Factors explaining the extension of the sika deer's range in Nikko, Japan
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The geographical distribution, density and population composition of sika deer <i>Cervus nippon</i> were studied in Nikko National Park, central Honshu, Japan. Deer density, distribution, age-sex structure, and group size were investigated along five sampling routes ranging from a traditional wintering area at Omote Nikko, to the distributional limit at Oku Nikko, from April to December 1995. Dry standing biomass, culm and leaflengths of <i>Sasa nipponica</i>, the major food species of sika deer, were measured by harvesting a total of 80 1 × 1 m plots along the same five sampling routes. The Nikko sika deer population began to irrupt, extending its distribution, after a mass die-off during winter 1984. The availability of food resources for sika deer has improved in the region due to the decrease in snow accumulation as a result of climatic warming, this has led to an increase in the environmental carrying capacity during winter. In the traditional wintering area, <i>S. nipponica</i> was dwarfed under the high grazing pressure of sika deer, as a result its standing biomass decreased, and deer density was lower. More females and calves occupied the new and traditional wintering grounds than in the frontier area at Oku Nikko. In these wintering grounds, males occurred at very low densities, except for during the rutting season. During the non-rutting season, males inhabited the frontier area of the summer range and/or the outer area of the wintering grounds, and sex segregation was observed in these areas. From the traditional wintering ground to the frontier area, the ratio of juveniles to adult females increased, while the opposite was true for the calf to adult female ratio. The establishment of a new wintering area in a previously snowy area can be expected to provide a base from which sika deer will be able to establish further wintering grounds in future. As global warming continues, the Nikko sika deer population may further extend and enlarge its range into the surrounding areas.
- Biosphere conservation : for nature, wildlife, and humans
Biosphere conservation : for nature, wildlife, and humans 3(2), 55-69, 2001
Association of Wildlife and Human Society