Dung Pats Research Articles

Correlation between Coleoptera abundance in cattle excrements and pesticide contamination of nature conservation areas grazed by cattle

The aim of this study was to explore the relationship between pesticide contamination at 16 locations in 14 Dutch nature conservation areas and the abundance of Coleoptera (among which dung beetles) in excrements of grazing cattle. A wide spectrum of pesticides was measured in soil, vegetation and excrements of cattle, obtained from all locations. In the fresh dung pats sampled for chemical analysis, beetle numbers were counted and beetle species were identified. In total, 31 different pesticides (including some metabolites) were detected: 14 in fresh excrements, 17 in soil and 20 in vegetation. Total pesticide concentrations in soil, vegetation and excrements varied between 2.6 and 200 μg kg −1 dry matter. In vegetation, the most frequently encountered classes of pesticides (including some of their metabolites) were fungicides (9), herbicides (4) and insecticides (6). The total number of Coleoptera beetles in dung pats correlated negatively with the total concentration of insecticides in vegetation (Kendall's τ −0.501 at p < 0.05). The total concentrations of herbicides and fungicides were not statistically significant correlated with Coleoptera beetle numbers in the dung pats. Yet, the concentration of one single herbicide, viz. chlorpropham in vegetation correlated significantly negative with Coleoptera counts (Kendall's τ −0.603 at p < 0.01).

Experimental evidence that dung beetles benefit from reduced ivermectin in targeted treatment of livestock parasites

Anthelmintic residues in livestock dung can adversely affect beneficial organisms. Targeted selective treatment (TST) of a reduced proportion of livestock with anthelmintics can slow resistance development in gastrointestinal nematodes by providing residue-free dung which could also benefit non-target organisms. We tested effects of TST on survival and reproduction of the dung beetle Onthophagus taurus (Scarabaeidae) in a factorial glasshouse experiment (Experimental treatments: five TST levels, 0.00, 0.25, 0.50, 0.75, 1.00 x four ivermectin concentrations, 125, 250, 375, 500 ppb). Each mesocosm comprised a 60 L bin containing sand, four dung pats and six pairs of adult beetles (F0 generation). No effects of TST level and ivermectin concentration on mortality of F0 adults after one week were observed. F0 adult brood ball production was affected by TST level, particularly at high ivermectin concentrations. Brood ball production increased as more untreated pats became available, with greater increases at higher ivermectin concentrations. We tested for evidence of a reported attraction of dung beetles to ivermectin-treated dung using a novel glitter-marker to trace the origin of dung used in brood balls. Where mesocosms contained both dung types, the proportion of brood balls created from untreated dung showed no statistical difference from the null expectation based on untreated dung availability in the mesocosm. Emergence of F1 adults was affected by the increase in TST, with this effect dependent on concentration. Treatments with concentrations of 250–500 ppb had the lowest emergence rates (ca. 5–20 % in mesocosms where all dung pats were treated) but emergence rates increased with TST level, reaching 68–88 % emergence where no dung pats were treated with ivermectin. Ivermectin-induced mortality occurred predominantly at egg and first instar stages. TST can provide refuges for dung beetles offering a strategy for livestock producers to maintain livestock welfare whilst benefiting from ecosystem services provided by important insects.

A Case Study on Seasonal Behaviour of Aphodius elegans Allibert an Endocoprid Dung Beetle

Dung beetles (Scarabaeidae) classified into endocoprid, paracoprid, and telecoprid beetles, are fascinating insects with various behaviors. The study focuses on behaviour of endocoprid beetles Aphodius elegans Allibert, found in Bumdeling, Trashi Yangts Bhutan. The observational and scan sampling methods were employed during the study. These beetles locate dung using antennae and dig inside it, resembling a boat propelled by oars. They are active during warm weather and bury themselves under dung during cold. Beetles defecate semi solid feces after dung foraging. They mimic death as defensive and antipredator behaviour. They prefer moist dung pats for burial and use repeated attempts and strongholds of hindwings to initiate flight. This study substantiates the diverse fascinating behaviors of a less-focused group of insects to gain a deeper understanding of their interactions with ecology.

