Dung Decomposition Research Articles

Complementarity of dung beetle species with different functional behaviours influence dung–soil carbon cycling

Decomposition of large ungulate herbivore dung and its subsequent incorporation into the soil play key roles in carbon and nutrient cycling and are important for grassland productivity. Dung beetles contribute to the initial breakdown and transport of organic matter from the dung into the soil but how they interact with the microbial community to modify decomposition processes remains poorly understood.Using a mesocosm experiment, we investigated the individual and interactive effect of two dung beetle species with contrasting functional behaviour (dweller species: Agrilinus ater (De Geer 1774) vs. tunneler species: Typhaeus typhoeus (Linneaus 1758)) on dung C cycling (CO2 fluxes and C transfer through the soil profile) and resultant effects on microbial activity and biomass in the soil.Both dung beetle species contributed significantly to dung removal, reducing the C lost through microbial respiration from the whole mesocosm. However, C concentrations measured in leachates from the mesocosm were only significantly higher in the presence of the tunneler species, indicating that tunnelling activity was required to increase C transfer down the soil profile. The combined effect of the two dung beetle species resulted in the highest soil microbial respiration from the soil and in particular in the 2–10 cm depth increment, suggesting positive complementarity effects between species with different functional behaviour.We conclude that the return of C in the form of dung in grasslands, coupled with the activity of a functionally diverse dung beetle assemblage, could result in short term fluctuations in soil microbial activity with important consequences for soil C cycling.

Disentangling the ‘brown world’ faecal–detritus interaction web: dung beetle effects on soil microbial properties

Many ecosystem services are sustained by the combined action of microscopic and macroscopic organisms, and shaped by interactions between the two. However, studies tend to focus on only one of these two components. We combined the two by investigating the impact of macrofauna on microbial community composition and functioning in the context of a major ecosystem process: the decomposition of dung. We compared bacterial communities of pasture soil and experimental dung pats inhabited by one (Aphodius), two (Aphodius and Geotrupes), or no dung beetle genera. Overall, we found distinct microbial communities in soil and dung samples, and that the communities converged over the course of the experiment. Characterising the soil microbial communities underlying the dung pats revealed a significant interactive effect between the microflora and macrofauna, where the diversity and composition of microbial communities was significantly affected by the presence or absence of dung beetles. The specific identity of the beetles had no detectable impact, but the microbial evenness was lower in the presence of both Aphodius and Geotrupes than in the presence of Aphodius alone. Differences in microbial community composition were associated with differences in substrate usage as measured by Ecoplates. Moreover, microbial communities with similar compositions showed more similar substrate usage. Our study suggests that the presence of macrofauna (dung beetles) will modify the microflora (bacteria) of both dung pats and pasture soil, including community diversity and functioning. In particular, the presence of dung beetles promotes the transfer of bacteria across the soil–dung interface, resulting in increased similarity in community structure and functioning. The results demonstrate that to understand how microbes contribute to the ecosystem process of dung decomposition, there is a need to understand their interactions with larger co‐occurring fauna.

Carbon and nitrogen cycling in an integrated soybean-beef cattle production system under different grazing intensities

Abstract:The objective of this work was to evaluate the effect of grazing intensity on the decomposition of cover crop pasture, dung, and soybean residues, as well as the C and N release rates from these residues in a long-term integrated soybean-beef cattle system under no-tillage. The experiment was initiated in 2001, with soybean cultivated in summer and black oat + Italian ryegrass in winter. The treatments consisted of four sward heights (10, 20, 30, and 40 cm), plus an ungrazed area, as the control. In 2009-2011, residues from pasture, dung, and soybean stems and leaves were placed in nylon-mesh litter bags and allowed to decompose for up to 258 days. With increasing grazing intensity, residual dry matter of the pasture decreased and that of dung increased. Pasture and dung lignin concentrations and C release rates were lower with moderate grazing intensity. C and N release rates from soybean residues are not affected by grazing intensity. The moderate grazing intensity produces higher quality residues, both for pasture and dung. Total C and N release is influenced by the greater residual dry matter produced when pastures were either lightly grazed or ungrazed.

