EEB Seminar- September 28th

This week the department is pleased to welcome Peter Kotanen from University of Toronto Mississauga.

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Latitudinal and local variation in damage by above- and below- ground enemies of an invasive thistle

Non-native plants frequently escape their native-range natural enemies (herbivores and pathogens) while colonizing new geographic regions. However, once in a new region, these invaders often acquire new enemies recruited from native plants; as well, enemies from the invader’s original range may be accidentally or deliberately co-introduced. Even so, escape might continue to benefit such invaders as they repeatedly colonize new sites. In this talk, I’ll discuss some of our recent work on a Eurasian thistle, Cirsium arvense, which has widely invaded here in Ontario. We documented herbivore damage to C. arvense by sampling plants over a 800 km transect from agricultural southern to boreal northern Ontario. We also monitored colonization of artificial populations, and investigated soil feedback using inocula sampled at both local (inside/outside existing populations) and geographic scales. Results indicate that thistle populations host a diverse set of herbivores, but their impacts generally decline with latitude. Plants inoculated with northern soils outperformed those inoculated with southern soils, suggesting the reduction of pathogens at northern sites. At a local scale, artificial populations were colonized rapidly by herbivores, but even short (<100m) separation from other populations significantly slowed this process. Similarly, plants grown in soils inoculated with samples from outside thistle populations performed better than plants inoculated with soil from invaded areas only 50-100 metres away. These results indicate that C. arvense can temporarily escape many of its natural enemies by founding new populations. Plants near this thistle’s northern range margins may experience more lasting reductions in damage. Escape from enemies therefore may contribute to the success of this thistle both in local spread to new sites, and in expanding its future range.

The EEB Seminars run weekly, on Thursdays, in the EEB Lounge of the BioSciences Complex, Room 4338, from 12:30-1:30pm. This week there will be a pizza lunch to follow in the EEB Lounge.

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