invasive vertebrates. We found that removal of one invasive vertebratecaused a significant negative effect on native species compared to when two invasive vertebrateswere present. These unexpected results could arise because of the positioning and hierarchy of the co-occurring invasives in the food web(e.g., carnivore–carnivoreor carnivore–herbivore). We consider that there are important knowledge gaps to determinate the effects of multiple co-existing invaders on native ecosystems, and this information could be precious for management.