Study area

Nearly 70% of Aomori Prefecture is covered by cool-temperate forests (Figure 1) composed of mainly beech and oak (Quercus crispula Blume) trees as well as coniferous plantations of Japanese cedar (Cryptomeria japonica D.Don) and Japanese larch (Larix kaempferi Carr.). Since most of these forested areas are mountainous, human settlements are concentrated in the narrow flatlands along rivers. The area is in the cool-temperate climatic zone. Mean air temperature and annual precipitation in 2009 were 10.6° C and 1,177 mm, respectively (Japan Meteorological Agency 2010). The period of snowfall was from early December to late March, with a maximum snow depth of around 2 m in lowland forested areas and 3–5 m in mountainous forested areas. Lingering snow was observed until late May.

Seven species of medium- and large-sized mammals—Japanese serows, Japanese martens (Martes melampus Wagner), raccoon dogs (Nyctereutes procyonoides Gray), Japanese badgers (Meles anakuma Temminck), Japanese weasels (Mustela itatsi Temminck), red foxes (Vulpes vulpes Linnaeus), and Japanese hares (Lepus brachyurus Temminck)— have ranged throughout the prefecture (Biodiversity Center of Japan 2010). However, past overhunting and human destruction of native forests caused the extinction of populations of gray wolves (Canis lupus Linnaeus), sika deers (Cervus nippon Temminck), and wild boars (Sus scrofa Linnaeus) in this prefecture, and the distributions of Japanese macaques and Asiatic black bears are still fragmented and isolated (Mito 1992, 1997; Tsujino et al. 2010).

Study animals

Dung beetles are classified as part of the superfamily Scarabaeoidea and use animal excrement and carcasses as food or oviposition resources. Thus far, 152 species and 9 subspecies of indigenous dung beetles have been confirmed in the Japanese archipelago (Kawai et al. 2005). Dung beetles are generally divided into 3 groups according to nesting strategy: tunnellers, dwellers, and rollers (Cambefort and Hanski 1991). Most dung beetle species inhabiting Japan are classified as tunnellers or dwellers (Kawai et al. 2005).

In the past, scientific literature regarding the ecology and society of forest dung beetles in the cool-temperate zones of northern Japan has been limited. Recently, however, Enari et al. (2011) evaluated the community structure of dung beetle species using the feces of Japanese macaques in similar study areas. They confirmed (1) the presence of 14 dung beetle species comprising 8 dwellers and 6 tunnellers, and (2) that the frequency of occurrence of every beetle species was high in spring and low in autumn.

Dung beetle sampling

Dung beetles were sampled using baited pitfall traps in spring (mid-June; i.e., soon after the snow melted) and summer (mid-August; i.e., the warmest period) 2009, but not in autumn and winter, which are the inactive seasons for dung beetles in cool-temperate forests (Enari et al. 2011). The traps were set in the following 3 sites within the study area: the southern Tsugaru Mountains (TM), which are classified as a Special Protected Zone of a Wildlife Protection Area; the southeastern Hakkoda Mountains (HM), which contain national parks with Special Zone Protection status; and the northeastern Shirakami Mountains (SM), where primary forests are listed as a World Nature Heritage site by UNESCO (Figure 1). These 3 sites are commonly covered with undisturbed beech forests, but compositions of large mammalian species are different today than they were historically (Table 1). Mean elevation and mean canopy openness, calculated using CanopOn 2.03 (Takenaka 2009) with hemispherical photographs, are about the same among the 3 sites (Table 1). Mean air temperature during the study period ranged from 14.5 to 17.2° C in spring and from 20.2 to 23.0° C in summer (Table 1).

Four parallel 40-m line transects at 20-m intervals were established at each site, and 5 sampling points at 10-m intervals along each transect were set. Then, pitfall traps, made from plastic containers (14 cm in diameter and 10 cm deep) and plastic cups (8 cm in diameter and 5 cm deep), were set at each sampling point. Trap design was based on that of Enari et al. (2011). Each container holding 50% ethylene glycol (used as a preserving fluid) was buried to its rim in the ground, and the cup was hung by a wire in each container. A sample of fresh feces (15 g) from each one of 4 mammals—Japanese macaques, Asiatic black bears, Japanese serows, and cattle—was placed into the cups equipped in the respective trap sets along the transect (i.e., 5 traps per each mammal feces at every site). To acquire fresh feces from wild macaques, macaque troops in the area around the SM study sites were followed. Fresh feces from wild bears were acquired from bears that were captured in box traps in the same area. Serow feces were collected from a neighboring zoo because of the difficulty in accessing fresh serow feces. Fresh cattle feces were obtained from a nearby cowshed. The feces samples were homogeneously mixed for use in the pitfall traps. A preliminary examination of the contents of each mammalian feces using the point quadrat method (Stewart 1967) showed variations among different mammal feces and seasonal changes, except in cattle feces (Table 2).