Invasive Cane Toads’ Predatory Impact on Dung Beetles is Mediated by Reservoir Type at Artificial Water Points

Disruption to ecosystem functioning associated with biological invasions can have dramatic effects on the production and biodiversity values of ecosystems. In semi-arid rangelands of Australia, invasive cane toads (Rhinella marina) prey on dung beetles that were themselves introduced to promote nutrient cycling and reduce parasite burdens of livestock. Cane toads’ colonization of rangelands has been facilitated by artificial water points (AWP) which provide cattle with drinking water. Most AWP in northern Australia comprise bores that pump water into earthen reservoirs (dams). Dams typically support large toad populations because they allow toads’ access to water without which they could not survive. Here, we ask if restricting toads’ access to water at AWP can reduce toad populations, toads’ predatory impact on dung beetles, and the rate of dung decomposition by dung beetles. We contrasted toad and dung beetle populations, toad diets, and dung removal rates at AWP fitted with dams or tanks as reservoirs. In comparison to dams, tanks provide toads with little access to water. Population densities of toads were five times higher at dams than tanks. Conversely, population densities of dung beetles were 12 times lower at dams than tanks. Mass loss of experimental dung pats after 2 days was 13% greater at tanks than dams. Our study provides evidence that consumption of detritivores by an introduced predator can retard dung decomposition in a rangeland ecosystem. Restricting toads’ access to water at AWP should benefit livestock production by reducing both toad populations and toads’ predatory impact on dung beetles.

Effects of the Activity of Coprophagous Insects on Greenhouse Gas Emissions from Cattle Dung Pats and Changes in Amounts of Nitrogen, Carbon, and Energy.

Effects of coprophagous insects on greenhouse gas emissions from cattle dung pats were investigated during the initial stage in the decomposition of dung, with accompanying changes in nitrogen, carbon, and energy content. We set up three treatments with adults of Caccobius jessoensis Harold (dung beetle) and larvae of the fly Neomyia cornicina (F.): 1) dung with dung beetles; 2) dung with fly larvae; and 3) dung without insects. In these treatments, the gas flux was measured from air flow exiting the glass containers connected with an in vitro continuous gas analysis system. Total gas fluxes from dung pats with fly larvae were lowest in carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). The presence of dung beetles significantly increased CO2 flux from dung, but reduced CH4 flux compared with dung without insects. Fluxes of N2O from dung pats with dung beetles and without insects had distinct peaks at different times after the start of the experiment, while N2O from dung with fly larvae was emitted in extremely low levels throughout the experiment. Carbon (C) content in dung with beetles was significantly lower than that of untreated dung pats designated as fresh dung, whereas that of dung with fly larvae was higher than dung with beetles and without insects. Nitrogen (N) content was significantly lower in dung with fly larvae than the other treatments. Contents of C and N in fly pupae were 35.87 and 8.05%, respectively. During the larval growth of the fly, energy accumulated in the fly body was 2,830 J/g.

Deposition and decomposition of cattle dung and its impact on soil properties and plant growth in a cool‐temperate pasture

AbstractLivestock dung provides an important direct pathway by which carbon and nutrients enter soils in pasture ecosystems and affects carbon and nitrogen cycling indirectly through changes in soil and plant properties. Here, we quantify dung deposition, decomposition, and the effects of dung on soil and plants in a Zoysia japonica grassland in Japan. We determined (1) the distribution of dung, (2) the mass loss rate of dung and the amount of carbon respired as CO2, and (3) changes in soil properties and aboveground biomass of Z. japonica. Dung deposition was 4.0–9.7 g C and 0.4–1.0 g N m−2 year−1 and distributed patchily (Morishita's Iδ > 1). Most (71 %) of the carbon in dung deposited in June was lost within a single grazing period by aerobic decomposition, more than mass loss rate of Z. japonica litter in the first year (about 50 %), suggesting that grazing and defecation can accelerate carbon cycling compared with the typical litterfall–decomposition regime. Nitrogen in dung mass entered the soil as ammonium nitrogen and was nitrified. The spatiotemporal distribution of these processes corresponded to that of stimulated Z. japonica growth. These results suggested that dung deposition significantly affected the inorganic nitrogen status of soil and, therefore, the growth of Z. japonica. However, these effects were very restricted temporally (July–August) and spatially (within 10 cm from dung edge). Thus, such spatiotemporally restricted effects combined with the patchy distribution of dung may contribute to the heterogeneous structure of pasture ecosystems.

