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Trophic Implications of Plant Invasions (TIPI)

Jonathan Rosenthal

The trophic interaction between herbivorous insects and invasive plants has been a major focus of invasive plant research, largely for the purpose of determining whether invasions have been facilitated by escape from herbivory. However, consequences for higher level consumers from changes in herbivorous insect fauna due to plant invasion have not been investigated in any published studies. If invasive plants were to escape completely from herbivory, invasions would have disastrous impacts on such secondary consumers, and should be of great conservation concern. Indeed, such a phenomenon could underlie, at least in part, the dramatic declines in many neotropical migratory songbird populations, as many of these species rely largely upon the herbivorous larvae known as caterpillars to feed their young.

However, although virtually complete escape from insect herbivory has occurred for several taxa of invasive plants in particular geographic areas, exotic plants in general are typically colonized by some herbivorous insects – generalists, as well as specialists that switch hosts from closely related native species. Therefore, effects of plant invasions on higher level consumers are likely to be more subtle. This project aims at detecting these effects on insectivorous, foliage-gleaning birds. One of the ways which we are approaching this question is by comparing the herbivorous insect fauna found on 5 native shrub species and 2 invasive species both inside mesh cages (exclosures) and outside these cages. The comparison of the exclosure effect on the insect communities on the native and invasive plants should indicate the relative degree to which birds consume these insects on the different plants.