Effects of resource limitation on the physical and reproductive condition of sika deer on Nakanoshima Island, Hokkaido

Abstract

The physical and reproductive condition of introduced sika deer (Cervus nippon yesoensis Heude, 1884) on Nakanoshima Island (5.2 km 2 ) were studied during a 5-year-period.The population density increased from 31.5 deer/km 2 in 1980 to 57.5 deer/km 2 in the autumn of 1983, and declined the following winter to 26.3 deer/km 2 due to both natural mortality (22%) and removal (32%).As the population increased, availability of summer and winter forages rapidly decreased.Deer had eliminated dwarf bamboo by 1983, which was the most important forage in winter, and were forced to consume more bark and unpalatable plant species.In the winter of 1983-84, in conjunction with a longer snow cover than usual, a mass mortality (22%) from starvation was recorded.Although the body weights and skeletal size of island deer initially were almost the same as those of mainland deer, the 1984 animals of both sexes were smaller in body weight and chest girth than the 1982 animals.Sexual dimorphism in body weight and measurements (chest girth and hind foot length) became apparent only after 1.5-years-old in 1982, and after 2.5-years-old in 1984.Skeletal growth (jaw length and skull length) gradually declined in immature age classes with a higher population density.Antler growth, associated with the decrease in body weight, also decreased.The ratio of fawn to one-year-old or older females in autumn declined drastically from 65% in 1980 to 7% in 1984.Resource limitation caused by high population density, and fluctuating climatic conditions are the main factors that determined both the size of the individual deer and the population.