Interactions between C : N : P stoichiometry and soil macrofauna control dung decomposition of savanna herbivores

Summary Although dung of mammalian herbivores is an important pathway for nutrient return in savanna ecosystems, differences in dung decomposition rates among species have been little studied. We measured the rates of dung deposition and decomposition for various herbivores in a moist Tanzanian savanna and the related differences among species to nutrient concentrations and the activities of soil macrofauna (e.g. different mesh sizes of decomposition bags, or presence and absence of dung beetles). Dung C : N : P stoichiometry varied widely among species, which could in part be explained by differences in feeding strategy (browsers vs. grazers) and digestive physiology (ruminants vs. non‐ruminants). Rates of both decomposition and nutrient release were influenced by the C : N : P stoichiometry of dung, with lower relative losses of the least abundant nutrient in the dung. Surprisingly, soil macrofauna increased the relative losses of the least abundant nutrient, thereby stabilizing the ratio of N loss to P loss. Dung beetles increased rates of N and P release from wildebeest dung significantly and also increased N availability in the soil. We conclude that rates of nutrient return in dung depend not only on where herbivores deposit their dung, but also on its C : N : P stoichiometry, the activity of soil macrofauna and interactions between these factors. These factors may therefore influence the relative availabilities of N and P in the soil and hence the functioning of savanna ecosystems.

Decomposition of cattle dung on mixed grass-legume pastures

Animal excreta contribute positively to nutrient cycling and can improve the quality of soil (Dubeux Jr. et al. 2009; Carvalho et al. 2010). Cattle excrement, when evenly distributed over a pasture, can help to maintain plant nutrition without the application of fertilizers. The introduction of legumes intercropped with grasses benefits the soil by means of nitrogen fixation. When ruminant animals eat legumes, the feces produced may have lower C:N, C:P, lignin:N and lignin:P ratios, promoting better nutrient return to the soil than when cattle eat only grass. Given the importance of nutrient return from and decomposition time of cattle feces on pastures, the objective of this study was to quantify the decomposition of feces of heifers managed in mixed grassshrubby legume pastures and grass-only pastures.

Decomposition of cattle feces from Pennisetum purpureum pastures managed under different post-grazing stubble heights

Pasture management can affect cattle diets. Post-grazing stubble height is a structural characteristic intrinsically linked to forage quantity and quality. Stubble height also indicates forage utilization rate, and as a result, affects nutrient return pathways (excreta or litter) and, ultimately, nutrient cycling. While deposition of cattle excreta affects soil chemical and physical characteristics (Carran and Theobald 2000), slow release of nutrients from cattle dung delays nutrient bioavailability for subsequent forage growth (Haynes and Williams 1993). This study evaluated how different post-grazing stubble heights on elephant grass (Pennisetum purpureum) pastures may affect cattle dung decomposition and nutrient release.

