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Demographic and evolutionary impacts of native and invasive insect herbivores on Cirsium canescens

Rose, K.E., Louda, S.M. and Rees, M. (2005) Demographic and evolutionary impacts of native and invasive insect herbivores on Cirsium canescens. Ecology, 86 (2). pp. 453-465. ISSN 0012-9658


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Invasive species have the potential to alter trade-offs leading to selection in the populations they invade. Here we quantify the demographic and selective effects of herbivory by native insects and the introduced floral feeder Rhinocyllus conicus on Platte thistle (Cirsium canescens), a sparse monocarpic thistle endemic to North America. Rhinocyllus first invaded the Platte thistle population in 1993. Since then, its numbers have increased exponentially, while the Platte thistle population size has decreased. Data from 11 years were analyzed to determine how demographic rates varied with plant size and damage by native insects and Rhinocyllus. Individual growth, survival, flowering probability, and seed set were all size dependent. Damage to vegetative structures did not influence demographic rates; damage to flower heads did because Platte thistle is seed limited. These analyses were used to parameterize a series of integral projection models (IPMs) that investigated the effects of floral herbivory on the population growth rate λ, equilibrium population size, and the evolutionary stable (ES) flowering strategy. The IPMs showed that native insects have significant impact on the equilibrium population size and λ, but not the ES flowering strategy, because they use the flowers of different-sized plants indiscriminately. In contrast, Rhinocyllus has the potential to drive Platte thistle extinct. Rhinocyllus preferentially fed and oviposited on the flowers of larger plants and therefore selected for a reduction in flowering size. However, as the thistle population went into decline, this pattern reversed. Thus, selection imposed by an invader may be complex and will reflect behavioral interactions between herbivore and host, as well as demographic changes in the host population.

Item Type: Article
Copyright, Publisher and Additional Information: © Copyright 2005 by Ecological Society of America. Reproduced in accordance with the publisher's self-archiving policy.
Keywords: biological control, Cirsium canescens, evolutionary stable strategy, insect herbivore, integral projection model, invasive species, life history evolution, monocarpic perennial, Platte thistle, Rhinocyllus conicus, selection
Institution: The University of Sheffield
Academic Units: The University of Sheffield > Faculty of Science (Sheffield) > School of Biological Sciences (Sheffield) > Department of Animal and Plant Sciences (Sheffield)
Depositing User: Repository Officer
Date Deposited: 27 Jul 2006
Last Modified: 10 Jun 2014 21:09
Status: Published
Publisher: Ecological Society of America
Refereed: Yes
URI: http://eprints.whiterose.ac.uk/id/eprint/1466

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