A Survey of the Dung-Dwelling Arthropod Community in the Pastures of the Northern Plains.

Grassland ecosystems of the Northern Plains have changed substantially since European settlement began in the latter half of the 19th century. This has led to significant changes to the dung-dwelling arthropod community in the region. As humans continue to modify large portions of the landscape, inventories of ecologically significant communities are important to collect in order to monitor the long-term effects of anthropogenic biomes. We conducted a survey of the arthropod community dwelling in cattle dung from 40 pastures extending from northeast South Dakota to central North Dakota during the 2019 and 2020 grazing seasons. In sum, 51,283 specimens were collected from 596 dung pats, comprising a community of 22 orders. Coleoptera, Diptera, and Hymenoptera contributed to the majority (94.5%) of the community abundance. The mean pest abundance was low per pat (0.43 adult pests/pat), with 80% of the pats not containing any adult pest. Ecologically beneficial dung-feeding beetles, predators, and parasitoids were abundant in the region, but it was an inconsistent community, which may hinder ecosystem services. This highlights the need for future work to understand the mechanisms to increase the consistency of dung pat colonization for improved consistency of ecosystem services in the region.

Effects of ivermectin on soil nutrient cycling, plant biomass, and dung beetle abundance

Ivermectin, a commonly used parasiticide, is known to affect dung beetle abundance when present in cattle dung. In this experimental study, we explicitly manipulated ivermectin concentrations in dung pats to examine its effects on dung beetle abundance, soil properties, and plant growth throughout the growing seasons of spring and summer in a western South Dakota grassland. Dung pats containing zero, low (2 mg/kg), and high (10 mg/kg) concentrations of ivermectin were strategically placed in the grassland in summer 2019 and spring 2021. Over a period of 63 days, we monitored changes in the nitrogen content of dung, soil, plants, as well as the abundance of dung beetles, and plant biomass. Our findings indicated that beetle abundance was 50% greater in dung pats without ivermectin, especially when the dung was fresh. However, ivermectin concentrations did not significantly alter the nitrogen content in dung and plants across both seasons, nor was there a discernible effect on plant biomass, despite the pronounced impact on dung beetle abundance.

Physical and bio-control methodologies for integrated management of buffalo fly-Haematobia exigua (Diptera: Muscidae)

Haematobia exigua, the buffalo fly, is a common ectoparasite of buffaloes and cattle in India causing economic losses and underlines the necessity of effective control strategies against them. The present study was planned to evaluate larvicidal activity of few methods for physical and biological control for integarated management of Haematobia exigua flies. Out of four bacterial bio-control agents evaluated by in-vitro assay and Probit analysis, two bacteria i. e. Bacillus thuringiensis var israelensis and Bacillus thuringiensis var kurstaki showed excellent larvicidal activity against H. exigua with LC50 value of 134 and 135 mg per liter of water respectively. Whereas, other two bacteria i. e. Bacillus weihenstephanensis WSBC and KBAB4 failed to show desired larvicidal activity. It can be concluded that B ti and B tk have future as effective bacterial agents (BCAs) in the control and integrated management of buffalo and horn fly. An experiment was conducted in the laboratory and on field for judging the efficacy of a physical method of tightly covering dung pats with polythene sheet for control of larvae of H. exigua. The laboratory result showed only 14.73% larvae were survived and developed per 100 gm of the faeces in the pot covered with polythene sheet as against significantly higher number 78.33% in the control group. During field trial, average larval count from dung pits before the experiment was 86.33 per 250 gm of faeces and it has been significantly reduced to 11.80 after covered with polythene sheets for two weeks. It indicated that physical method of covering the dung pits works immensely and thus can be inducted in IPM program as one of the effective physical control alternatives.

The Influences of Rainfall Intensity and Timing on the Assemblage of Dung Beetles and the Rate of Dung Removal in an Alpine Meadow.

