Landscape diversity of pasture dung beetle communities in the central region of mainland Japan and implications for conservation management

We studied the diversity of dung beetle communities in Japanese pastures to identify the factors that maintain or enhance the diversity of dung beetles at a landscape scale. We surveyed dung beetles from 17 pastures located in the northeastern part of Tochigi Prefecture, which is in the center of mainland Japan. From 1999 to 2001, surveys were conducted during the 6-month grazing period (May to October) by using dung baited basket traps. We also collected information about the environmental conditions and pasture management practices. Twenty-five dung beetle species belonging to Geotrupinae, Scarabaeinae, and Aphodiinae (including 13 tunneler and 12 dweller species) were recorded. The abundance of dweller species decreased with increasing elevation, possibly because of the effect of rainfall, whereas the species richness of tunneler species was affected by cattle disturbance and soil condition. Beetle species richness significantly increased with the number of years that the pastures had been grazed. Ivermectin administration did not appear to have any adverse effect on dung beetle abundance, species richness, or species diversity. The dung beetle datasets of the current study (including specific tunneler and dweller beetle groups) supported the widely documented positive relationship between local abundance and species distribution ranges. The within pasture, within area, and between area hierarchical additive partitioning of regional total diversity indicated that landscape-scale management should be implemented to conserve the regional diversity of the dung beetle communities inhabiting Japanese pastures.     

Effects of dung-pad conditions and density on coprophagous beetle assemblages in a Mediterranean rangeland

Dung beetles highly depend on the ephemeral microhabitat dung which is food resource and larval habitat at the same time. Environmental conditions surrounding a dung pad, such as vegetation structure, have an impact on dung beetle assemblages. We investigated the influence of dung conditions and surrounding habitat characteristics on Mediterranean dung beetle assemblages in a permanently grazed landscape in northern Sardinia. We sampled the dung beetle assemblages of donkey and horse dung in three different vegetation types and assessed species richness and abundance of dung beetles. Species richness was determined by dung and surrounding habitat conditions, whereas abundance was solely affected by dung conditions. However, species richness and abundance decreased with increasing dung density. The effect of dung density on species richness varied depending on vegetation type, with dry grassland exhibiting the highest number of dung beetles species at high dung density. Species composition in dung pads was influenced by abiotic factors with dwellers being negatively affected by increasing dung-pad temperature. Our results underline the importance of diverse vegetation, particularly with respect to the complexity of vegetation which interrelates with the microclimate. Furthermore, our findings illustrate the negative effect of high dung densities on dung beetle assemblages, suggesting that the degree of the intensity of use by grazing animals is important when considering measures for the conservation of dung beetles.     

Seedling establishment after endozoochory in disturbed and undisturbed grasslands

Local plant community composition and structure may be largely influenced by germination and seedling establishment from seeds dispersed in animal dung, through seed input, gap creation and nutrient enrichment. With an experimental approach we assessed (1) what the effect is of dung deposition on the number of seedlings in the plant community 3 months and 1 year after dung deposition, (2) what the effect is of this seedling establishment on the local plant community characteristics such as species richness and (3) if this effect interacts with large-scale soil disturbance which removes the close canopy, such as sod-cutting. Viable seeds of monocotylous species were abundantly present in the dung, and dung deposition led to a higher number of monocotylous seedlings after 3 months. However, this effect was no longer significant after 1 year. Moreover, the proportion of viable monocotylous seeds that effectively established in the field after 3 months was less than 5%. A lower number of viable seeds of the less-dominant dicotylous species was dispersed in the dung but they had a higher cover and species richness after 1 year. This resulted in an increased total small-scale species richness and diversity after dung deposition through a decreasing dominance of monocotylous species. Sod-cutting had a pronounced effect on seedling emergence: viable seeds dispersed by dung had a higher probability of successful establishment when the dung was deposited in large gaps. This indicates that an increase of safe sites associated with disturbance strengthens the effects of seed dispersal and gap creation by dung deposition.     

Degraded lands worth protecting: the biological importance of Southeast Asia's repeatedly logged forests

Southeast Asia is a hotspot of imperilled biodiversity, owing to extensive logging and forest conversion to oil palm agriculture. The degraded forests that remain after multiple rounds of intensive logging are often assumed to be of little conservation value; consequently, there has been no concerted effort to prevent them from being converted to oil palm. However, no study has quantified the biodiversity of repeatedly logged forests. We compare the species richness and composition of birds and dung beetles within unlogged (primary), once-logged and twice-logged forests in Sabah, Borneo. Logging had little effect on the overall richness of birds. Dung beetle richness declined following once-logging but did not decline further after twice-logging. The species composition of bird and dung beetle communities was altered, particularly after the second logging rotation, but globally imperilled bird species (IUCN Red List) did not decline further after twice-logging. Remarkably, over 75 per cent of bird and dung beetle species found in unlogged forest persisted within twice-logged forest. Although twice-logged forests have less biological value than primary and once-logged forests, they clearly provide important habitat for numerous bird and dung beetle species. Preventing these degraded forests from being converted to oil palm should be a priority of policy-makers and conservationists.     

