Non-native plant invader renders suitable habitat unsuitable

Coevolution between insect herbivores and their target plants often prompts an evolutionary arms race so that insects develop methods to overcome plant defenses. In doing so, some insects become specialized on host plants so that suitable habitat for these herbivorous insects may be demarcated by coevolved plant species. Non-native plant species may render suitable habitat unsuitable by replacing palatable native species with novel defenses that deter native herbivores. We investigated these dynamics in an urban forest heavily invaded by a non-native shrub (Rhamnus cathartica). We experimentally introduced native trees into a non-native dominated urban forest and found significantly higher Lepidoptera larvae abundance and diversity, and overall herbivory, on the native than non-native species. Hence, we rendered unsuitable habitat suitable by providing a key biotic niche requirement: palatable plants. These results suggest that non-native plants may simplify ecological systems by eliminating critical niche requirements for native species.