Differences in herbivore damage to Arctium minus in open and forest habitats in its non-native range.

Exotic plants do not always escape enemies in new areas; instead, they may be damaged by co-invading non-native enemies or by enemies recruited from native species. However, even when such enemies exist in an invader's new range, escape may still be possible if particular habitats offer low-damage refuges. In this study, herbivory on the non-native common burdock ( Arctium minus (Hill) Bernh.) were compared between open and understory habitats, with high and low sunlight exposure respectively, on five sites in Ontario, Canada. Open-habitat populations showed relatively reduced herbivore damage; this may be due to herbivores occurring less abundantly in open habitats or burdock expressing greater defences in open sites. These results emphasize that enemy release is not an absolute effect, but can depend on an individual's habitat. As well, they suggest herbivory potentially may help to confine burdock primarily to open habitats. [ABSTRACT FROM AUTHOR]