Potential and realised contribution of endozoochory to seedling establishment

Many plant species have been shown to be dispersed by large herbivores through endozoochory, but there have been few studies that have demonstrated the ecological significance of this dispersal method. Known quantities of seeds were fed to sheep and the emergence of seeds germinating from dung in the field and glasshouse were compared with emergence in the field after direct sowing. All 12 species studied showed potential endozoochory as they germinated and grew from dung in the glasshouse. Six species showed no emergence in the field from either dung or direct sowing. Of the remaining, three did not emerge from dung in the field but did from direct sowing indicating a very high cost of dispersal (one other species showed this pattern but not significantly), one emerged in the field from dung but at comparatively low rates and one showed no cost to endozoochory as it emerged equally well from dung or after direct sowing. The results indicate that potential endozoochory, as measured by germination from dung in the glasshouse, over-estimates likely rates of establishment in the field. The results also indicate that there are potentially high costs to endozoochory that have to be balanced against the benefits of long-distance dispersal by large herbivores.     

Community assembly and biomass production in regularly and never weeded experimental grasslands

We studied the natural colonisation of new species in experimental grasslands varying in plant species richness (from 1 to 60) and plant functional group richness (from 1 to 4) in either regularly or never weeded subplots during the first 3 years after establishment. Sown species established successfully, with no differences in species richness or their relative abundances between the regularly and never weeded subplots during the study period. Aboveground biomass of sown species increased with increasing sown species richness in both treatments. While a positive relationship between sown species richness and total aboveground biomass (including colonising species) existed in the 2nd year after sowing in the regularly and never weeded subplots, this positive relationship decayed in the 3rd year in the never weeded subplots because of a higher biomass of colonising species in species-poor mixtures. Total aboveground biomass varied independently of total species richness 3 years after sowing in both treatments. Jaccard similarity of coloniser species composition between regularly and never weeded subplots decreased from the 2nd to the 3rd year, indicating a divergence in coloniser species composition. Coloniser immigration and turnover rates were higher in regularly weeded subplots, confirming that weeding counteracts species saturation and increases the chance that new colonisers would establish. Although our study shows that low diversity plant communities are unstable and converge to higher levels of biodiversity, the effects of initially sown species on community composition persisted 3 years after sowing even when allowing for succession, suggesting that colonising species mainly filled empty niche space.     

Feral horses dung piles as potential invasion windows for alien plant species in natural grasslands

Small scale disturbances could act as patches that provide sites for the colonization of competitively inferior species, promoting the establishment of non-native species in some cases. We analyzed the vegetation associated with feral horse dung piles in montane pampas grasslands in Mid-East Argentina and described the changes following their abandonment, evaluating whether dung piles act as invasion windows, allowing the entrance of alien plant species. We estimated the portion of the study area directly covered by horse manure and dung height was used to estimate the time elapsed after the abandonment of each pile. Vegetation replacement on dung piles of different ages was assessed and compared with grassland controls using discriminant analysis. We used regression analysis to look for changes in vegetation cover, species richness, species diversity and evenness in response to height (age) of the dung piles, and principal component analyses (PCA) to identify groups of plants associated with different successional stages. We compared cover of alien plant species on dung piles with grassland controls using one-way ANOVA. On average, 2.5% of the study area was covered by horse dung. Total vegetation cover, species richness, diversity and evenness increased after the piles were abandoned. Characteristic plant groups were associated with initial, middle and last phases of the studied succession. Vegetation on the dung piles significantly differed from that in grassland controls and two species were consistently associated with dung piles: the invasive Red Star Thistle, Centaurea calcitrapa, and a native grazing-intolerant grass, Nassella clarazii. Non-native species cover was also higher in dung piles than in control plots. Dung piles cover a significant portion of grassland area in our study site, produce significant changes in the vegetation and are associated with some invasive alien plants that could eventually colonize more pristine areas in the vicinity. On the other hand, they might represent refuges for palatable species, since horses seem to avoid them for grazing.     

