PARENT SESSION
Poster Session 20: Invasive Species
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Native insect herbivory provides resistance to a thistle invasion.
Young, Lauren*,1, Louda, Svata2, 1 Indiana University, Bloomington, IN2 University of Nebraska, Lincoln, NE
ABSTRACT- The factors limiting plant invasiveness are still largely unknown. Biotic resistance to invasion by natural enemies is an important, still under-evaluated hypothesis. If a naturalized plant encounters effective herbivores in the new range, then populations of the species could fail to grow and spread in the new range. We tested this hypothesis by manipulating exposure of a naturalized thistle (Cirsium vulgare) and its synchronously flowering native congener (C. altissimum) to native insect herbivores in eastern Nebraska. When floral herbivory by native insects was experimentally reduced, viable seed production increased four-fold for naturalized C. vulgare, compared to three-fold for its native congener, C. altissimum. In addition, the stem-boring insect guild also imposed significant damage. We also compared our data on insect herbivore impact on C. vulgare in tallgrass prairie with data published in three other studies investigating herbivory on C. vulgare, both within its native range (United Kingdom) and two other natualized ranges (New Zealand, coastal California). Surprisingly, native insect herbivore impact on C. vulgare was greater in eastern Nebraska (naturalized range) than in the United Kingdom (native range) as well as in New Zealand and California (other naturalized ranges). Our study experimentally demonstrates that native herbivores significantly depress reproductive performance of naturalized C. vulgare in its new prairie environment, and do so to a greater extent than reported in the native range. Thus, this study provides direct evidence of significant resistance to invasive population growth and potential spread by a non-native plant in a region where synchronously flowering native relatives support an array of pre-adapted natural enemies.
Key words: insect herbivory, invasive species, thistles, invasion biology