title: Consumption rates and food preferences of slugs in a calcareous grassland under current and future CO2conditions.
abstract: This study explored consumption of a generalist herbivore feeding on leaf tissue of various plant species of a calcareous grassland, and tested whether consumption levels and preferences changed when plants were exposed to 5 years of in situ CO2enrichment. The first part of this experiment tested whether the consumption patterns of slugs (Deroceras reticulatum) observed in single-species feeding tests were altered when slugs were given a choice of food sources. Overall consumption increased 270% when slugs were given a choice, and they preferred having a choice of food sources more than they preferred having any one food source. Surprisingly, slugs consumed fewer legumes and grasses and more non-leguminous forbs when given a choice. In the second part of this experiment, feeding behaviors of slugs in response to elevated CO2were investigated by feeding them leaves of two legumes, one grass, and a non-leguminous forb (Trifolium medium, Lotus corniculatus, Bromus erectus, and Sanguisorba minor, respectively) in two or four species combinations. In the leguminous species mix, the non-leguminous species mix, and the combined mix (legumes and non-legumes), neither overall consumption by herbivores nor species preference was significantly altered by long-term CO2enrichment. In the combined species mix, slugs preferred legumes to non-legumes (P=0.012) and exhibited a weak functional group preference shift from non-legumes to legumes (P=0.089) in response to CO2enrichment. This is the first time such a shift has been observed, and provides evidence that there may be multiple herbivore responses to rising atmospheric CO2concentrations. Numerous single-species feeding tests using insects have shown that consumption by herbivores may increase when herbivores are fed plants grown in enriched CO2atmospheres. This study clearly demonstrates the limited applicability of non-choice feeding trials to generalist herbivores in species-rich communities.
authors.affiliation: Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK e-mail: halton_peters@post.harvard.edu Tel.: +44-1223-333900, Fax: +44-1223-333953, UK.
authors.forename: H A
authors.initials: HA
authors.lastname: Peters
authors.affiliation: Section of Conservation Biology (NLU), Department of Integrative Biology, University of Basel, St. Johanns-Vorstadt 10, 4056 Basel, Switzerland, Switzerland.
authors.forename: B
authors.initials: B
authors.lastname: Baur
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, The Biological Laboratories, 16 Divinity Avenue, Cambridge, MA 02138-2020, USA, USA.
authors.forename: F
authors.initials: F
authors.lastname: Bazzaz
authors.affiliation: Institute of Botany, University of Basel, Schoenbeinstr. 6, 4056 Basel, Switzerland, Switzerland.
authors.forename: Ch
authors.initials: C
authors.lastname: Körner
keywords: Alternative feeding; Global change; Herbivory; Key words Elevated CO2; Legumes