Changes in precipitation patterns, including rainfall intensity and rainfall timing, have been extensively demonstrated to impact biological processes and associated ecosystem functions. However, less attention has been paid to the effects of rainfall intensity and rainfall timing on the assembly of detritivore communities and the decomposition rate of detritus such as animal dung. In a grazed alpine meadow on the eastern Qinghai-Tibet Plateau, we conducted a manipulative experiment involving two levels of rainfall intensity (heavy rainfall, 1000 mL/5 min; light rainfall, 100 mL/5 min) and five levels of rainfall timing (0, 2, 4, 24, and 48 h after yak dung deposition). The aim was to determine the effects of rainfall intensity, timing, and their interaction on the assemblage of dung beetles and dung removal rate during the early stage (i.e., 96 h after yak dung deposition) of dung decomposition. Light rainfall significantly increased species richness in the treatment of 48 h after dung pats were deposited. Heavy rainfall significantly decreased beetle abundance in both the 0 h and 48 h treatments while light rainfall had no effect on beetle abundance. Dung mass loss was significant lower in the 2 h treatment compared to other treatments regardless of rainfall intensity. The structural equation model further revealed that the species richness of dung beetles and dung mass loss were significantly affected by rainfall timing but not by rainfall intensity. However, no significant relationships were observed between any variables examined. These findings suggest that changes in precipitation patterns can influence both the structure of dung beetles and the rate of dung decomposition but may also decouple their relationship under a certain circumstance. Therefore, it is crucial to pay greater attention to fully understand local variability between the biological processes and ecosystem functions within a global climate change scenario.

Effects of Deforestation on Foraging Behavior, Ectoparasites, and Adult Survival in the Vulnerable La Selle Thrush, Turdus swalesi, in Haiti

Although range-restricted Neotropical bird species are highly endangered, little is known about their ability to cope with environmental disturbance. We studied the vulnerable, Hispaniola- endemic La Selle Thrush (LST), Turdus swalesi, in a protected forested area in Haiti threatened by agriculture, livestock and logging. We used capture–mark–recapture, visual observations, and camera traps to document foraging ecology and estimate adult survival over 26 months. LST foraged mainly in deciduous woodlots. However, some individuals regularly foraged on or around dung pats in fallow pastures, whereas no other ground-dwelling bird species was observed to do so. Coincidently, 16.5% of 79 mist-netted LST harbored Ixodid ticks, compared to none of the 2131 individuals belonging to 29 other species mist-netted in the area. This suggests that infestation with ticks might come as a cost of opportunistically exploiting a new food resource. Apparent annual adult survival rate was independent of sex, and varied between 0.393 and 0.440, depending on the inclusion of a transience effect in our models. This low value was possibly due to “permanent” emigration from the site during the study. We discuss the potential effects of deforestation on the ecology and demography of LST and make recommendations for future conservation-oriented research in Haiti.

A simple technique to assess resource use in dung beetle breeding studies

Abstract Current methods for identifying resource preferences in dung beetles are based on above‐ground trials. Although useful, these methods do not directly investigate resource provisioning of offspring below ground, missing an important part of dung beetle ecology. We tested the potential for UV‐fluorescent and non‐fluorescent coloured glitters to be used as markers for tracing the origin of dung incorporated into brood balls (dung shaped by parental beetles enclosing an egg), and so aid in a more complete understanding of resource use in dung beetles. We tested the effect of glitter addition on brood ball production in two species of tunnelling dung beetles, Onthophagus taurus and Euoniticellus fulvus. There was no effect of glitter addition on brood ball production during no‐choice tests for each species: both species made a similar number of brood balls, regardless of glitter presence or glitter colour. In a separate choice trial, O. taurus showed no preference for dung when presented with four dung pats containing four unique glitter colours. Here we show that glitter can be used as an effective marker of individual brood ball origin in tunnelling dung beetles. This method provides a useful tool for tracking below ground resource use and larval provisioning experiments in dung beetles.