Different Assembly Processes Drive Shifts in Species and Functional Composition in Experimental Grasslands Varying in Sown Diversity and Community History

Background

The prevalence of different biotic processes (limiting similarity, weaker competitor exclusion) and historical contingency due to priority effects are in the focus of ongoing discussions about community assembly and non-random functional trait distributions.

Methodology/Principal Findings

We experimentally manipulated assembly history in a grassland biodiversity experiment (Jena Experiment) by applying two factorially crossed split-plot treatments to all communities: (i) duration of weeding (never weeded since sowing or cessation of weeding after 3 or 6 years); (ii) seed addition (control vs. seed addition 4 years after sowing). Spontaneous colonization of new species in the control treatment without seed addition increased realized species richness and functional richness (FRic), indicating continuously denser packing of niches. Seed addition resulted in forced colonization and increased realized species richness, FRic, functional evenness (FEve) and functional divergence (FDiv), i.e. higher abundances of species with extreme trait values. Furthermore, the colonization of new species led to a decline in FEve through time, suggesting that weaker competitors were reduced in abundance or excluded. Communities with higher initial species richness or with longer time since cessation of weeding were more restricted in the entry of new species and showed smaller increases in FRic after seed addition than other communities. The two assembly-history treatments caused a divergence of species compositions within communities originally established with the same species. Communities originally established with different species converged in species richness and functional trait composition over time, but remained more distinct in species composition.

Conclusions/Significance

Contrasting biotic processes (limiting similarity, weaker competitor exclusion) increase functional convergence between communities initially established with different species. Historical contingency with regard to realized species compositions could not be eradicated by cessation of weeding or forced colonization and was still detectable 5 years after application of these treatments, providing evidence for the role of priority effects in community assembly.     

Wide corridors with much environmental heterogeneity best conserve high dung beetle and ant diversity

Landscape ecological networks (ENs) consist of landscape-scale conservation corridors that connect areas of high natural value within a production mosaic with protected areas (PAs). In South Africa, ENs have been implemented on a large spatial scale to offset the negative impacts of plantation forestry on indigenous grasslands. We focus on corridor width as a factor for conserving dung beetle and ant diversity within an EN. We also investigate the importance of natural environmental heterogeneity (elevation, vegetation type) and habitat quality (soil hardness, invasive alien plant density). We sampled dung beetles and ants in 30 corridors of different sizes, and at ten sites in a nearby PA. In addition, we also analysed dung beetles according to their feeding guild. Tunnelling dung beetle species richness increased with corridor width. Rolling dung beetle species richness was higher in the PA than in the corridors of the EN. The dung beetle assemblage within the EN differed from that within the PA. Corridors of various widths differed in ant composition but not in species richness. Furthermore, the PA and the EN differed in environmental variables, which contributed to differences in dung beetle species richness and assemblage composition. Within the EN, environmental heterogeneity across the landscape was more important than corridor width for driving species diversity of both dung beetles and ants. When planning future ENs, wide corridors (>280 m) that encompass as much natural heterogeneity across the landscape as possible will best conserve the range of local insect species.     

Re-creating Semi-natural Communities: Effect of Sowing Rate on Establishment of Calcareous Grassland

Restoration ecologists are increasingly aware of the potential to re-create chalk grassland on abandoned farmland. Success is often hampered by lack of desirable species in the seed bank and by poor dispersal from nearby sites. In certain schemes, the input of seed may be essential. Locally collected seed is desirable but availability is limited. We examined whether lower sowing rates than currently recommended may be successfully utilized, facilitating more-efficient use of available seed. Experimental plots on former agricultural land were sown at different rates in a randomized complete block, and the vegetation was surveyed for two years. We compared species richness and cover for chalk grassland plants and weeds - species not associated with chalk grassland communities. Values for cover and abundance were matched with data for communities of the British National Vegetation Classification (NVC). Species richness for chalk grassland plants increased with sowing rate and with time, although after two years there was no significant difference between the treatments sown at 0.4, 1.0, and 4.0 grams of seed per square meter. Weed species decreased with increasing rate and time. After two seasons, the vegetation on all treatment plots was similar to that of recognized NVC chalk grassland communities, while the controls were dominated by weeds and showed signs of developing into species-poor grassland. Higher rates rapidly eliminated weeds, but even a small inoculum of seed seemed to significantly enhance establishment of desirable plants and to reduce weed cover. We conclude that lower sowing rates would enable the desired vegetation to become established successfully, under appropriate conditions and management regimes. Lower rates allow for the re-creation of sizable areas using local seed, and they minimize damage to donor sites.     

