, and their early colonization is key to maximizing this ecosystem service.


INTRODUCTION
When cattle excrete dung onto the soil surface, the failure of the pats to break down can challenge the productivity of grazing on rangelands (Fincher, 1981). When cattle consume forage, any nutrients not digested are returned to the system in the form of dung and urine (Haynes & Williams, 1993;Wu & Sun, 2010). The undigested plant material that comprises dung is deposited on the soil surface, smothering plant growth in that area (Holter, 2016;MacLusky, 1960). Pasture fouling through continuous dung deposition that fails to degrade quickly can represent a substantial problem to ranchers if left unmanaged. When a dung pat is deposited on a pasture, all of the available forage underneath and up to a 5 m radius around the pat is unused by grazing cattle until the pat is incorporated into the soil (Weeda, 1967). Dung loses 22% (but up to 80%) of its nitrogen (N) to volatilization within 60 d of deposition (Nichols et al., 2008;Weeda, 1967). Other important nutrients such as phosphorus (P) and potassium (K) are present in dung pats in much smaller quantities and can be lost to leaching and runoff when left on the soil surface (Gillard, 1967;Nichols et al., 2008;Petersen, Lucas & Woodhouse, 1956). Volatilization and reductions of these elements decreases the nutrient availability to the plant community, resulting in lower quantity and quality of forage for future cattle grazing (Aarons et al., 2009;Bang et al., 2005).
A variety of factors affect how quickly dung is incorporated into the soil. Reports of dung degradation rates vary from 50-65 d over the season (Holter, 1979), 57-78 d in late spring to 88-111 d in late summer (Lee & Wall, 2006), and up to 3 y in cattle grazing systems with high insecticide use (Anderson, Merritt & Loomis, 1984;Strong, 1992). This variability is due to factors that include weather (Holter, 1979), seasonality (Lee & Wall, 2006), insecticide use (Suarez et al., 2003), and the nutritional quality of the dung itself (Cook, Dadour & Ali, 1996). Degradation of dung pats is facilitated by arthropods that accelerate the incorporation of the dung pat organic matter into the soil, and improve soil's aeration and water holding capacity (Macqueen & Beirne, 1975). Dung often supports dozens or even hundreds of arthropod species (Blume, 1985;Merritt & Anderson, 1977;Valiela, 1969).
Arthropods that colonize dung pats can be categorized into different functional guilds that each contribute to the eventual incorporation of the dung into the soil. One of the first studies that considered dung community function was Mohr (1943), which prompted other studies that documented arthropod succession in a dung pat and their varying niches within the micro-habitat (Cervenka & Moon, 1991;Koskela & Hanski, 1977;Sanders & Dobson, 1966). These studies are accompanied by more recent explorations of the importance of dung beetles (Scarabaeidae) and the multiple ecosystem services that they provide (Beynon et al., 2012;Manning et al., 2016;Nichols et al., 2008). One of these ecosystem services is dung beetles' ability to increase the productivity of rangeland ecosystems (Bang et al., 2005;Penttila et al., 2013). Increased rangeland productivity is achieved by bioturbation and burial of dung that results in capturing ephemeral nutrients for surrounding forage plants up to 12.7 cm away from the dung pat (Bornemissza, 1970;Macqueen & Beirne, 1975;Yamada et al., 2007). A second important ecosystem service is the suppression of dung inhabiting pests to grazing cattle (Fincher, 1981). By removing nutritional resources and habitat, dung beetles reduce pest maggot abundance (Doube, 1990;Nichols et al., 2008). Suppressing these pests is accelerated when natural enemies such as predatory staphylinid or hister beetles and parasitoid wasps colonize the dung pat (Cervenka & Moon, 1991). These ecosystem services provided by dung beetles (as well as other members of the dung arthropod community) have an economic value to the ranching operation (Beynon, Wainwright & Christie, 2015), but most of the numbers used to generate these values are at least 37 years old (Beynon et al., 2012;Fincher, 1981;Losey & Vaughan, 2006).
The goal of our study was to document the dung insect community in eastern South Dakota, and determine dung degradation rates over time in the presence and absence of this community. Cages like those employed here help to isolate the contribution of the majority of the arthropod community to dung pat degradation (Lee & Wall, 2006;Tixier, Lumaret & Sullivan, 2015). Here, we pair cages with a comprehensive description of invertebrate communities within the dung both early and late in the summer to understand how elements of this community affect degradation over the season. There are 9.12 million ha of rangeland in South Dakota (USDA-NASS), and this region represents an important transition zone between the mid and tall-grass prairie biomes (NASS, 2016). Dung-inhabiting Coleoptera from South Dakota were described nearly 50 years ago (Kessler & Balsbaugh, 1972;McDaniel, Boddicker & Balsbaugh, 1971), but these studies did not correlate these insects to dung pat degradation, and land use patterns have changed dramatically toward annual cropland over this period of time (Johnston, 2014;Wright & Wimberly, 2012). Identifying the impact of the dung arthropod community on degradation will provide ranchers a greater understanding of the benefits of conserving this poorly understood community. We hypothesize that caging pats will reduce insect colonization of the dung and impede pat degradation rates.

