2020 Volume 37 Issue 2 Pages 101-107
We monitored the deer grazing pressure on a population of an unpalatable perennial, Primula japonica in a long-term grazed habitat by sika deer, using an enclosure treatment with cages for two years. The two-year census showed that all unenclosed individuals of this species lost their aboveground parts due to grazing, whereas all enclosed individuals survived and most of them elongated inflorescences at the end of the census period. Although inflorescences extended outside cages, no grazing on the reproductive organs was observed. We also quantified the main chemical compound of the species using the gas chromatography and evaluated variations in the concentration of the compound among regions (a high deer-density site and a low deer-density site) and among organs (leaves and inflorescences), which identified flavone as the main compound and detected a higher flavone concentration in flowers than in leaves but little difference among regions. Although the results showed a possibility that flavone can contribute to protecting reproductive organs from deer grazing, we could not demonstrate clear evidence that flavone has toxic effects on deer. Future studies need to evaluate whether deer also graze other unpalatable plants in high-deer density regions and to verify mechanisms on how sika deer can overcome the chemical defence of unpalatable plants.