Niche, PREFERENCE OF A

Rice, Marlin E., 2010, Niche Preference of a Coprophagous Scarab Beetle (Coleoptera: Scarabaeidae) for Summer Moose Dung in Denali National Park, Alaska, The Coleopterists Bulletin 64 (2), pp. 148-150 : 148-149

NICHE PREFERENCE OF A COPROPHAGOUS SCARAB BEETLE ( COLEOPTERA : SCARABAEIDAE ) FOR SUMMER MOOSE DUNG IN DENALI NATIONAL PARK, ALASKA

Some of the smallest scarab beetles in the world, measuring no more than 2–8 mm in length, are in the genus Aphodius Illiger (sensu lato) (tribe Aphodiini ). They feed on vertebrate dung or detritus and are the dominant coprophagous beetles in northern Europe ( Hanski 1991). The life history of a few species is well documented, but for many species very little or nothing is known (Gordon and Skelley 2007; Ratcliffe and Paulsen 2008), including their larval host preferences.

Moose, Alces alces (L.), are the largest cervids in the world with males weighing 300–725 kg ( Reid 2006; Van Ballenberghe 2006). Moose are possibly the most abundant herbivore in Denali National Park, Alaska, with an estimated population of 2,000 –2,500 individuals ( Meier 2009), and they occur throughout the interior boreal lowlands, or taiga, ecological zone ( Hooge et al. 2006). Only caribou, Rangifer tarandus (L.), match the population density of moose within Denali National Park ( Meier 2009). During the summer months, the daily moose output of dung ranges from 1.1–2.2 kg dry weight per animal per day in Michigan and Ontario populations ( Persson et al. 2000). Because of their body size and population density within Denali National Park, moose could be expected to produce substantial quantities of dung within the taiga ecosystem, which could serve as a valuable food source for coprophagous insects.

Moose dung deposited in the summer, when many coprophagous insects would be active, is distinctly different from moose dung deposited in the winter (Murie and Elbroch 2005). Winter dung consists of large numbers (78–192) of loose, elongate or round, and usually smooth pellets up to 45 mm long. In contrast, summer dung is a conglomerate of thickly and tightly packed pellets or droppings that are soft and almost formless, somewhat resembling domestic cow dung. The inner core of summer moose dung remains green and wet, but the exterior quickly becomes hard and dry. Differences in dung consistency are directly related to moose diet (Murie and Elbroch 2005). Moose browse on dry twigs during the winter and the dung consists of small bark and wood fragments. In the summer, moose browse on succulent green plants. In spring and fall, with the shift to and from a succulent diet, the dung is intermediate in shape and may retain the pellet form, but may be distorted and cling in a mass. Caribou, which are smaller (65–300 kg) than most moose ( Reid 2006), produce smaller dung pellets (<16 mm) than moose dung pellets, while the summer dung consists of coalesced pellets, similar to sheep dung (Murie and Elbroch 2005).

During 7–9 August 2009, the taiga at Savage River Campground (63°42′57″N, 149°15′46″W), Denali National Park was searched for animal dung and the associated insect fauna. Dense stands of white spruce, Picea glauca (Moench) , black spruce, Picea mariana (Mill.) , and interspersed open areas covered with grasses and low growing, woody shrubs were searched for animal dung by following established animal trails. Of the two major herbivore species (moose and caribou) in Denali National Park, only moose dung was found at this location. Dung was categorized as either summer moose dung ( Fig. 1) or winter moose dung ( Fig. 2 ). Summer moose dung was examined for insects by manually breaking the dung and cutting it with a knife into small pieces over a sheet of white paper. The observed coprophagous scarab larvae, pupae, or adults were then counted. When winter moose dung pellets were found, only those that appeared to be relatively fresh and deposited during the previous winter or spring were examined. Fifty of the largest pellets from each pile were inspected for external indications of insect egress, broken into two pieces, and examined for either insects or their tunneling activity. An equal number (n = 13) of winter moose dung piles and summer moose dung pats were sampled. All dung was examined in situ except for three pats of summer moose dung, which were transported and held indoors to allow for adult emergence. Adults emerged from these pats on 18–23 August 2009.

Winter moose dung contained no evidence of insects or their activity. The winter dung was heavily compacted with twig and bark fragments, and resembled course, compressed sawdust. Low levels of moisture were present in the dung, but these likely came from recent rains as opposed to originating from the defecating moose. It is unlikely that winter dung would retain moisture levels necessary for coprophagous larval development because of the relatively small mass per pellet.

Summer moose dung often contained larvae, pupae, or adults of coprophagous scarabs, and had noticeably higher moisture content with an inner core that was frequently soft or semi-firm when compared to winter moose dung. Collected adults were identified as Aphodius (Planolinoides) borealis Gyllenhal and 10 of 13 (76.9%) summer moose dung pats contained this species. Two dung pats had high insect densities of 55 and 151 larvae, pupae, or adults, but these densities were the exceptions. The range of A. borealis in all other moose dung pats was at much smaller densities of 0–11 insects. The mean density of A. borealis larvae, pupae, or adults per summer moose dung pat in Denali National Park during August was 18.3±11.8 SE.

Aphodius (Planolinoides) borealis is a Holarctic species that occurs in North America, primarily in boreal forests during April through November and may be uncommon in some environments ( Gordon 1983; Bosquet 1991; Gordon and Skelley 2007). Adults are 4.0– 5.9 mm in length with black elytra and small red areas on the humerus and apical declivity, and male heads are trituberculate (Gordon and Skelley 2007). The species is very rare in mountainous northern Spain and ranked 13 out of 19 species in abundance, comprising only 0.24% of the Aphodius population (Menéndez and Gutiérrez 1996). Gordon (1983) stated that A. borealis may use deer dung, but probably also occurs in dung of moose, caribou, and possibly ground squirrel pellets. Later, Gordon and Skelley (2007) stated that no specific data were available with the exception of specimens labeled “moose dung” and “in rainbow trout stomach”. Hanski and Kuusela (1983) reported that A. borealis in Finland uses European elk (i.e., moose) dung on the Åland archipelago but did not define the type or structure of moose dung used by the beetle.

The significance of the observations in Denali National Park is that A. borealis clearly has a niche preference for larval development in the microhabitat and host quality that exists in summer moose dung. Because many adult Aphodius (sensu lato) are fluid feeders, while the larvae feed on wet solid material (Gittings and Giller 1997), the higher moisture retention, greater mass, and possibly better nutritional content are partial explanations why summer moose dung is a preferred host for this coprophagous scarab beetle. The absence of any feeding or insect life stage suggests that A. borealis does not use the drier, smaller, and courser winter moose dung pellets as either a larval or adult host.

Thanks to National Park Service staff Robb Hannawacker, Jane Lakeman, and Lucy Tyrrell for assistance and courtesies extended during this study at Denali National Park. Thanks also to Brett Ratcliffe for providing the identification of A. borealis . This research was conducted under the authority of the National Park Service, Study 802, Park Code Permit # DENA 862. Voucher specimens are deposited in the insect research collections at Denali National Park , Alaska, Texas A&M University, and University of Nebraska —Lincoln .

Figures

Fig. 2. Winter moose dung, Denali National Park, Alaska. Coin is 24.3 mm wide.