Changes in the population dynamics of Japanese serow and sika deer as a result of competitive interactions in the Ashio Mountains, central Japan

Comparison of food habits of sympatric animals provides understanding of interspecific relations. Previous studies of food habits of the two ruminants of Japan, sika deer (Cervus nippon) and Japanese serows (Capricornis crispus), have shown that sika deer are variable, and they are gazers in northern Japan, but browsers in southern Japan, whereas Japanese serows are browsers. However, these studies described the food habits of each species separately, and no study has compared the food habits of these species living in sympatry. Therefore, we examined these species on Mt. Yatsugatake, central Japan, using microhistological analyses and nutritional analyses of feces. Sasa nipponica, a dwarf bamboo, predominated in the fecal composition of sika deer, whereas both S. nipponica and dicotyledonous plants were found in the feces of Japanese serows. Crude protein levels of serow feces were higher than those of deer. The particle sizes of plant fragments in serow feces were smaller than those in deer feces, suggesting that serow fed more selectively on digestible plants than deer did. These results support the suggestions of previous studies conducted in different habitats and show that sika deer are less selective grazers, and Japanese serows are more selective browsers. Thus, food differences are likely explained by the feeding ecophysiology of the animals and not habitat differences.

At the landscape scale, localised culling is often conducted to achieve various deer management aims. However, few studies have assessed the effects of localised culling on deer population dynamics, owing to the spatially and temporally insufficient datasets of deer abundance that are derived from limited survey efforts. In this study, we estimated the population dynamics of a sika deer (Cervus nippon) population in the Tanzawa Mountains, central Japan, by Bayesian state-space modelling using spatiotemporally insufficient abundance indices and evaluated the effects of unit-specific culls on subsequent density changes in 56 units. The responses of deer density to unit-specific culls differed greatly among units, and a very weak correlation was observed between the intensities of unit-specific culls and the reduction in density. Deer populations in some units tended to resist density decreases despite high culling pressure, whereas those in other units were susceptible to density decreases with little to no culling pressure. Because the spatial scales of each unit were relatively small, annual density changes in each unit were largely influenced by deer movement in this estimation. The obscured effects of unit-specific culls, which were probably derived from deer movement among units in this case study, re-emphasized that deer migration should be incorporated into the planning of localised culling and that deer management should be coordinated over a wide area beyond landscape components and landownerships. Thus, we conclude that Bayesian state-space modelling is valuable for practical deer management programs at a large spatial scale even if different abundance indices are used.

Round bale silage is a widely used forage production system in Japan. In recent years, several suspected instances of damage to bales of round bale silage by sika deer were reported on a dairy farm in central Japan. We sought to confirm whether this damage was indeed caused by sika deer, and if so, when and how they caused the damage. We also analyzed the effects of possible covariates on seasonal and spatial variances in the incidence of the observed damage. Continuous monitoring using camera traps revealed that sika deer were responsible for the damage to the bales of round bale silage. The sika deer were observed to nibble at the surface of the bales of round bale silage after puncturing the plastic film used to promote anaerobic digestion of the silage. Several sika deer were responsible for damaging the bales of round bale silage, and the incidence of damage to the bales increased as snow cover increased in winter. Further, the incidence of damage to the bales of round bale silage was greatest farthest away from the center of the farm facilities, and farthest inside the wildlife protection area, which covered a large proportion of the farm. The findings clarified the extent of damage caused by sika deer to bales of round bale silage, and illustrated the need to prevent such damage throughout the country.

Haemadipsa japonica is a Japanese land leech that feeds on the blood of host animals, mainly the sika deer ( Cervus nippon ). The distribution of H. japonica has expanded since the 1990s, possibly due to sika deer population increases. Haemadipsa japonica populations were found in the northern and southern regions of Tochigi Prefecture, central Japan. Previous investigations reported that these populations are genetically differentiated between the north and south, although the sika deer distribution extends throughout the northern and southern regions. We hypothesized that the migration of sika deer might be limited, thus maintaining the two H. japonica genetic groups and restricting its range expansion. We evaluated this hypothesis by investigating the genetic structure of the mitochondrial DNA (mtDNA) and nuclear microsatellites (nSSR) of sika deer samples collected from Tochigi Prefecture and from H. japonica bloodmeal samples (invertebrate‐derived DNA; iDNA). The sika deer mtDNA presented two haplotypes (G‐ and A‐haplotypes) without a clear genetic structure. Conversely, the sika deer nSSR analysis indicated clear genetic differentiation between deer in the northern and southern regions, corresponding to the two H. japonica genetic groups. This indicates that sika deer movement is restricted to narrow regions in Tochigi Prefecture. Therefore, we conclude that the current H. japonica expansion in the prefecture likely depends on the migration of sika deer, only occurring within the northern and southern regions, even though this is driven by sika deer migration.

