Fcompetitive Interactionsintheashiomountains
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Association ofofWUdlifeand Wildlife and Human Society - Biosphere Conservation 2 (1) :35 44. 1999 Changes in the dynamics ofJapanese serow and sika deer as a result opopulationf competitive interactions in the Ashio Mountains, central Japan Masaaki Koganezawa Utsunomtya Uhiversity 1lorests hacutty ofAgricutture, Utsunomlya U}tiversiC}; Z556 funyu, Shiqya-machi, Shiqya-gun, lbchigi 329-2441, Jbpan Abstract Changes in the population dynamics ef the Japanese serew Capricornis crispus and the sika deer Cervus nippon were studied in the Ashio Mountains ofNikko National ParK [[bchigi Prcfe¢ ture, Japan, from March 1982 to December 1995. Although the geographical distributions of the two species overlap in many areas ofJapan, wherever the snow is not deep, Japanese serow and sika deer are usually found living allepatrically. In Ashio, however, they occurred sympatrically, but their populalions have changed drastically and they have segregatecl during the 1980s and 1990s, l propese two factors that may contribute to their shift from sympatry towards an allopatric existence. The primary contributing factor may be the overlap in the food habits of the twe species. Japanese serow were found to feed on the leaves ofdeciduous trees and herbaceous shrubs during the summer, while in winter they feed mainly on the needles ofconiferous trees. In contrast, sika deer were found to feed mainly on graminoid species year reund. On]y in severe winters did the deer extend their diet to include the needles ofconif- erous trees, and the twigs and bark of deciduous trees. During such winters their diet then overlaps that of the serow, and this oyerlap may result in a rapid depletion oflimited food supplies. The deer. with their more flexible dietary habits may be better able to telerate such poor foraging conditions, whereas the serow may suffer from an unbal- anced diet and face a deficiency of food thus forcing them to move away from areas where deer are present. A secondary cause may be the increased interactions between the species, Serow are tenitorial and essentially solitary, and so are presumed to be sensitive to both intra- and inter-specific crowcling, whereas sika deer are not territorial, occur in herds and are usually very toierant of other animals, In order to ayoid encounters with sika deer, the sensitive serow may emigrate from areas with high deer population densities. This competitivelavoidance relatien- ship between the Japane$e serow and sika deer may help to explain why the two species generally occur allopatri- ca]]y in Japan. Key words: competitive interaction, food habit, Japanese serow, population dynamics, sika deer INTRODUCTION cuT), the area of spatial overlap of these species is about 20%. Even in areas of local overlap, the species are areas The Japanese serow Capricornis crispus, a moun- usually allopatric; with few serow occurring in tain dwelling ungulate, is distributed throughout with high deer densities, such as at Mt. Geyo, Nikko, Honshu, Kyushu and Shikoku islands; its habitat in- [[hnzawa,Nishi-yatsugatakeandOhdaigahara.Therea- cludes both warm-temperate and cool-temperate for- sons for this spatial segregation have not yet been iden- ests. The distribution of the sika deer Cervus nippon tified. In Ashio, adjacent to Nikko, in central Honshu, overlaps that of the serow, except in heavily snow- both species lived sympatrically. During the 1980s coveTed areas. Sika deer are unable to tolerate snow and 1990s, howeveT, drastic changes in both species depths of more than 50 cm, and tend to avoid aTeas numbers and distribution have occurred, and segrega- with fifiy days or more of such deep snow (Tbkida et tion has occurred. al. 1981, Maruyama 1981). In the main islands ofJa- The objective of this study was to assess the possi- pan, except Hokkaido (wheTe the seTow does not oc- bility that competitive interaction might be occuning 35 NII-Electronic Library Service Association ofofWUdlife Wildlife and Human Society Biosphere Conservation 2 <1), 1999 N Mt. Mt STUDYAREA l O 5 10km LFig. - 1. Location of the Ashio study area (November 1983 November 1991) including the Matsuki-zawa, Kuzo-zawa and Akakura obscrvation sites in Nikke National Park, central Honshu, Japan. between the two species, through an ana]ysis of their August (based on data gathered at the Nikko VVeather population dynamics, theiT food habits and their inter- Station, 1944-1996). The average annual precipita- specific social tendencies. tion was 2,230 mm, with snowfall varying with eleva- tion. Little snow accumulated below 600 m, whereas STUDY AREA at around 1,200 m snow averaged 30 cm in depth thToughout the winter during the study period. In the was This study conducted from March 1982 to unusually severe winter of 