Figure 1.

Map of the study area in the northernmost part of mainland Japan. The 3 black squares (SM, TM, and HM) on the map indicate the study sites where baited pitfall traps were set. The sites were in undisturbed beech forests, located in the Shirakami Mountains (SM), Tsugaru Mountains (TM), and Hakkoda Mountains (HM). High quality figures are available online.

Traps were checked 24 and 48 hours after deployment each season, and all trapped dung beetles were collected. Voucher specimens were deposited at the Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, Tokyo, Japan.

Data analysis

First, to evaluate inter-sample variation in the composition of dung beetle assemblage within each trap set baited with mammalian feces at the 3 sites, the Friedman test was conducted for 10 samples, i.e., 5 sampling points × 2 terms (24 and 48 hours after deployment). Second, to evaluate the completeness of the dung beetle samples, the true species richness of each sample was estimated using the abundance-based coverage estimator (Chao and Lee 1992). This estimator uses species-bysample data and was only calculated when the total abundance captured was > 1. Furthermore, the estimator, which was a nonparametric richness estimator, assumed that the observed number of species in a sample comprised a number of abundant (common) and rare (infrequent) species. A cutoff value of 10 was used as the rare or infrequent boundary for the present study, as recommended by Chazdon et al. (1998). The software Estimates (Colwell 2006) was used to generate the abundance-based coverage estimator estimate with 100 randomizations without replacement.

Figure 2.

Representation of the multiple dimensional scaling analysis based on the Bray-Curtis similarity index for dung beetle assemblages collected in the Tsugaru Mountains (TM), Shirakami Mountains (SM), and Hakkoda Mountains (HM) during spring (circles) and summer (triangles) 2009. High quality figures are available online.

Since the sampling effort was the same at each sampling site, dung beetle species counts across sampling sites were compared using totals, percentages of occurrence, and inverse Simpson's diversity index (1/D) scores (Magurran 1988). Bonferroni z-statistics (Neu et al. 1974) was used to specify dominant species in the dung beetle assemblages collected at each location, assuming that all species appeared at the same occurrence rate. To evaluate the similarity in beetle assemblage compositions among sites, a multiple dimensional scaling analysis (Ludwig and Reynolds 1988) based on the Bray-Curtis similarity index (Bray and Curtis 1957) was used. In addition, the feces preference of each dung beetle species was evaluated using Bonferroni z-statistics. For each beetle species, it was assumed that the expected frequency of occurrence was the same for all types of mammalian feces.

Feces preference of dung beetle species

The results of our study clearly indicated that most dung beetles inhabiting undisturbed beech forests had the ecological characteristic of selecting a specific mammalian feces, as opposed to dung beetles inhabiting tropical landscapes; quite a few tropical dung beetles are considered generalists in their feeding preferences (Hanski and Cambefort 1991b). In particular, A. eccoptus, which was observed most frequently, is recognized as a specialist species that strongly prefers the feces of the Japanese macaque only. Since A. eccoptus was not observed in the TM, where the macaque population has been extinct for more than 100 years (Table 1), a reasonable conclusion is that the occurrence of A. eccoptus is highly dependent upon the availability of macaque feces.

However, during spring, the abundance of A. eccoptus was almost 3 times higher in the HM than in the SM, which is the only habitat where the macaque troops have continuously ranged (Table 4). This unexpected result might be explained as follows. First, macaque feces are available within the HM because non-troop solitary male macaques have frequented there (Oi et al. 1997; H. Enari, unpublished data; see Table 1), possibly allowing for the survival of the local population of A. eccoptus in the HM today. Second, the air temperature in the HM during spring was relatively low (because of its inland climate) compared with other 2 sites (Table 1) and could be more suitable for the outbreak of A. eccoptus in the forests. A massive outbreak of the beetle was observed in the SM at temperatures of around 10° C (Enari et al. 2011). To support these 2 explanations more empirically, further quantitative research on the minimum requirement of macaque feces for beetle reproduction would be required.