Simple SummaryInvestigating the interspecific interactions between species provides a suitable model for understanding the mechanisms of coexistence between sympatric species. We assessed the spatial and temporal partitioning of spaces between Japanese serows (Capricornis crispus) and sika deer (Cervus nippon), which are usually allopatric, in an area with early-stage invasion of sika deer into Japanese serow habitat. The habitat selection and activity patterns of the two species were evaluated using camera traps. Both species were recorded in >25% of the same camera sites and showed similar selection tendencies for water resources. The Japanese serows selected steep slopes, whereas the sika deer selected areas distant from human settlements, resulting in low spatial overlap. Additionally, the Japanese serows were more active during the daytime, whereas the sika deer were active at the crepuscule. The observed spatial and temporal partitioning likely reduces their encounter rates, thereby minimizing possible interference competition. However, spatial and temporal overlaps between the two species are likely to increase as the density of sika deer increases, potentially resulting in a decline in the density of Japanese serows with smaller body sizes. Trapping for deer management should be focused on areas with gentle slopes, away from valleys and human settlements, to reduce the unintentional capture of Japanese serows.The Japanese serow (Capricornis crispus) and sika deer (Cervus nippon) in Japan are usually allopatric. However, a recent expansion in the distribution range of sika deer, combined with an increase in abundance, has resulted in an overlap of the distribution ranges of the two species. We examined the habitat selection and activity patterns of Japanese serows and sika deer using camera traps placed at 83 sites within a 210 km2 study area, where the distribution range of these two species has recently overlapped. Although both species were photographed throughout the study area, we observed a low spatial overlap between them. The Japanese serows selected steep slopes, and the sika deer selected areas far away from human settlements. In addition, the Japanese serows and sika deer exhibited temporal partitioning with diurnal and crepuscular activity patterns, respectively. The observed partitioning could be explained by differences in their species-specific habitat selections, rather than competition, because the photographic capture rate of the Japanese serows was not affected by that of the sika deer and vice versa. These partitioning behaviors are likely to reduce the rate of encounters between the two ungulates, which enables their coexistence considering the sika deer density remains low.

Human ageing and population decline in Japan are causing agricultural field abandonment and providing new habitats for Japanese sika deer and wild boar. These species have expanded their distribution and increased in abundance across Japan and are causing increased agricultural damage. Effective countermeasures must factor in the behavioural flexibility of sika deer and wild boar. The aim of this study was to examine the effects of hunting and indirect human activities on the activity patterns of sika deer in central Japan and compare these with previous findings on wild boar. Camera traps were used to observe activity patterns of both species and that of humans. Sika deer and wild boar were most active at night during the non-hunting season. Hunting activities significantly reduced sika deer and wild boar activity patterns. In the non-hunting season, nocturnal activity of sika deer increased with decreasing distance to settlement. A similar, but weak response was also observed for wild boar. This study suggests that sika deer and wild boar avoid humans and human-dominated areas by being nocturnal. The recent introduction of night hunting might help to control wildlife populations, but monitoring will be necessary to confirm this expectation.

Quantitatively estimating herbage damage caused by wild herbivores, such as deer, provides a basis for developing countermeasures designed to prevent the damage. However, a simple and easy way to quantify deer damage has not yet been developed. In this study, we estimated herbage damage caused by sika deer (Cervus nippon) in three meadows of a dairy farm in central Japan during three cutting periods. We then compared the validity of quantitative estimation of herbage damage using three simple methods: by comparing plant height or plant length outside and inside a deer exclosure cage, and by estimating the density of sika deer populations using spotlight census surveys in the meadows. We also examined the effect of the timing of herbage damage (i.e. early, middle and late season) caused by sika deer on a total herbage yield during each cutting period. The decreased plant height outside of a deer exclosure had a significant and unbiased linear relationship with herbage damage caused by sika deer. However, the decreased plant length outside of a deer exclosure had a significant but biased linear relationship with herbage damage caused by sika deer. The required sample size for assessing the difference in plant height outside of a deer exclosure increased when the herbage damage was small. On the other hand, the mean density of sika deer did not have a linear relationship with herbage damage. The timing of herbage damage caused by sika deer did not significantly affect total herbage yield. These results show comparing plant height outside and within a deer exclosure provides a simple and inexpensive quantitative method that can be used to estimate herbage damage caused by sika deer. This simple method, however, can be reliable when the herbage damage is relatively large (e.g. >30%).