1983-1984, snow accumu- December 1995 in the Ashio Mountains in Nikko lated to a depth of 120 cm, but that was exceptional National Park, Tbchigi Prefecture, situated approxi- (Fig. 2), Severe winters, with heavy snow, also oc- mately 100 km north of [Ibkyo (Fig. 1). The average curred in both 1990-1991 and 1991-1992. rnonthly temperature at Chugushi, which is situated at The study aTea is complex with rugged terrain, Due 1,292 m, just seven kilometres north-east of the study to past copper-mining activity and forest fires, most -4,4eC OC area, ranged from in FebiuaTy to 18.4 in (75%) ofthe natural vegetation has been lost and this 36 NII-Electronic Library Service Association ofofWUdlife Wildlife and Human Society Biosphere Conservation 2 (1), 1999 so7esot 50i 40Ian 3020too 19e2-83 19S3-S4 tgS4-S5 ri9e5-S6 19e6 1987 lgSB 19S9 1990 1991 1ss2 1993 t994 t995 ･e7 ･Be ･e9 -90 -91 -92 -93 -94 -95 ･96 Fig. 2. Number ef duys with snowfall over 20 cm and 50 cm in Chugushl (1,292 m altitude), 7 km north-east of the study area, between 1982-1996. resulted inheavy erosion between the 1890s and the pseudo-acacia forest growing close to the village. 1960s. At present, Miscanthus sinensis grasses, herbs suchasRaynoutriajaponicaandAtiryriumyokoscense, METHODS and brush such as Clethra barvinervis,Robinia pseudo- acacia, and Pinus thumbergii, have been planted to Serow were counted with binoculars (x 8) and tele- facilitate ecosystem recovery, scopes (× 20, x 40) usually at a distance of 500 m of the The populationdynamics both Japanese se- (ranging from 150 to 750 m) while scanning opposite row and the sika deer were studied in three study ar- slopes across valleys, Observations weTe made dur- eas on the slopes of the Ashio Mountains. These were ing the daytime on three consecutive days in April and at Kuzo-zawa (64 ha) and Matsuki-zawa (84 ha), which December each year from 1982 to 1995, Each serow were studied from 1982 to 1995, and at Akakura (125 was individually identified on the basis of its distinc- ha) which was studied from 1992 to 1995 (Fig. 1). tive physical features, resulting in an actual count of These s]opes are very steep, measuring 30-40 degrees. serow present within the study area. Kuzo-zawa is located in the centre of the study area Sika deer were also counted on the same days and and Tanges from 700 m to 1,200 m in elevation, Re- on the same slopes as the serow. When counting sika planting was begun on this slope in 1956, and the veg- deer, each study area was divided into three units, each etation now consists of young pines, deciduous bToad- of20-30haeach,withoneresearcherassignedtowatch leaved bushes, and Miscanthus grasses. Matsuki-zawa, each unit. Counts were macle six times each day, at which ranges in elevation from 900 m to 1,500 m, is hourly intervals, over the three consecutive days in located four kilometres west ofKuzo-zawa. Re-plant- April and December from 1983 to 1995 and in Febru- ing was begun on this slope in 1970, and most of this ary 1991. Sex, age, and group size were recorded at s]ope now consists of Afiscanthus grasses and bare each count, and times, locations and directions of rocky Akakura, which ranges in elevation ground. from movement were plotted on maps (1:5,OOO), Tlie maxi- 600 m to 1,200 m, is located two kilometres south of mum number of deer observed during the six counting Kuzo-zawa and is a[ljacent to a vi]lage. Re-planting periods for each of the three days was averaged and of this slope began in the late 1970s, and the vegeta- used as a density index for each study area. tion now consists of a thin cover ground of the herb The food habits of the Japanese serow and the sika Athyrium which grows on rocky ground, with Robinia deer were determined using two methods, Direct ob- 37 NII-Electronic Library Service Association ofofWUdlife Wildlife and Human Society BiosphereCon$ervation 2 (1), 1999 40 so 2o 10 o50 19S2 19S3 lgB4 lgeS t9S6 19e7 198e t9e9 1990 1991 1992 lg93 1994 1995 MATUKI-ZAWA roNEMxas-as- 3eit:1h Sikadeer ' 2e=-utEoa // --Y- --- le Ar" }V- x sor il/VvVlle-."...---- o lg62 19e3 19B4 t985 19B6 19e7 198e 19B9 1990 lg9t t992 1993 1994 19g5 2o AKAKURA 10 o 19B2 1ce3 19B4 Fig. 3. Density of Japanese serow and sika deer in the Ashio Mountains, central Japan, between 1982 and 1995, based on early spring and early winter counts. (Solid dots = Japanese serow; open dots = sika deer.) servations were made ofthe food items eaten, and the eas and at the same time as the serow. In the case of stomach contents of culled animals were analysed. sika deer, however, it proved impossible to individu- all Direct observations were made of the feeding habits ally identify all the food items being selected by ofJapanese serow in Akakura between April 1993 and the animals foTaging, so data were recorded every 15 the of May 1994, and in Kuzo-zawa between May and De- minutes.