Evol Ecol Res 11: 1205-1216 (2009)     Full PDF if your library subscribes.

Plant defences at no cost? The recovery of tundra scrubland following heavy grazing by grey-sided voles, Myodes rufocanus

Jonas Dahlgren1,2, Lauri Oksanen3,4, Johan Olofsson1 and Tarja Oksanen1

1Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden,  2Department of Forest Resource Management, Swedish University of Agricultural Sciences, Uppsala, Sweden,  3Department of Biology, Section of Ecology, University of Turku, Turku, Finland and  4Department of Natural Sciences, Finnmark University College, Alta, Norway

Correspondence: L. Oksanen, Department of Biology, Section of Ecology, University of Turku, FI-200 14 Turku, Finland.
e-mail: lauoks@utu.fi


Background: Evergreen ericaceous dwarf shrubs form a dominating component of low arctic and low alpine vegetation. They typically produce high contents of secondary chemicals such as phenolics. The primary function of these chemicals may be to defend the shrubs by making them less palatable to herbivores.

Question: Does the production of secondary chemicals carry a fitness cost in terms of low growth rate and, therefore, low capacity to recover from past herbivory?

Methods: In 2000, we constructed vole-proof exclosures on low arctic islands where vegetation had, since 1991, been heavily impacted by grey-sided voles. In 2000 and 2003, we surveyed the vegetation of the exclosures, of unfenced plots on the same islands, and of control plots on a vole-free island. We used the point-frequency method for vegetation surveys.

Results: In the exclosures, the biomasses of most plant species increased, by and large, at the same pace. The two woody species, which increased most rapidly, were the maximally palatable bilberry (Vaccinium myrtillus) and the phenolics-laden, maximally unpalatable northern crowberry (Empetrum nigrum ssp. hermaprhoditum). The recovery rates of these species were similar.

Conclusions: The high concentrations of phenolics typical for evergreen arctic dwarf shrubs do not carry any obvious cost in the form of reduced capacity for compensatory growth. The principle of trade-offs does not help to explain the variation in plant palatability.

Keywords: arctic, herbivory, multiple benefits, Myodes rufocanus, resistance, tolerance, trade-offs, tundra, vegetation recovery, voles.

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