Diet reconstruction using mesowear analysis has mainly been applied to extinct species and their paleoenvironments. Little is known regarding the effects of dietary differences on sympatric environments using this analysis and the limited existing knowledge from extant species may introduce errors when applied to fossil assemblages. I aimed to determine the sensitivity of mesowear analysis using extant ungulates with known diets. An interspecific comparison was conducted using wild populations of Japanese serow (Capricornis crispus, n = 37) and sika deer (Cervus nippon, n = 55) living in deciduous broad-leaved forest of the Nikko National Park, central Japan. One of the mesowear variables differed significantly between the two species (Fisher's exact test: p < 0.05). According to hierarchical cluster and principal component analyses, Japanese serow were classified as browsers, while sika deer as mixed feeders. Previous studies support these results; therefore, mesowear analysis can be used to detect dietary differences in sympatric species.

Dental microwear texture analysis (DMTA) can be used to quantitatively evaluate tooth surface roughness and has been used to distinguish herbivorous ungulates according to interspecific dietary differences among grazers, browsers, and mixed feeders. Moreover, DMTA has been applied among local populations with intraspecific dietary variation. In general, the tooth surfaces of grazing species/populations are rough, whereas those of browsing species/populations are smooth. Whether DMTA can be used to detect dietary differences among sympatric species is of interest. In the present study, we aimed to use DMTA to explore interspecific differences in diet between two ruminants in Japan—the sika deer and Japanese serow in Nagano Prefecture. We found significant differences in surface roughness parameters between deer and serow. The tooth surfaces of the deer were more undulated with parallel scratches, whereas those of the serow were smoother with pits. These results indicate that the deer consumed abrasive graminoids more frequently than the serow, which is in accordance with previous dietary analyses. However, the two species did not segregate dichotomously but showed a huge overlap in DMTA parameters, implying dietary overlap. The present study shows the potential of DMTA to clarify the foraging ecology of sympatric ruminants from skeletal specimens.

The diel activity pattern is a key factor in the coexistence mechanism of sympatric wild animals, enabling temporal niche partitioning. Although previous studies on sympatric ungulates (sika deer, Japanese serow, and wild boar) have reported dietary and spatial niche partitioning, temporal niche partitioning in these sympatric ungulates is not well understood. In this study, we aimed to elucidate the seasonal diel activity patterns of three sympatric ungulates in Gifu Prefecture, Japan, where they have been sympatrically distributed since 1978. We placed 21 camera traps from August 2017 to November 2019, and investigated diel activity patterns and photographic frequencies over three time periods (daytime, night-time, and twilight). Although we found no seasonal changes in diel activity patterns of three ungulates, but patterns showed differences among species. While sika deer showed crepuscular activity, wild boars and Japanese serows showed nocturnal activity. In addition, Japanese serows showed temporal niche partitioning against sika deer. Consequently, we suggest that the relationship between sika deer and Japanese serow is competitive in terms of diel activity patterns.

The negative impacts of sika deer (Cervus nippon) on Japanese serows (Capricornis crispus) are a subject of concern in the mountainous regions of Japan. To develop a methodology to collect information with regard to the abundance and habitat selection of sympatric large mammals using drones (unmanned aerial vehicles; UAVs) equipped with thermal infrared and red‐green‐blue (RGB) sensors, surveys were conducted at night and in the early morning in a high mountainous habitat. Despite the similar size and shape in thermal infrared images for sika deer and Japanese serows, species identification based on body color using RGB images was possible during the period from dawn to early morning. The UAV surveys also revealed the large abundance of deer (&gt;40 deer/km2) and suggested different habitat selection between deer and serows in the alpine grassland. Our results were the first snapshots of sympathetic deer and serow distribution. UAV surveys using both thermal infrared and RGB sensors in early morning could be useful for research and monitoring of large mammals in open areas, such as grasslands, marshlands, high mountains, farmlands and drylands.