Trickle-down effects of the cattle parasiticide ivermectin on soil microfauna on a prairie grassland

Ivermectin is a veterinary drug that is used globally to control internal and external cattle parasites. Dung of cattle treated with ivermectin contains residues that may transfer from the dung pat into the soil to affect soil organisms. We examined the effects of ivermectin in cattle dung on collembolans, nematodes and five taxonomic groups of mites in soils of a native grassland in southern Alberta, Canada. The trial, conducted in 2016 and repeated in 2017, comprised three treatments: (i) dung spiked with ivermectin and placed on soil; (ii) dung without ivermectin and placed on soil; and (iii) bare soil. Soil cores were taken beneath and adjacent to dung pats 1, 2, 4, 8, 12 and 16 weeks after dung placement and their microfauna quantified. Both generalized linear modeling and path modeling showed that dung without ivermectin increased the abundances of all the taxa relative to bare soil. However, these increases were at least partially negated for nematodes, Mesostigmata and Oribatida if the dung contained ivermectin. Path modeling also revealed unidirectional positive associations between some taxa: from Prostigmata (non-Tydeidae) to Collembola, from Acaridae to Prostigmata (both Tydeidae and non-Tydeidae), and from Mesostigmata to Oribatida. Therefore, deposition of fresh cattle dung enhanced the abundance of all microfauna for up to 16 weeks post-deposition, probably in response to an influx of nutrients and moisture. However, ivermectin in the dung reduced this benefit for three of the seven taxa.

Macrocyclic lactone residues in cattle dung result in a sharp decline in the population of dung beetles in the rangelands of northern China

Dung beetles perform important ecosystem functions including livestock dung removal, nutrient recycling and parasite control. However, more research is being done on the effects of veterinary drug residues on dung beetles due to the widespread usage of macrocyclic lactone (ML). While a number of research on this topic have been published in Europe, Africa and America, few have been in Asia. In the past decade, standard veterinary antibiotics administration in livestock grazing systems in the rangelands of northern China has included ML. In the present study, the abundance, species richness, diversity, and evenness of dung beetles in the rangelands of northern China in 2020 were examined and compared to the reference data from 2010, when parasiticide had never been used, to better understand the changes in dung beetle communities after the long-term use of parasiticides. The abundance and diversity of dung beetle populations in the current three rangelands in northern China were first investigated using a baited-trap experiment. The findings revealed a 67.3 % decrease in dung beetle abundance and a shift in the dominant species from Aphodiidae to Staphylinidae. Cattle dung on the three studied rangelands included high ML residues ranging from 22.7 ppb to 130.1 ppb. According to the results of the correlation analysis, the beetle abundance and ML residues in cattle dung were negatively correlated. In the meantime, the findings of a field examination of undecomposed cattle dung on 34 rangelands in northern China revealed that the coverage rate of dried cattle dung pats ranged from 2 % to 6 % on 24 rangelands and reached above 10 % on four rangelands. According to the current findings, the decrease in cattle dung beetles would slow down the decomposition of cattle dung pats and decrease the available grazing area. Therefore, the dung beetle community in the rangelands of northern China would be negatively impacted by the frequent administration of ML to cattle. This would result in significant changes to the biogeochemical cycle of rangeland and had a negative impact on the development of local husbandry. During rangeland management, more attention should be given to the dynamic changes of coprovorous insects and the application of veterinary antibiotics.

Nitrogen translocation by Highland cattle grazing in Alnus viridis-encroached pastures

