Influence of foliar traits on forage selection by introduced red deer in New Zealand

Abstract

Predicting the diet of large mammalian herbivores is difficult due to the many factors at multiple scales that influence diet selection. One approach to understanding diet selection is to relate diet choices to the foliar and structural traits of forage species. Using data on diet selection by red deer ( Cervus elaphus scoticus) in Fiordland National Park, New Zealand, we determined the extent to which interspecific differences in the palatability of 46 plant species could be explained by 11 chemical and structural characteristics of plant foliage. Woody species were more palatable to deer than non-woody species (mostly ferns) and palatability declined with increasing concentrations of foliar cellulose. High concentrations of cellulose in fern leaves may increase toughness and resistance to tearing by herbivores, thus contributing to the low palatability of these plants. When two species that were consumed only in the winter were removed from the analysis, palatability was also negatively correlated with phenolic content. High phenolic concentrations may deter herbivory in summer, when forage with low phenolic concentrations is available (e.g. herbaceous dicots), whereas deer may have little choice but to consume species rich in phenolics during winter, when less forage is available. The relatively high concentrations of phenolics in our dataset compared to other floras, despite the absence of large native mammalian herbivores in New Zealand, suggest that these compounds are multifunctional.