Using citizen scientists to measure an ecosystem service nationwide

The decomposition of dung constitutes an ecosystem service of massive proportions. Previous studies addressing how it depends on individual invertebrate taxa have been focused on small spatial scales, neglecting the impact of large-scale factors like climate. Here, we use the concept of "citizen science" to quantify taxon-specific contributions to dung decomposition at the level of a nation. Young people across Finland manipulated the decomposer communities of cow pats, then measured changes in pat mass over the grazing season. In southern Finland most (90%) of the cattle dung hitting pastures decomposed in just two months, whereas 1100 km to the north the corresponding fraction was smaller (74%). Of the total invertebrate-caused decomposition (13% of dung pat mass, independent of latitude), large tunneling dor beetles in the genus Geotrupes account for 61%, hence removing dung twice as fast as do smaller dung-dwelling beetles and earthworms. Overall, this paper illustrates how ecologists may direct citizen scientists to implement massive ecological experiments. Compared to an approach based purely on professional scientists, we saved three-quarters of the costs. Ultimately, citizen science may offer a key tool for testing current ecological theories at relevant spatial scales--and for disseminating these theories in the process.

Effects of yak dung patch dropped in cold season on soil and pasture on the Qinghai-Tibetan Plateau

To clarify how dung patches from grazing yaks affect soil and pasture in the alpine meadow of Qinghai-Tibetan Plateau, yak dung was collected, mixed and redistributed in a cold grazing season. The soil physical and chemical properties and forage growth were then monitored under the yak dung patch, and 10cm and 50cm from the edge of yak dung patches. The result has shown that yak dung significantly improved soil moisture, total organic matter, and soil available N and P under or close to the dung patches. The forage production at 10cm from the dung patch (303g/m2) was significantly higher than that at 50cm from the dung patch (control) (284g/m2) in the second year, while the production was similar to the control in the first and the third year. The process of yak dung decomposition was slow and yak dung remains were observed 3years after the drop. The dung patches also formed a strong ‘shell’, very difficult for plant underneath to penetrate and grow. Therefore, almost all plants under yak dung patches died, leading to decline in forage yield in the first, second, and the third year. In practice in the Qinghai-Tibetan Plateau regions, yak dung is often collected as fuel by the local farmers. Removing yak dung from alpine meadow may on one hand lead to losses in soil nutrients, but on the other hand reduces some of the negative effects, e.g. the reduction of forage yield under yak dung patches.

Endozoochory by European bison influences the build-up of the soil seed bank in subcontinental coniferous forest

The faeces of large herbivores include viable seeds of many plant species. With dung decomposition, some seeds migrate into the soil and influence seed bank build-up. However, only a few papers report evidence of this process, and only from grasslands. In forest studies, this subject has so far been neglected. Therefore, I ask in this paper whether seeds present in the dung of European bison migrate to the forest soil seed bank and influence its build-up. I sampled soil from underneath European bison dung pats and from surrounding areas (control samples). Samples were divided into shallow (0–5 cm) and deep (5–10 cm) series. Soil seed bank content was studied in the greenhouse for 2 years. The shallow seed bank under dung pats was characterized by the highest species richness (49 species) and seed density (>2,000 m−2). Urtica dioica, Juncus effusus and Carex remota showed a demonstrable increase in seed density in the shallow seed bank underneath dung. Three years after dung deposition, seeds of endozoochoric origin influenced the soil seed bank of coniferous forest. U. dioica, J. effusus, C. remota and other species of deciduous forests and grasslands (Agrostis capillaris, Milium effusum, Polygonum hydropiper, Polygonum mite, Scrophularia nodosa, Stachys sylvatica, Veronica chamaedrys) caused an increase in seed density (by 61 %) and species richness (by 33 %) of the shallow soil seed bank underneath dung in comparison with the control soil seed bank.

Species‐rich dung beetle communities buffer ecosystem services in perturbed agro‐ecosystems

