Diet and diet preferences of introduced ungulates (Order: Artiodactyla) in New Zealand

Understanding the diet and diet preferences of introduced ungulates is a crucial step towards modelling their trophic interactions and managing their impacts. We collated information on the diet of 8 introduced ungulates (Order: Artiodactyla) from 19 studies in New Zealand. A total of 185 indigenous plant genera (379 species) was recorded as eaten. Five studies assessed diet choice by 4 ungulate species (red deer, fallow deer, white-tailed deer, and feral goats) in forests. Of the 60 plant species or genera present in two or more studies, 8 were always preferred (eaten more than expected from their availability) and 15 were always avoided (proportionately less eaten than was available); most others were not selected (eaten in proportion to their availability). From these data we constructed a table of preferences for commonly occurring forest plant species. Ungulates preferred woody species with low foliar lignin. Although there was no significant relationship between diet choice and foliar N, avoided species all had low foliar N. Ungulate preferences for fern species were closely related to foliar P concentrations, but not to foliar N concentrations. Since relatively few plant species were consistently preferred, we conclude that many native species have neutral resistance to ungulate herbivory, a conclusion that is contrary to the notion that the New Zealand flora is especially vulnerable to introduced herbivores.