Temporal changes in molar wear rate of a sika deer population under density-dependent food limitation

Negative effects of density-dependent food limitation on molar wear rate in ungulate populations, as well as unworn molar size and its sex differences in ruminants, have been studied for a long time. However, these studies were based on comparisons of populations from different districts or habitats. If drastic changes in food habits and life history occurred under density-dependent resource limitation, it is of great interest whether this change caused temporal changes in molar wear rate, and whether the degree of hypsodonty changed under this short but intensive selective pressure. We examined the temporal change in molar wear rate using long-term monitoring data of a sika deer (Cervus nipon) population on Nakanoshima Island, Hokkaido, Japan. Corresponding to the change in food habits, the molar wear rate changed mainly because of the amount of soil that was secondarily ingested when deer fed on fallen leaves. Molar wear rate was the fastest level after the first population crash on Nakanoshima Island among extant sika deer populations. Nevertheless, we did not find any evidence of increased hypsodonty in Nakanoshima deer. It is possible that natural selection for increased molar durability (hypsodonty) has been working on Nakanoshima deer, but the adaptive change has not yet appeared at a statistically significant level.