SummaryMany studies document high levels of functional redundancy in ecosystems, suggesting that species extinctions will not be detrimental to ecosystem functions and services. However, apparently redundant taxa may prove critical for sustaining ecosystem functions and services in the context of environmental perturbations.Dung beetles (Coleoptera:Scarabaeidae) provide a valuable ecosystem service in temperate agro‐ecosystems by increasing rates of dung decomposition and nutrient cycling. However, there is concern that these services may be negatively affected by changes in species richness and composition due to changes in pasture management and negative effects of anthelmintics used to control livestock parasites.We used a mesocosm experiment to investigate the functional importance of dung beetle species richness in a system perturbed by the anthelmintic, ivermectin. We varied dung beetle species richness within three functional groups in factorial combination with ivermectin treatment.In the short term (1–4 weeks), multi‐species dung beetle assemblages achieved higher decomposition rates than monocultures, but only in ivermectin‐treated dung. Varying species‐specific sensitivities to ivermectin meant that species‐rich assemblages sustained ecosystem functioning in the context of this anthropogenic perturbation.Over the longer term (36 weeks), there was a significant, positive effect of species richness on dung decomposition in both ivermectin‐treated and untreated dung, underlining the functional importance of maintaining a species‐rich dung processing community even in the absence of perturbations to the system.Synthesis and applications. The interacting effects of dung beetle species richness and ivermectin highlight the importance of maintaining diverse assemblages in the face of anthropogenic perturbations and suggest that apparent functional redundancy of species in agro‐ecosystems should be interpreted cautiously. Furthermore, different farm management practices (e.g. pesticide use and fragmentation of habitats) may have consequences for ecosystem functions and services that exceed the effects of each when considered in isolation.

Consequences of alternative and conventional endoparasite control in cattle for dung-associated invertebrates and ecosystem functioning

Invertebrates associated with livestock dung provide a valuable ecosystem service of dung decomposition, but can be affected negatively by the use of livestock parasite-control products (anthelmintics). Alternative products are promoted as environmentally sustainable, but effects on dung fauna and dung processing have not yet been investigated. We assessed the effects of one conventional product (ivermectin) and three alternatives (a homoeopathic product, Bug A Tub (a free-choice lick containing <5% diatomaceous earth, plant oils and nutritional supplements) and a copper bolus), on dung fauna and decomposition. Bug A Tub reduced the attractiveness of dung, the abundance of dung-associated insects in the soil beneath pats, emergent insect biomass and dung beetle (Coleoptera: Scarabaeidae) emergence. Ivermectin dramatically altered insect assemblages, reducing emergent fly biomass. Ivermectin also reduced emergent dung beetle abundance. Dung from ivermectin-treated cattle had a significantly lower rate of decomposition, similar to when invertebrates were excluded, but none of the alternative products affected decomposition. Insect emergence varied widely for dung collected from cattle grazing different fields, highlighting the need to ensure experimental products are not confounded with dung source. Dung from ivermectin-treated cattle can act as an ecological trap (a poor-quality environment which associated invertebrates are forced to colonise) with potentially major consequences for the ecosystem service of dung decomposition. Bug A Tub can affect insects colonising dung, highlighting a need for tests on the environmental safety of alternative products; such testing is not currently a legal requirement.

Herbage Quality and Animal Performance in a Coconut Cattle Inte grated System

The effect of controlled grazing on the natural herbage growing in coconut plantation on the performance of cross-bred heifers as well as on herbage yield, botanical composition and the quality were examined in an experiment for one year duration in a coconut estate at Kotawila, Kamburugamuwa. There were four treatments namely coconut without fertilizer (T1); coconut with fertilizer (CRI recommended levels) (T2); heifers grazed natural herbage (T3); and heifers grazed natural herbage with tree fodder (2 kg/d) and concentrate supplement (250 g/d) (T4). The experiment design was a RCBD with 3 replicates and the stocking rate was 2 heifers/ 0.4 ha. The daily weight gain (19.60 g/head/d) and body condition (-0.07) were poor when no feed supplements were given. Provision of tree fodder and concentrate (Gava thriposha) greatly improved the daily weight gain (28.23 g/ head/d) and body condition (0.09) of heifers. It was also observed that the season had an influence on growth and body condition.Herbage yield was higher in T2 as compared to T1 due to non grazing and fertilizer application. When compared the two treatments with animals, herbage yield of T4 were higher due to low grazing pressure imposed by supplementation. The N percentage of herbage also showed a similar trend. Over grazing without supplements (T3) would have depleted the soil and herbage N, and thereby conservation of N through recirculation within the animal. The dry period would have aggravated this condition by reducing the dung decomposition rate and increasing the urine evaporation rate. Grazing also improved the botanical composition of herbage. T3 and T4 treatments contained 55.35, 18.84 and 25.82% of grasses, legumes and other species, respectively. Herbage of T1 and T2 contained 18.5, 22.54 and 58.96% of grasses, legumes and other species, respectively. Axonopus affinus, A. compressus and Puraria phaseoloides like prostate species were dominant in T3 and T4 while Ocimum tenuiflorum and Urena lobota and Eupatorium odoratum like upland erect weed species were dominant in T1 and T2.The results show that the integrated management system based on coconut and cattle, could achieve sustain able improvements on stock performance, even within a short period of time. Actual benefits should be investi gated in the long term.

