Spatial and temporal variation in the diet of introduced sambar deer (Cervus unicolor) in an alpine landscape

Context. In south-eastern Australia, the abundance and distribution of non-native sambar deer (Cervus unicolor) has increased dramatically in alpine environments. As a result, significant concern surrounds the potential for the species to impact rare plant species and vegetation communities through browsing.Aims. We aimed to determine the diversity of the plant species eaten by sambar deer in the Alpine National Park and to understand any spatial and temporal variation in deer diets.Methods. We collected 90 sambar deer faecal pellet samples over a 3-month flowering period across two contrasting study sites with differing elevation, vegetation and underlying geology. We performed DNA sequencing using the ITS2 gene region and assigned dietary items to the lowest taxonomic level possible. The frequency of occurrence and sequencing read depth of each dietary item was calculated to investigate the diet of sambar deer at spatial and temporal scales, and dietary preferencing was assessed by comparing the frequency of occurrence of dietary items to the observation records for each dietary item in the study area.Key results. We detected a total of 369 unique plant Operational Taxonomic Units (OTUs) from sambar deer faecal samples, representing 35 families and 80 genera. Considerable variation in the diet was observed over small spatial scales, and evidence of temporal diet variation was noted in one of the study sites. We detected Silky Snow-daisy (Celmisia sericophylla), which is currently listed as critically endangered under the Victorian Flora and Fauna Guarantee Act 1988, and Hawkweed (Pilosella spp.), a highly invasive, non-native taxon that is sparingly established in Alpine ecosystems.Conclusions. Sambar deer displayed an intermediate feeder behaviour in alpine environments, foraging on a variety of forbs and shrubs, but forbs were the dominant dietary items. The spatial variation observed in the diet of sambar deer suggests that individual deer are unlikely to be dispersing widely while foraging.Implications. Our results emphasise the need for careful evaluation of sambar deer impacts within individual sites and at small spatial scales. The detection of species of conservation significance in the diet indicates that the presence of sambar deer should be considered a significant risk to biodiversity in areas of high conservation value.