During the last decades, Alnus viridis has expanded over former montane pastures and meadows, due to land use and abandonment. This nitrogen-fixing woody species has triggered negative agro-environmental impacts, such as nitrogen (N) leaching, soil acidification and a reduced biodiversity. The aim of this study was to estimate the N translocation from A. viridis-encroached areas to adjacent open pastures by Highland cattle. In 2019 and 2020, Highland cattle herds equipped with GPS collars were placed in four A. viridis-encroached paddocks across Italy and Switzerland. The N content was measured in A. viridis leaves, herbaceous vegetation, and cattle dung pats, which were collected throughout the grazing season. Using GPS locations and collar activity sensors, livestock activity phases were discriminated. The N ingested by cattle was estimated through the N content of herbaceous vegetation and A. viridis leaves of vegetation patches visited by cattle during 24 h before dung sampling (N24H). The N content of herbaceous vegetation significantly increased with increasing A. viridis cover. The average N content in dung pats (31.2 ± 3.4 g.kg−1 DM) was higher than average values from literature on grazing cattle. Moreover, it was positively related to the N24H. Most of this N (29.5 ± 10.3 kg ha−1 yr−1) was translocated towards resting areas, which generally occurred on flat open pastures. Our results highlight the potential of Highland cattle to effectively translocate part of the ingested N from A. viridis-encroached towards targeted open areas, thus bringing new perspective for forage yield and quality improvement in the long-term.

Forest conversion into pasture selects dung beetle traits at different biological scales depending on species pool composition.

The conversion of forests into open areas has large effects on the diversity and structure of native communities. The intensity of these effects may vary between regions, depending on the existence of native species adapted to open habitats in the regional pool or the time since habitat change.We assess the differences in species richness and functional diversity of dung beetle communities (Coleoptera: Scarabaeinae) between native forests and novel pasturelands of the Atlantic Forest and the Cerrado, two biomes with contrasting histories of human occupation in Brazil. We conducted standardized surveys in seven forest fragments and adjacent pastures in each region and measured 14 traits in individuals collected in each type of habitat at each particular site. We calculated functional richness, functional evenness, functional divergence, and community-weighted mean of traits for each area, and analyzed individual variation through nested variance decomposition and Trait Statistics.Communities were richer and more numerous at the Cerrado. We did not find any consistent relationship between functional diversity and forest conversion beyond the changes in species diversity. Although landscape changes were more recent at the Cerrado, the colonization of the new habitat by native species already adapted to open habitats lessens the functional loss in this biome. This indicates that habitat change's effects on trait diversity depend on the regional species pool rather than on time since land conversion.Forest conversion effects were primarily due to internal filtering. The effects of external filtering only appear at the intraspecific variance level, with contrasting differences between the Cerrado, where traits related to relocation behavior and size are selected, and the Atlantic Forest, where selection operates for traits related to relocation behavior and flight. These results evidence the importance of considering individual variance to address the responses of dung beetle communities to forest conversion.

Resident and migrant birds use livestock dung pats for foraging

Resident and migrant birds use livestock dung pats for foraging

Residues of pesticides in dairy cow rations and fly treatments reduce the number of Coleoptera in dung

There is a global pattern of a decline in insect abundance and diversity. The presence of residues of pesticides in animal feed and fly treatments results in polluted animal dung, which may hamper the survival of insects feeding and breeding in and on dung. To study the route from pesticide contamination in the feed and the dung to insect survival in dung pats, two experiments were performed. In Experiment 1, the feed and dung of dairy cows were collected on eight Dutch dairy farms (six conventional, two organic). All the feeds in the ration as well as the dung were analysed for the presence of pesticides. In Experiment 2, dung was collected from a herd of dairy cows and was spiked with four concentrations of deltamethrin. In both experiments, a field experiment was implemented with artificial dung pats of 2 kg of fresh dung. The dung pats were retrieved after 7 and 14 days (Experiment 1), or 7, 14, 21, and 35 days (Experiment 2), and invertebrates in the dung were counted. A total of 70 pesticides were detected in the different types of feed of the eight farms. The concentration of pesticides in the dung was on average 423 µg kg−1 DM (range of 112–1980 µg kg−1 DM). In Experiment 1, the number of Coleoptera present in dung was negatively correlated with the pesticide concentration, and more Coleoptera were present in the dung of organic farms (23.7 on organic farms vs. 11.4 Coleoptera on conventional farms, per 500 g freshly deposited dung). In Experiment 2, the dung which was not spiked with deltamethrin contained more than twice as many Coleoptera larvae and adults (5.6 Coleoptera per 500 g freshly deposited dung on treatment without deltamethrin vs. 2.2 with highest concentration of deltamethrin). We conclude that pesticides are widely present in feed for dairy cows and that a number of these pesticides are transferred to dung. The pesticides have a negative effect on the number of Coleoptera and as a consequence may also affect ecosystem services such as the disappearance of dung pats and the presence of insects in dung pats as feed for farm birds or bats.