Generalist dung attraction response in a New Zealand dung beetle that evolved with an absence of mammalian herbivores

1. Dung beetles (Scarabaeidae: Scarabaeinae) are integral parts of many ecosystems because of their role in decomposition of dung; particularly mammal dung, which forms the diet of both larvae and adults.2. New Zealand dung beetles are unusual as they are flightless and evolved on islands with a highly depauperate mammal fauna and thus without the usual dung resource used by dung beetles elsewhere. The diet of New Zealand dung beetles is unknown.3. We hypothesised (1) that the endemic dung beetle Saphobius edwardsi would be attracted to a broad range of food types, and (2) that S. edwardsi would be able to survive and reproduce on a range of dung types and puriri (Vitex lucens) humus.4. Laboratory choice tests identified that S. edwardsi was attracted to a range of mammal, bird, invertebrate, and reptile dung types, but not to non‐dung food sources. Five‐month no‐choice tests found that beetle survival rates were lower for beetles fed with humus compared with those fed on mammal, bird, or invertebrate dung. None of the beetles reproduced.5. This study suggests S. edwardsi have a strong preference for dung, and are likely to be broad dung generalists in their feeding behaviour.

The Effect of Decreasing Temperature on Arthropod Diversity and Abundance in Horse Dung Decomposition Communities of Southeastern Massachusetts

Dung from large mammalian herbivores provides a concentrated food resource, rich in bacteria, nitrogen, and many forms of carbon that support a diverse community of arthropods. Detrital communities, while essential to nutrient cycling, are poorly studied. From July 2010 to October 2010, we sampled these arthropod assemblages using pitfall traps baited with horse dung at five sites southeast of Boston, MA. A total of 396 samples were collected, resulting in 10,299 arthropod specimens. We found a highly diverse group of arthropods dominated by Coleoptera (n=3696) and Diptera (n=3791) and noted the absence of hymenopterans, a group that was dominant in previous studies on these communities. The community had a high level of evenness (0.93 Shannon evenness) and lacked a dominant species, with no one species obtaining more than 7% relative abundance. Species accumulation curves indicate near maximum diversity was reached for each site and the study as a whole (93% maximum calculated Shannon Diversity). A strong effect of seasonality was also observed on the community, as shown by a strong shift in community at the end of August. The community sampled displayed a high similarity to previous studies, indicating a cosmopolitan distribution as well as an opportunistic community.

