Lecture: Limits to the invasiveness of Erigeron annuus in Switzerland
Botanical seminar, KU-LIFE, October 10, 2008, at 14:15-15:00. Lecture by Sabine Güsewell, Institute of Integrative Biology, Department of Environmental Sciences, ETH Zürich.
Main building, meeting room, KU-LIFE Rolighedsvej 21, Frederiksberg
We investigated the ecological limits of the winter annual forb Erigeron annuus in Switzerland to understand why the species is currently becoming more invasive. Until recently, E. annuus was restricted to the lowlands and to open, disturbed habitats, but it now seems to be spreading upward and into more closed vegetation.
To understand what limits the altitudinal range of E. annuus, we surveyed populations along roads between 240 and 1100 m a.s.l., and grew plants in common gardens at 400 and 1000 m. Winter survival was reduced at the current altitudinal limit. High-altitude populations were genetically less diverse than low-altitude populations and did not show evidence of local adaptation.
To understand what restricts the colonization of closed habitats, we compared E. annuus to S. gigantea, a species able to invade open and closed habitats. E. annuus was not less plastic in shade-avoidance or shade-tolerance traits than S. gigantea, nor did allelopathic effects differ consistently. However, E. annuus was highly palatable to slugs and strongly affected by herbivory in the field.
Recent changes contributing to the increasing invasiveness of E. annuus might be (1) greater chance of winter survival at higher altitude due to climate warming, (2) summer drought, allowing the establishment and spread of E. annuus in grasslands, and (3) more plants escaping from slug damage once large populations have become established.
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