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Journal Article

Thorns as Induced Mechanical Defense in a Long-Lived Shrub (Hormathophylla spinosa, Cruciferae)

José M. Gómez and Regino Zamora
Ecology
Vol. 83, No. 4 (Apr., 2002), pp. 885-890
Published by: Wiley on behalf of the Ecological Society of America
DOI: 10.2307/3071897
Stable URL: http://www.jstor.org/stable/3071897
Page Count: 6
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Thorns as Induced Mechanical Defense in a Long-Lived Shrub (Hormathophylla spinosa, Cruciferae)
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Abstract

We have experimentally tested under natural conditions the cost and inducibility of thorns in Hormathophylla spinosa (Cruciferae), a shrub heavily damaged by ungulates. We first excluded ungulates from 40 shrubs, 20 in each of two years (1992 and 1998), to test for a negative phenotypic correlation between thorn density and seed production. Next, we removed thorns from 20 protected shrubs to compare seed production in thornless shrubs vs. control plants (also excluded from ungulates). Finally, we monitored the change in thorn production for three years in the 1998 ungulate-exclusion experiment to test whether plants growing in an herbivore-free environment would reduce thorn production. Thorns seem to be phenotypically costly for H. spinosa, since a negative correlation with percent fruit set was found in both years, and thorn removal in the second experiment enhanced seed production. In addition, thorn density significantly decreased from the first to the second and the third years in shrubs excluded from ungulates in the 1998 experiments. These results suggest that thorns are induced defense in H. spinosa.

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