Dung beetle assemblages on tropical land‐bridge islands: small island effect and vulnerable species

Aim Using dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) in a tropical land‐bridge island system, we test for the small island effect (SIE) in the species–area relationship and evaluate its effects on species richness and community composition. We also examine the determinants of species richness across island size and investigate the traits of dung beetle species in relation to their local extinction vulnerability following forest fragmentation. Location Lake Kenyir, a hydroelectric reservoir in north‐eastern Peninsular Malaysia. Methods We sampled dung beetles using human dung baited pitfall traps on 24 land‐bridge islands and three mainland sites. We used regression tree analyses to test for the SIE, as well as species traits related to local rarity, as an indication of extinction vulnerability. We employed generalized linear models (GLMs) to examine determinants for species richness at different scales and compared the results with those from conventional linear and breakpoint regressions. Community analyses included non‐metric multidimensional scaling, partial Mantel tests, nestedness analysis and abundance spectra. Results Regression tree analysis revealed an area threshold at 35.8 ha indicating an SIE. Tree basal area was the most important predictor of species richness on small islands (<35.8 ha). Results from GLMs supported these findings, with isolation and edge index also being important for small islands. The SIE also manifested in patterns of dung beetle community composition where communities on small islands (<35.8 ha) departed from those on the mainland and larger islands, and were highly variable with no significant nestedness, probably as a result of unexpected species occurrences on several small islands. The communities exhibited a low degree of spatial autocorrelation, suggesting that dispersal limitation plays a part in structuring dung beetle assemblages. Species with lower baseline density and an inability to forage on the forest edge were found to be rarer among sites and hence more prone to local extinction. Main conclusions We highlight the stochastic nature of dung beetle community composition on small islands and argue that this results in reduced ecosystem functionality. A better understanding of the minimum fragment size required for retaining functional ecological communities will be important for effective conservation management and the maintenance of tropical forest ecosystem stability.     

El Niño impacts on human-modified tropical forests: Consequences for dung beetle diversity and associated ecological processes

Our knowledge of how tropical forest biodiversity and functioning respond to anthropogenic and climate-associated stressors is limited. Research exploring El Niño impacts are scarce or based on single post-disturbance assessments, and few studies assess forests previously affected by anthropogenic disturbance. Focusing on dung beetles and associated ecological functions, we assessed (a) the ecological effects of a strong El Niño, (b) if post-El Niño beetle responses were influenced by previous forest disturbance, and (c) how these responses compare between forests impacted only by drought and those affected by both drought and fires. We sampled 30 Amazonian forest plots distributed across a gradient of human disturbance in 2010, 2016, and 2017—approximately 5 years before, and 3–6 and 15–18 months after the 2015–16 El Niño. We found 14,451 beetles from 98 species and quantified the beetle-mediated dispersal of >8,600 seed mimics and the removal of c. 30 kg of dung. All dung beetle responses (species richness, abundance, biomass, compositional similarity to pre-El Niño condition, and rates of dung removal and seed dispersal) declined after the 2015–16 El Niño, but the greatest immediate losses (i.e., in 2016) were observed within fire-affected forests. Previous forest disturbance also influenced post-El Niño dung beetle species richness, abundance, and species composition. We demonstrate that dung beetles and their ecological functions are negatively affected by climate-associated disturbances in human-modified Amazonian forests and suggest that the interaction between local anthropogenic and climate-related stressors merits further investigation.     

Dung preference and trophic association of dung beetles (Coleoptera: Scarabaeidae) in the moist forests of the South-western Ghats of the Indian subcontinent

First quantitative dung beetle-feeding trophic network analysis for the Oriental region is carried out by investigating trophic network interaction between dung beetles and mammal dung types in the moist forests of the Western Ghats a global biodiversity hot spot in south-western India. Dung-beetle assemblage associated with the dung of the prominent mammals, such as the macaque, boar, gaur, elephant and deer, showed differences in richness, abundance and composition among different dung types. Most dung beetles were generalists with low resource specificity and community-wide generalist feeding on herbivore and omnivore dung types. Dung beetles in the region displayed high species richness and abundance in boar dung. The high attraction and specificity of dung beetles towards the odoriferous boar dung indicate that the omnivore mammal Sus scrofa has a major role in maintaining the dung beetle community in the forests of the Western Ghats. Network interaction analysis shows that the vast majority in the assemblage are generalist species, and the few specialist species were all with low abundance. Low overall specialisation and low resource partitioning with high species richness is recorded in the assemblage. The assemblage's trophic level preference is reflected in the high dung specificity recorded in the omnivore and herbivore dung types.     