Study site
This study was conducted on a ranch in eastern South Dakota, US, at 44.758, −96.538 in the summer of 2016. The study site was at an altitude of 559 m in an area with an average annual rainfall of 684 mm and an average summer temperature of 19.8 • C. The 130 ha pasture was composed of mixed grasses; consisting mostly of Schizachyrium scoparium (little bluestem), Andropogon gerardii (big bluestem) and Spartina pectinata (prairie cordgrass) with predominantly silty clay and silty clay loam soil types (USDA-NRCS, 2016). The grazing season prior to and during the experiment had a 130-steer herd made up of Angus, Belted Galloway, and Irish Black breeds, that was moved among small 0.41-1.21 ha paddocks approximately every 24 h. Cattle were excluded from the experimental site during the observation periods. No insecticide or nematicide treatments had been used on cattle on this ranching operation in more than 10 y.

Dung degradation measurements
Dung (<2 h old; 90 kg collected twice) was collected from the pasture on 04/06/2016 and 05/06/2016 before 10:00. Fresh dung pats were homogenized and stored in bags at −25 • C for 72 h to ensure all arthropods had been killed. Dung was removed from the freezer, completely thawed, and homogenized prior to use in the experiment. Aliquots of the dung (1,000 ± 10 g) were weighed, individually bagged, and stored for 24 h before placing them in the field. Each bag of weighed dung became a ''sentinel pat'' to represent a dung pat deposited by grazing cattle. Observation sites (n = 84) were placed in the pasture so sites were at least 5 m apart. At each site, a sentinel pat was placed on top of mesh with 2.5 cm square holes to allow for ease of pat removal. Each site was randomly assigned to one of three treatments. In the first treatment (inclusion; n = 36), dung pats were left completely exposed with no covering. In the second treatment (exclusion; n = 36), the pats were surrounded by a PVC cylinder (25 cm diam., 25 cm tall), buried at least 12 cm into the ground to reduce ground colonization of the pat. The tops of these cylinders were covered in fine mesh screen (<1 mm opening) and secured with a plastic tie. The final control treatment (sham cage; n = 12) used the same cylinder design as the exclusion treatment, but with three 10 × 10 cm holes cut on the sides to allow arthropods to travel into the cylinder. A wire top was used to cover these sham cylinders that had 3 cm openings. This third treatment was added to test whether the exclusion cage had direct effects on dung degradation rates.
To determine degradation rates, pats from the three treatments were weighed over time. The entire experiment was repeated twice over the season, once beginning on 10-June and once on 28-July. Randomly selected pats (Inclusion [six pats], Exclusion cage [six], and Sham cage [two] on each time point) were removed 2, 4, 7, 14, 28, and