Alien plants are rapidly replacing native species throughout North America. Large-scale replacement of native vegetation has several consequences, but one that has received little attention is the effect of alien plants on insect herbivores. Insects capable of eating only a few types of plants should be unable to grow and reproduce on plants with which they share no evolutionary history. Because most insect herbivores are such specialists, alien plant invasions should reduce local biodiversity, which in turn may reduce ecosystem stability and productivity. Specialists may, however, be able to adopt alien species that are closely related to their native plant host with few negative effects. Insects that are able to use many plant species, in contrast, should be unaffected by aliens and may compensate for the loss of specialists. Existing data are few but they support neither of these predictions. In view of the critical role of herbivorous insects in transferring energy from plants to other animals, it is essential to understand how alien plants affect the production and diversity of insect herbivores. This project addresses this need by quantifying 1) the degree to which specialists switch to aliens related to their native hosts; 2) the success of generalists on alien and native plants; and 3) how the behavior of specialists and generalists toward aliens is affected by the proportion of alien biomass in the habitat.
A graduate student and several undergraduates will be trained in field population sampling and insect taxonomy and will gain valuable exposure to the growing field of biological invasions. This study will also help to fill long-standing gaps in our knowledge of plant-insect interactions, such as whether generalists drive food webs more than specialists. The results of this study will be disseminated in the primary literature and also in popular-science publications to target the environmentally-minded public.