Temporal changes in the nutrient content of cattle dung in the Nebraska Sandhills ecosystem

Dung excreted by cattle composes a significant portion of the nutrient inputs in a grazed ecosystem and can have wide-ranging effects on soil properties and vegetation. However, little research has been conducted on the nutrient dynamics of excreted dung in situ that has not been disturbed prior to field sampling. In this study, we analyzed 294 dung pats (1–24 days old) collected from a Nebraska Sandhills meadow to determine water-extractable organic carbon (WEOC), water-extractable nitrogen (WEN), water-extractable phosphorus (WEP), and percent dry matter (DM) changes over time. In addition, we investigated if sample handling - frozen storage – and the formation of surface crust during dung field drying affect dung nutrient concentrations. Dung WEOC and WEN both followed exponential decay curves of nutrient loss over time and were modeled as a function of age. In contrast, WEP was poorly correlated with age. The percent dry matter in conjunction with sample WEOC concentration were stronger determinants of WEP than age alone. Freezing samples prior to analysis increased WEOC (37–98%) and WEN (37–123%), but lowered WEP (0.8–65%) compared to the samples from the same dung pat analyzed fresh. The dry surface crusts of dung pats had higher WEOC (98–112%) and WEN (112%) compared to moist interiors (on average, 3 cm from surface). This research provides evidence that dung nutrient concentrations decreased by 73% (WEOC) and 76% (WEN) over 24 days and shows that frozen storage and subsequent thawing for analysis, as well as crust formation during field drying, can significantly affect dung nutrient concentrations and spatial partitioning of dung nutrients.

Pasture dragging fails to reliably suppress the emergence of horn flies (Haematobia irritans) and face flies (Musca autumnalis) from dung pats in a Mid-Atlantic North American climate.

The beef industry endures major economic losses from a complex of flies that feed on bovine blood and mucus. For cattle on pasture, the most important of these pests are horn flies (Haematobia irritans [L.] [Diptera: Muscidae]) and face flies (Musca autumnalis [Diptera: Muscidae] De Geer). Pasture dragging to spread manure pats has been promoted as a management tactic for these species because their larvae inhabit bovine manure pats, but the efficacy of this practice has not been empirically validated. Spreading pats might promote fly mortality through desiccation or overheating, but these processes are weather-dependent and warrant testing in disparate climates. We evaluated pasture dragging effects while monitoring for weather interactions throughout nine experiment rounds in summers of 2018 and 2020 in Pennsylvania, USA. The manure spreading treatments increased pat surface area up to 300% but failed to significantly reduce emergence of horn flies and face flies as compared to controls. In contrast, precipitation and temperature were significant predictors in fly emergence models. Surprisingly, face fly emergence was significantly elevated in dragged pats twice in 2020. These data call for a reevaluation of pasture dragging as a management technique for horn flies and face flies across a range of climates.

Soil Dynamics and Nitrogen Absorption by a Natural Grassland under Cow Urine and Dung Patches in an Andisol in Southern Chile

The objective of this study was to assess N dynamics in the soil, and the response in regard to dry matter yield (DM yield; kg·DM·ha−1), N yield (g·N·m−2) and N concentration (g·N·kg−1 DM) under urine patches and dung pats and in the affected zone of the grassland soil over 304 days. The amount of N under the urine and dung patches increased until day 10 and then started to decrease until the end of the experiment, reaching control treatment levels. The DM yield in the urine patch zone and the 0–10 cm zone around the dung pat was higher than in the control treatment throughout the evaluated period, while in the 0–30 cm zone around the urine patch and the 10–20 cm zone around the dung pat the DM yield was negatively affected by the application of excreta. The maximum accumulated N yield was up to two times higher than the control in the 0–10 cm zone of the dung pat, while the mean concentration of N throughout the period was 42% higher than the control for the “urine patch” zone and 47% higher in the 0–10 cm area around the dung pat. The total absorbed N was 19% and 15% for urine and dung excreta, respectively. Further research is needed to explain the variables that might affect the results obtained, and it is necessary to evaluate the botanical composition as a factor that contributes to this effect.