Area‐wide impact of macrocyclic lactone parasiticides in cattle dung

Following the treatment of cattle with veterinary parasiticides and insecticides, residues are excreted into the dung in concentrations that may be toxic to functionally important dung-colonizing insects. In the dung, these residues cause a range of well-studied lethal and sub-lethal effects, the magnitudes of which vary with the compound used, mode of administration and concentration, and the insect species in question. Particular concern has been associated with the use of macrocyclic lactones in this context. Loss of insect colonizers may delay pat decomposition, but field studies report contrasting results that reflect confounding factors such as weather conditions, pat moisture content, pat location, time of year and dung insect species phenologies. The question of fundamental concern is whether the impacts seen in experimental or laboratory studies are likely to have a functional impact on insect populations, community interactions and the economically important process of dung decomposition. Recent studies which have attempted to address these wider, landscape-level impacts in temperate ecosystems are reviewed here. These show that the extent to which chemical residues may have any sustained ecological impact will depend on both a range of farm management factors, such as the temporal and spatial patterns of chemical use, the number of animals treated and the choice of active ingredient, and a range of insect-related factors, such as abundance, population dynamics and dispersal rates. However, they also demonstrate that considerable uncertainty remains about the likely extent of such effects and that current data are insufficient to support firm conclusions regarding sustained pasture-level effects. More large-scale, longterm field experiments are required, particularly in relation to insect dispersal and functional interactions within the dung insect community.

A brown-world cascade in the dung decomposer food web of an alpine meadow: effects of predator interactions and warming

Top-down control has been extensively documented in food webs based on living plants, where predator limitation of herbivores can cascade to facilitate plant growth (the green-world hypothesis), particularly in grasslands and aquatic systems. Yet the ecosystem role of predators in detrital food webs is less explored, as is the potential effect of climate warming on detritus-based communities. We here show that predators have a brown-world role in decomposer communities via a cascading top-down control on plant growth, based on the results of an experiment that factorially manipulated presence and size of two predator species as well as temperature (warmed vs. unwarmed). The inclusion of predatory beetles significantly decreased abundance of coprophagous beetles and thus the rate of dung decomposition and productivity of plants growing surrounding the dung. Moreover, the magnitude of these decreases differed between predator species and, for dung loss, was temperature dependent. At ambient temperature, the larger predators tended to more strongly influence the dung loss rate than did the smaller predators; when both predators were present, the dung loss rate was higher relative to the treatments with the smaller predators but comparable to those with the larger ones, suggesting an antagonistic effect of predator interaction. However, warming substantially reduced dung decomposition rates and eliminated the effects of predation on dung decomposition. Although warming substantially decreased dung loss rates, warming only modestly reduced primary productivity. Consistent with these results, a second experiment exploring the influence of the two predator species and warming on dung loss over time revealed that predatory beetles significantly decreased the abundance of coprophagous beetles, which was positively correlated with dung loss rates. Moreover, experimental warming decreased the water content of dung and hence the survival of coprophagous beetles. These results confirm that the brown-world effect of predator beetles was due to cascading top-down control through coprophagous beetles to nutrient cycling and primary productivity. Our results also highlight potentially counterintuitive effects of climate warming. For example, global warming might significantly decrease animal-mediated decomposition of organic matter and recycling of nutrients in a future warmed world.

A new model for dung decomposition and phosphorus transformations and loss in runoff

Non point-source pollution of fresh waters by agricultural phosphorus (P) can accelerate eutrophication of surface waters and limit their use for drinking, recreation, and industry. An important pathway of agricultural P transport is surface runoff, to which unincorporated dung from grazing cattle can be a significant contributor. Computer models commonly used to identify agricultural areas with a high potential for P export do not adequately simulate dung application to the soil surface, dung disappearance, and dung P loss to runoff. We developed a new model to simulate these processes for grazing cattle dung. The model simulates dung organic matter decomposition and assimilation into soil by bioturbation as a function of air temperature and dung moisture. We validated that the model can accurately predict rates of dung disappearance, using data from 12 published studies. The model also simulates four pools of inorganic and organic P, P mineralisation to water-extractable P, leaching of dung water-extractable P into soil by rain, and loss of dissolved inorganic P in runoff. We validated the ability of the model to reliably simulate these P processes, using data from six published dung P transformation studies and six runoff studies. Overall, the model represents a novel approach for assessing the environmental impact of grazing dairy and beef cattle. Research should investigate the impact of dung deposition rate as a function of time and animal diet and type, where deposition occurs relative to runoff movement, weather conditions, and the ability of dung pad crusting to reduce P release to runoff.