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Gray-sided voles increase the susceptibility of northern willow, Salix glauca, to invertebrate herbivory
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2007 (English)In: Ecoscience, ISSN 1195-6860, Vol. 14, no 1, 48-54 p.Article in journal (Refereed) Published
Abstract [en]

The relationships between grey-sided vole (Clethrionomys rufocanus) densities, levels of invertebrate herbivory on Northern willow (Salix glauca) leaves, and chemical quality of the willows was studied on 8 islands and 2 mainland sites with contrasting vole densities in northernmost Norway. These variables were measured at each of the study sites to determine the degree and nature of the effects of browsing-induced alterations in plant quality on subsequent invertebrate herbivory. The level of invertebrate herbivory was positively correlated with vole density, as were the number of leaves per shoot, leaf size, and leaf nitrogen content, while leaf C/N ratios were negatively correlated with vole density. The level of herbivory increased from > 1% on the vole-free island to < 4% on the island with the highest vole density. The plant character that explained most of the variance in the level of invertebrate herbivory was leaf size. Since the vole densities have been altered by human intervention and their numbers are largely governed by predation rather than food quality, the positive correlation between vole densities and level of invertebrate herbivory is probably due to a facilitative effect of voles on invertebrate herbivores, mediated through changes in plant chemistry. We suggest that voles affect susceptibility of willows to invertebrate herbivory both directly by winter browsing and indirectly by reducing the abundance of competing plants.

Place, publisher, year, edition, pages
2007. Vol. 14, no 1, 48-54 p.
Keyword [en]
grey-sided voles, herbivory, phenols, plant resistance, susceptibility, willow, campagnols de Sundevall, herbivorie, phénols, résistance de la plante, saule, susceptibilité
Identifiers
URN: urn:nbn:se:umu:diva-5159DOI: 10.2980/1195-6860(2007)14[48:GVITSO]2.0.CO;2ISI: 000245364700007OAI: oai:DiVA.org:umu-5159DiVA: diva2:144562
Available from: 2006-05-10 Created: 2006-05-10 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Interactions between gray-sided voles (Clethrionomys rufocanus) and vegetation in the Fennoscandian tundra
Open this publication in new window or tab >>Interactions between gray-sided voles (Clethrionomys rufocanus) and vegetation in the Fennoscandian tundra
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

I have, in this thesis, studied the interactions between gray-sided voles (Clethrionomys rufocanus) and tundra vegetation, on islands in, and mainland sites close to the lake Iešjávri, in northern Norway. As isolated islands are virtually free of predation, I have been able to compare plant-herbivore interactions in the presence and absence of predators. I transplanted vegetation from an island with predators and voles, to predator-free islands with and with out voles. The results reveal the existence of a terrestrial trophic cascade as voles had a severe impact on the transplanted vegetation on the predator-free islands, but only minor effects on the mainland where predators are present. Moreover, this study shows that plant defence was only a successful strategy when predators were present. Voles reduced the abundance of all available plants during winter on the predator-free islands. The results imply that cascading effects of predation are most important for well-defended plants with grazing-sensitive morphology as these plants escape herbivore impacts in the presence of predators but are vulnerable in their absence

I studied the recovery of intensively grazed vegetation by building exclosures on islands that have been heavily grazed by voles for almost a decade.This study shows that the collective biomass of vascular plants recovered completely on three years, when voles were excluded. Although most species that are dominating the ungrazed vegetation recovered rapidly in the exclosures, the vegetation did not simply return to its ungrazed state. Herbaceous plants increased and there were pronounced differences in response among evergreen dwarf-shrub species. The semi-prostrate and tannin rich crowberry (Empetrum nigrum), showed the strongest recovery of all species, while the erect lingonberry (Vaccinium vitis-idaea) only showed weak signs of recovery. Thus, growth form determined the potential of plants to recover, whereas the trade-off between defensive investments and capacity to recover was weak or absent.

I studied the interaction between gray-sided voles and their main winter food plant, bilberry (Vaccinium myrtillus) on islands in and mainland sites close to the lake Iešjávri. I compared the abundance, population structure and palatability of bilberry ramets between vole-free islands, islands with voles but no predators and mainland sites with both voles and predators. Voles decreased the abundance of bilberry on the mainland, but the effect was much stronger on predator-free islands. Bilberry was fairly tolerant to grazing as it partially compensated for the lost tissue by producing more new ramets. Moreover, a cafeteria experiment showed that voles preferred the ramets from predator-free islands, which is inconsistent with conjectures emphasizing inducible plant defenses. The vole-bilberry interaction lacks features of delayed density dependence that could explain the vole cycles. I conducted a clipping and fertilization experiment to further investigate the effects of herbivory on palatability of bilberry shoots. Fertilization decreased the concentration of condensed tannins in shoots of bilberry and voles preferred fertilized and clipped shoots. I found no indication of induced defense that could reduce the palatability of bilberry twigs in response to herbivory.

The relationships between gray-sided vole densities, levels of invertebrate herbivory and chemical quality of leaves of Northern willow (Salix glauca) were studied on islands and mainland sites with contrasting vole densities. I found a positive correlation between level of invertebrate herbivory and vole density. The number of leaves per shoot, leaf size and leaf nitrogen content were also positively correlated with vole densities, while leaf C/N ratios were negatively correlated with vole densities. The positive correlation between vole densities and level of invertebrate herbivory is probably due to a facilitative effect of voles on invertebrate herbivores, mediated through changes in plant chemistry.

Place, publisher, year, edition, pages
Umeå: Ekologi, miljö och geovetenskap, 2006. 34 p.
Keyword
gray-sided voles, tundra vegetation, trophic cascades, plant-herbivore interactions, bilberry, plant communities, herbivory, plant resistance
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-794 (URN)91-7264-083-9 (ISBN)
Public defence
2006-06-01, Stora Hörsalen, KBC, Linneus väg 6, Umeå universitet, Umeå, 10:00
Opponent
Supervisors
Available from: 2006-05-10 Created: 2006-05-10Bibliographically approved

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