The results showing feces preference also demonstrated that few dung beetle species avoided using serow feces. This means that serow feces could be considered sharable resources for most dung beetle species, which resulted in the composition of dung beetle assemblages using serow feces differing between study sites (Figure 3). In contrast, bear and cattle feces were not attractive to most dung beetles (Table 6). In most study sites during both spring and summer, dung beetle species did not recognize cattle feces as a useable resource. This is possibly because cattle feces are not usually found in forest environments. The fundamental reasons for these fecal preferences are not fully understood from the present findings, but clearly cannot be explained by the contents of the respective mammalian feces alone. In fact, although there were no notable differences between the contents of bear and serow feces in spring or between serow and cattle feces in summer (Table 2), the beetle assemblages observed in each feces were not similar in composition. These facts most likely indicate that the digestive process of each mammal species, which potentially influences the fiber, nitrogenous, moisture, and volatile contents of feces, also affects the feces preference of dung beetles, as proposed by Davis (1989) and Davis and Scholtz (2001).

Influences of mammalian species richness on dung beetle assemblages

In the collections captured using pitfall traps, 3 families representing 14 species were observed. All of the species except 2 are classified as forest species (Kawai et al. 2005); the remaining 2 species, Aphodius uniformis Waterhouse (Coleoptera: Scarabaeidae) and Caccobius brevis Waterhouse, which showed a low frequency of occurrence in the present study, range naturally in open-land habitats (Kawai et al. 2005). As with the study of cool-temperate dung beetles by Enari et al. (2011), the present data also demonstrated that most species showed obvious seasonal prevalence and emerged in abundance only during spring. One possible explanation for the massive appearance of dung beetles in spring might be the high availability of fresh feces. Feces were cryogenically preserved under the snow during winter and appeared on the ground as the snow melted in early spring. Further research on the resource value of such preserved feces for dung beetle species would be required to support this suggestion.

It is highly likely that the beetle community structure is sensitive to existing mammalian fauna, as evidenced by the fact that the species composition of assemblages varied widely with study site in both spring and summer (Figure 2). It should be noted that the species diversity of dung beetles was not positively correlated with the number of existing mammalian species; the beetle assemblages collected in the TM, which showed the most incomplete mammalian fauna among the study sites, demonstrated the highest species richness. This finding does not support previous studies (Estrada et al. 1999; Feer and Hingrat 2005; Andresen and Laurance 2007; Nichols et al. 2009), which commonly concluded that the population loss of mammalian species results in a decline in species richness of the beetles. The present result may be explained by the presence/absence of A. eccoptus, i.e., the most frequent species, which has also been shown to have high environmental tolerance (Enari et al. 2011). In sum, it is reasonable to consider that the massive occurrence of this species reduced the apparent values of inverse Simpson's diversity index in HM and SM during spring, owing to its statistical characteristics. When the index was recalculated for the spring dataset with A. eccpotus excluded, its value was 2.8 and 3.4 in HM and SM, respectively.

From the present findings, it may be concluded that although mammalian species richness is not necessarily positively correlated with species diversity in dung beetle assemblages in cool-temperate forests, the absence of the macaque population directly results in a marked reduction of the beetle abundance, as shown by the loss of A. eccoptus, which forms a commensal relationship with macaques during spring. To provide a better understanding of this exceptional conclusion in contrast to the previous studies (Nichols et al. 2009), further empirical research on the life-history traits and population dynamics of each dung beetle species would be required.

Table 1.

Environmental conditions (°C) and present distributions of large mammalian species in each study site located in the northernmost part of mainland Japan.

Table 2.

Percentage of the contents of each mammalian feces sample^a used in the baited pitfall traps.

Table 3.

Regional and seasonal differences in the compositions of dung beetle species captured by pitfall traps baited with the feces of Japanese macaques, Asiatic black bears, Japanese serow, and cattle in primary beech forests, located in the Tsugaru Mountains (TM), Hakkoda Mountains (HM), and Shirakami Mountains (SM), northern Japan.

Table 4.

Diversity and composition of dung beetle species captured by pitfall traps baited with the feces of four large mammalian species—Japanese macaques, Asiatic black bears, Japanese serows, and cattles—in primary beech forests located in the northernmost part of mainland Japan during spring (June 2009).

Table 5.

Diversity and composition of dung beetle species captured by pitfall traps baited with the feces of four large mammalian speciess—Japanese macaques, Asiatic black bears, Japanese serows, and catties—in primary beech forests located in the northernmost part of mainland Japan during summer (August 2009).

Table 6.

Preference of dung beetles (observed at > 10 individuals) for each mammalian feces, confirmed by baited pitfall traps in primary beech forests located in the northernmost part of mainland Japan during spring (June 2009). The data on occurrence frequency was pooled from the 3 study sites.