The Effect of Fertiliser and Shading on Plant Chemical Composition and Palatability to Orkney Voles, Microtus arvalis orcadensis

Abstract

This study investigated the effect of environmental factors on plant allocation to secondary compounds, and whether differences in these allocations between individual plants explained the selection behaviour of mammalian herbivores. Sitka spruce (Picea sitchensis) seedlings and heather (Calluna vulgaris) plants were subjected to fertiliser and shading treatments which altered their nutrient and secondary compound content. The response of Orkney voles (Microtus arvalis orcadensis) to these treatments was tested in laboratory feeding trials. Foliage from the spruce seedlings which had received both shading and fertiliser were the most palatable to voles. This preference correlated with the effects of the treatments on seedling nitrogen and phenolic levels, but not with monoterpene content. Heather which had been fertilised was also the most preferred, but in this case the chemical basis for palatability was nitrogen and fibre content as the phenolic content of the plants was not altered by the treatments. This study shows that predictions of the carbon/nutrient balance hypothesis for allocation to plant defences are not applicable to all groups of secondary compounds, or to all plant species, and that voles are capable of using a variety of chemical cues to detect environmentally induced differences in the nutrient quality of individual plants within a species