Age-specific changes in deer demographic parameters under food limitation are an important factor in predicting the post-population-crash dynamics of irruptive deer populations. To evaluate the differences in age-class-at-death between the initial irruption and post-population-crash phases of a sika deer (Cervus nippon) population, we analyzed a dataset of naturally dead carcasses from an introduced sika deer population on Nakanoshima Island, Japan. We predicted that the occurrence probability of fawn-class sika deer carcasses would increase in the post-population-crash phase and that the occurrence probability of old-class sika deer carcasses (≥ 10 years old) would decrease during this phase. Contrary to our expectations, the relative occurrence probabilities of four age classes [fawn, yearling, prime-aged (2–9 years old), and old] of sika deer carcasses did not differ between the initial irruption and post-population-crash phases. This could partially be a side-effect of classifying deer age into just four categories; slight changes within the age classes could not be detected because of this statistical limitation. Comparative studies are required to determine whether these results coincide with other irruptive deer populations.

In coevolved native ungulate assemblages, the mechanisms underlying competition remain unclear because, to date, little direct evidence of competition exists. In high‐elevation areas in Japan, the number of native Japanese serows (Capricornis crispus) has been decreasing as the number of native sika deer (Cervus nippon) increases. Here, we assessed the effects of deer on vegetation, vigilance and foraging behavior, physiological stress, and relative abundance and ratio of young individuals of serows throughout the warm season across two study sites with different deer densities and similar landscapes in high‐elevation areas of Mount Asama, Central Japan. The abundance and diversity of palatable forage for serows (i.e., herbaceous forbs) were significantly lower in areas with abundant deer, suggesting that deer abundance reduced the vegetation quality for serows. Serow vigilance rate was significantly greater in areas with abundant deer, suggesting that the increased probability of encountering deer or of intraspecific aggression increased vigilance. Serow bite rate was significantly lower and their step rate was greater in areas with abundant deer, suggesting that lower availability of herbaceous forbs and higher vigilance reduced serow foraging efficiency. Levels of serow fecal cortisol metabolites were significantly greater in areas with abundant deer, suggesting that deer abundance and decreased foraging efficiency increased physiological stress of serows. The relative abundance and ratio of young individuals of serow populations were significantly lower in areas with abundant deer, suggesting that deer abundance negatively affected the serow population through both exploitative and interference competition. This is a rare case to show direct evidence and mechanisms of interspecific competition in native ungulate assemblages. Human alteration of ecosystem processes, such as the elimination of top predators and decreased human hunting pressure on deer, may determine changes in ecological relationships between serow and deer.

Diet compositions of two sympatric ungulates, the Japanese serow (Capricornis crispus) and the sika deer (Cervus nippon), in a montane forest and an alpine grassland of Mt. Asama, central Japan

Two ruminants, sika deer (Cervus nippon) and Japanese serows (Capricornis crispus), inhabit the Japanese archipelago. The range of sika deer includes nearly the entire archipelago from Hokkaido to Kyushu, including habitats from the coastal zone to the montane zone. In contrast, the distribution and the habitat of Japanese serows are limited: they inhabit deciduous broad-leaved forests from Honshu to Kyushu (Ohdachi et al. 2009). These two ruminants occur in sympatry in some localities. Information on such cases would help to document how two animal species within the same guild can share a common food supply. However, only one study at Mt. Yatsugatake, central Japan, has compared the diets of sika deer and serows (Kobayashi and Takatsuki 2012). Their study demonstrated that sika deer subsisted on dwarf bamboo, whereas serows mainly fed on forbs and browses (Kobayashi and Takatsuki 2012). The diet compositions of the two species were more similar in winter, likely because food was limited and both ungulates were forced to feed on similar food plants (Kobayashi and Takatsuki 2012). Although it is known that there are many more sympatric populations of these two ruminants, no other studies have been done. Further, quantitative food analyses of Japanese serows are limited, and no study has been done for southern serow populations. The present study, therefore, compares the diets of sympatric populations of these two ruminant species in the eastern part of Shikoku, an island in western Japan, representing