Geographical and seasonal variation of plant taxa detected in faces of Cervus nippon yakushimae based on plant DNA analysis in Yakushima Island

Recently, plant DNA analysis of feces has been successfully used to evaluate the food species composition of sika deer Cervus nippon. Here, we applied this method to Yaku-sika C. nippon yakushimae, which increased its population and had a great negative impact on understory vegetation in Yakushima Island. We identified food plants of C. nippon yakushimae by sequencing chloroplast DNA fragments (rbcL region) of plants remaining in feces collected in the field in April, June, August, and October 2018, using a next-generation sequencer. We collected feces from populations in two areas where populations have been managed by capture and three areas where those were not managed. The top two food plants in terms of the number of sequences determined were evergreen tall trees in all five areas. In addition to evergreen trees, understory herbaceous plants, including ferns, were included in the top 15 taxa in all areas. The diversity of food plants was higher in the managed areas than in the unmanaged areas. These results indicate that evergreen tall trees are the primary food plants of C. nippon yakushimae, but deer also forage on herbaceous plants as a side dish. Under this side dish effect, understory vegetation is reduced even under the high availability of food resources from tall trees. The high diversity of food plants in the managed areas suggested that understory plant diversity was restored when deer density was reduced by management.