Document: JEA-3-42-1

Eat green but not any green! Consequences of ungulate introduction on an long-lived tree species.

VOURC'H, G.* ¹, B.VILA ², D.GILLON ¹, T.P.CLAUSEN ³, J.ESCARRÉ ¹ and J.MARTIN ¹

Centre d'Ecologie, Fonctionelle et Evolutive, CNRS, Montpellier, France ¹
Institut Méditerranéen d’Ecologie et de Paléoécologie, CNRS, Marseille, France ²
University of Alaska Fairbanks, Fairbanks, AK, U.S.A. ³

Abstract:
Forests on the Haida Gwaii archipelago (British Columbia, Canada) evolved for c. 10 000 years in the absence of large mammal browsing. The introduction of black-tailed deer (Odocoileus hemionus sitkensis) from the mainland c. 1910 provides an opportunity to evaluate changes in the adaptive defensive responses of plants to herbivory. Our preliminary study showed that Haida Gwaii redcedars (Thuja plicata) that have never been browsed by deer (old trees that grew before deer were introduced and nursery-grown seedlings) had less effective defences than mainland plants, whereas Haida Gwaii and mainland saplings had a similar vulnerability to deer. In this study we assessed whether there was variability in defences among Haida Gwaii saplings and if deer acted as a selective force by choosing saplings with lower defences. We compared heavily and lightly browsed saplings on Haida Gwaii in terms of (i) chemical defence (terpene concentrations) and (ii) age and growth patterns (dendroecology). In addition, we tested the effect of monoterpenes found in redcedar leaves by food choice experiments on deer and showed that the major monoterpene (thujone) was repulsive to deer. Heavily browsed saplings had lower monoterpene profiles but were the same age as lightly browsed saplings. This suggests that under the current browsing regime, individuals with the greatest constitutive defences, or with greatest potential for induced defences grow better and are therefore selected on Haida Gwaii.

Keywords: herbivory, plant defences, terpene, introduction, island, deer

This abstract is being presented at: 3:15 PM in session:
Oral Session #17: Mammalian Herbivory.