Dung beetle community composition affects dung turnover in subtropical US grasslands.

An important service in many ecosystems is the turnover and degradation of dung deposited by cattle. Dung beetles are the primary group of insects responsible for dung turnover, and factors affecting their abundance and distribution thus impact dung degradation. Lands lost to grazing due to dung buildup and pasture contamination total millions of acres per year in US pastures.We evaluated the structural differences in dung beetle assemblages in natural grasslands versus a managed agroecosystem in subtropical southeastern Florida (USA). We measured the direct effect of dung longevity when dung beetle fauna normally inhabiting dung pats were excluded.Our results indicate dung beetle abundance, functional diversity, and species richness have a substantial impact on the rate of dung turnover in subtropical pastoral lands with ~70% of dung removed from the soil surface after three months. Functional diversity and evenness did not have a significant positive effect on dung removal in managed, versus natural grasslands demonstrating a strong relationship between dung beetle assemblage composition and delivery of a key ecological process, dung degradation.We suggest the importance of trees, which provide a thermal refuge for beetles, should be dispersed within matrixes of open pasture areas and within proximity to adjacent closed‐canopy hammocks to facilitate the exchange of dung beetles between habitats and therefore maintain the provisioning of dung degradation services by dung beetle assemblages.

Dweller and tunneler dung beetles synergistically accelerate decomposition of cattle and horse dung in a semi-arid steppe

Aboveground and belowground invertebrates play a key role in decomposition of organic matter in terrestrial ecosystems. Dung beetles are well known for their functions in breaking down and transporting ungulate dung into soils thus promoting dung decomposition. However, the effects of functionally different dung beetles on the decomposition processes of the dung from different ungulates remain less explored. We did an in situ experiment using the 'dung and soil' mesocosm to investigate the separate and combined effects of two functionally contrasting dung beetle species, a dweller Aphodius sordecens and a tunneler Onthophagus gibbulus, on the decomposition processes of the dung from horse and cattle. We determined the changes in dung mass, dung C and N contents, microbial respiration from the 'dung and soil' mesocosm or from the soil beneath the dung pats, and examined the amount of dung balls transferred by beetles into different soil layers, under five dung beetle treatments (C – soil, no dung nor beetles; D – dung on soil with no beetles; DB - dung on soil with dweller beetles; TB - dung on soil with tunneler beetles; DTB - dung on soil with dweller and tunneler beetles) were applied to the dung of two major grazers with different digestive systems in native steppes in northern China, over a two-month period following dung deposition. We found that (1) tunneler beetles (in TB and DTB) significantly enhanced the dry mass loss of cattle dung but not horse dung. (2) Dung C and N contents declined more rapidly with the presence of any dung beetle species (DB-DTB) than that without (D); and dung N content showed different decreasing rates between horse and cattle dung in different decomposition periods. (3) The presence of the two functionally contrasting dung beetle species together had a synergistic, positive effect on soil microbial respiration and thus on the decomposition rate of soil organic matter; however, no significant effects of beetles on net microbial respiration was detected in the 'dung + soil' mesocosm. (4) The direct effect of dung beetles on dung mass loss was stronger for cattle dung than for horse dung. In contrast, the decline in moisture content of horse dung with decomposition time affected the microbial respiration in dung, and thus indirectly affected the dry mass loss and the C and N contents. Our results suggest it critically important to incorporate the functions of soil invertebrates into nutrient cycling models to improve their accuracy, and to promote invertebrate diversity in grazed grassland to maintain ecosystem health and services.