Irruption of a Colonizing Sika Deer Population

Abstract

Irruptions of ungulate populations have been observed, but little is known of their cause of initiation and termination. We documented an irruption of a naturally colonizing sika deer (Cervus nippon) population on Cape Shiretoko, Shiretoko Peninsula, northeastern Hokkaido, Japan, and we examined limiting factors on population growth. The population increased from 54 deer in 1986 to 592 deer in 1998 (11 to 118 deer/km2, respectively) and declined to 177 (35 deer/km2) the following winter of 1999. The intrinsic rate of increase from 1986 to 1998 was 0.19 (95% CI: 0.16 to 0.22). We estimated an annual survival for adult females of 0.92. The ratio of calves to adult females was 76%. We observed a density‐correlated reduction in winter food resources. Density‐dependent food resources and their interaction with climatic factors were the most important limiting factors for sika deer. The population recovered rapidly following the population crash in 1999 and increased to 512 deer (102 deer/km2) in 2002. We anticipate further increase and a second crash. To confirm whether the population will be regulated naturally and to establish sika deer management policy in Shiretoko National Park, long‐term monitoring of the relationship between sika deer and their habitat must be implemented.

Deer herbivory affects the functional diversity of forest floor plants via changes in competition‐mediated assembly rules

“…Although it is difficult to practically compare the impacts of deer over/under-grazing on vegetation across regions, the level of the impacts on our plots may not have been as intense as these extreme cases. While the overabundance of deer has been a concern in the study region (Kaji et al 2004; The Forestry Agency of Japan 2007, 2012), the intensity of deer herbivory in our study site could be at a level that can, to some extent, maintain plant diversity (as explained by the intermediate disturbance hypothesis ;Grime 1973;Connell 1978). In other words, fencing has been affecting the understory plant communities in an adverse way by virtue of unnaturally excluding deer.…”

“…In Shiretoko National Park (located on the northeastern tip of Hokkaido, Japan), deer overabundance has resulted in numerous ecological issues, including negative impacts on forest understory plant communities (Kaji et al 2004;Mori et al 2015). To conserve forest vegetation, deer exclosure fences were established in the early 2000s, and since more than a decade has passed, we expect that the presence and absence of selective deer herbivory has considerably changed the biotic interactions among the plant species in these forests.…”

Adaptive management of sika deer populations in Hokkaido, Japan: theory and practice

“…Sika deer populations in Hokkaido are characterized by (1) a high intrinsic rate of increase (r m = 0.15-0.19; Kaji et al 2004), (2) no significant density effects on population growth until just before a population crash (Kaji et al 1988, and (3) a relatively simple life history (see ''Introduction''). Sika deer populations have fluctuated greatly due to heavy snow, overharvest, and bans on hunting in Hokkaido (Inukai 1952).…”

“…We have observed the irruption processes of two populations of sika deer in detail; an introduced population on Nakanoshima Island (NKI population; Kaji et al 1988) and a naturally colonized population on Cape Shiretoko (CS population; Kaji et al 2004; Fig. 8).…”

Effects of sika deer (Cervus nippon) and dwarf bamboo (Sasamorpha borealis) on seedling emergence and survival in cool-temperate mixed forests in the Kyushu Mountains

“…The difference in the impact of deer on S. borealis between the two sites was mostly due to the difference in the deer population density. Previous studies showed that the deer population density affects the extent of the impact on understory vegetation Values in parentheses are SDs (n = 10) (Tilghman 1989;Gill 1992b;Rooney and Walter 2003;Kaji et al 2004;Suzuki et al 2008). More seedlings emerged in the no-sasa forest than in the sasa forest (Tables 5, 6), even though there were fewer fallen seeds in the no-sasa forest.…”