Ratite and ungulate preferences for woody New Zealand plants: influence of chemical and physical traits

Abstract

Ratites (ostriches Struthio camelus) and ungulates (red deer Cervus elaphus scoticus and goats Capra hircus) were presented with 14 indigenous shrubs in cafeteria style trials. The shrubs represented the spectrum of woody plant architecture, ranging from broadleaved monopodial species through to small-leaved highly branched divaricates. Trials were stopped when almost all shoots of the plant expected to be most preferred had been consumed. There were considerable differences between the herbivores in their selection of certain plant species. Aristotelia fruticosa was avoided by deer, neutrally selected by goats, and preferred by ostriches. All herbivores strongly avoided two species, Pseudopanax crassifolius and Coprosma rugosa. Analysis of relative offtake (proportion of biomass consumed from each species, relative to total biomass consumed) showed that all three herbivores ate less of species with small leaves. Consumption by all herbivores was reduced by structural plant traits (i.e. divarication and related attributes) more than by chemical plant traits. The immediate impact of browsing on the plants, measured as the rank of proportion of shoots eaten, was broadly similar across the herbivores. The broadleaved species (e.g. Myrsine australis, Aristotelia serrata) experienced the greatest browsing, while divaricate (e.g. Coprosma rugosa) and conifer species (e.g. Podocarpus hallii) were generally least browsed. Although cafeteria-style experiments have limitations, our results for deer broadly correspond to those of field-based diet preference studies.