Leaf trait-palatability relationships differ between ungulate species: evidence from cafeteria experiments using naive tussock grasses

Leaf functional traits have been proposed as general indicators of plant palatability to ungulate herbivores, identifying which species are likely to be most at risk from ungulates, and how ungulate grazing may change ecosystem processes. However, few studies have tested whether leaf trait–palatability relationships are consistent across different ungulate species. The palatability of 44 native New Zealand grass taxa (from the genera Festuca and Chionochloa) to two ungulate herbivores (sheep Ovis aries and red deer Cervus elaphus scoticus) was assessed in cafeteria experiments. There were significant differences between sheep and deer in the selection or avoidance of grass taxa, in part related to differences in response to variation in leaf functional traits. Deer had a greater tendency than sheep to select grasses with a higher specific leaf area (SLA) and to avoid taxa with a low SLA, suggesting that it is not possible to generalise leaf trait–palatability relationships across different ungulate species. Results suggest different ungulate species are likely to have additive effects on the biodiversity and ecosystem functioning of New Zealand’s native grasslands. These findings indicate that the impacts of ungulate herbivory on ecosystem processes will depend on which grass species are present.