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Shoot Survival under Intense Grazing for Two Broad-Leaved Herbs with Different Chemical Defense Systems

Jon Moen, Hans Gardfjell, Lars Ericson and Lauri Oksanen
Oikos
Vol. 75, No. 3 (Apr., 1996), pp. 359-364
Published by: Wiley on behalf of Nordic Society Oikos
DOI: 10.2307/3545875
Stable URL: http://www.jstor.org/stable/3545875
Page Count: 6
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Shoot Survival under Intense Grazing for Two Broad-Leaved Herbs with Different Chemical Defense Systems
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Abstract

Shoot survival of a toxic herb, Actaea spicata, and a herb with a digestibility-reducing defense, Geranium sylvaticum, was studied in an experimental set-up where microtine rodents were allowed to graze freely. It was hypothesized that the defense system of Actaea would work in a risk-reducing way, while the defense system of Geranium would have cost-reducing properties. If so, shoot survival of Actaea would be higher at all times than for Geranium, and shoot survival would also be higher for Actaea when grazed by a more generalized herbivore (Microtus agrestis) than by a more specialized one (Clethrionomys rufocanus). Using failure-time analyses, it was shown that Actaea indeed had a significantly higher shoot survival than Geranium in all treatments but one, and that survival was also higher when grazed by the generalist than by the specialist. It was concluded that the defense system of Actaea had stronger characteristics of a risk-reducing defense than that of Geranium.

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