Forest complexity drives dung beetle assemblages along an edge-interior gradient in the southwest Amazon rainforest

1. The habitat heterogeneity hypothesis predicts that heterogeneous habitats may provide more niches and diverse ways of exploiting environmental resources, thereby allowing more species to coexist, persist and diversify. 2. We aimed to investigate how an edge-interior gradient related to forest complexity influences species composition, abundance and richness of dung beetles in the western Amazon rainforest. We expected dung beetle abundance and richness to increase along the forest edge-interior gradient, in accordance with the habitat heterogeneity hypothesis. We also expected strong changes in species composition driven by species turnover in the forest interior and nestedness along the forest edges. We sampled dung beetles using baited pitfall traps across an edge-interior gradient. We also assessed the variation in forest features along the edge-interior gradient to identify changes in forest complexity. 3. Both species richness and abundance of dung beetles increased along the forest edge-interior, following the gradient of forest complexity. The Sorensen dissimilarity of dung beetle assemblages was higher among sampling units placed near the forest edge, although neither turnover, nor nestedness was different between the extremes of the forest edge-interior gradient. There was a clear compositional change along the edge-interior gradient mostly driven by species turnover. Individual indicator value analysis revealed that species were strongly associated with the forest interior conditions. 4. The simplification of the Amazon rainforest near clearings causes compositional changes in dung beetle assemblages. These changes are characterised by species-poor and low-abundance assemblages and may impair dung beetle ecological functions and therefore forest recovery.     

Nesting strategies affect altitudinal distribution and habitat use in Alpine dung beetle communities

1. Dung beetles are key contributors to a suite of ecosystem services. Understanding the factors that dictate their distributions is a necessary step towards preventing negative impacts of biodiversity loss. 2. Alpine dung beetle communities were analysed along altitudinal gradients to assess how different components of the community, defined in terms of nesting strategy [dung‐ovipositing Aphodiidae (DOAs), soil‐ovipositing Aphodiidae (SOAs) and two paracoprid (PAR) groups, Geotrupidae and Scarabaeidae] and parameters relevant to dung removal rates (species richness, total biomass and functional diversity), are distributed, and to identify to which environmental factors they respond. 3. Species richness declined with altitude. There was no significant variation in functional diversity or total biomass in relation to altitude. There were significant variations when considered by nesting group: DOA species richness and biomass decreased, SOA biomass increased, and Geotrupidae biomass showed a non‐linear trend, as altitude increased. 4. Functional diversity and total species richness were positively related to vegetation cover. DOA species richness was highest in forest and scrub; SOA species richness was highest in grassland and PAR species richness was lowest in rocky areas. 5. Dung beetle species show different trends in species richness and biomass depending on nesting strategy. Management to promote the dung beetle community should include maintenance of a mosaic of habitat types. Given the likely importance of species richness and biomass to ecosystem functioning, and the complimentary effect of different dung beetle groups, such a strategy may protect and enhance the ecosystem services that Alpine dung beetles provide.     

Effect of dung beetle species richness and chemical perturbation on multiple ecosystem functions

1. The relationship between biodiversity and ecosystem functioning is typically positive but saturating, suggesting widespread functional redundancy within ecological communities. However, theory predicts that apparent redundancy can be reduced or removed when systems are perturbed, or when multifunctionality (the simultaneous delivery of multiple functions) is considered. 2. Manipulative experiments were used to test whether higher levels of dung beetle species richness enhanced individual functions and multifunctionality, and whether these relationships were influenced by perturbation (in this case, non‐target exposure to the veterinary anthelmintic ivermectin). The four ecosystem functions tested were dung removal, primary productivity, soil faunal feeding activity and reduction in soil bulk density. 3. For individual functions, perturbation had limited effects on functioning, with only dung removal significantly (negatively) affected. Species richness did not, on its own, explain significant variation in the delivery of individual functions. In the case of primary productivity, an interaction between richness and perturbation was found: species‐rich dung beetle assemblages enhanced forage growth in the unperturbed treatment, relative to the perturbed treatment. 4. Using a composite ‘multifunctionality index’ it was found that species‐rich dung beetle assemblages delivered marginally higher levels of multifunctionality in unperturbed conditions; however, this benefit was lost under perturbation. Using a relatively new and robust method of assessing diversity–multifunctionality relationships across a range of thresholds, no significant effect of species richness on multifunctionality was found.     

Monitoring the ecosystem service provided by dung beetles offers benefits over commonly used biodiversity metrics and a traditional trapping method

Surveying terrestrial invertebrates often requires lethal techniques that can also kill non-target vertebrates. Removing the desirable components of biodiversity is at odds with the philosophy of ecological restoration and biodiversity conservation more generally. Moreover, commonly used metrics generated by such survey approaches (e.g. abundance and species richness) are only indirectly related to the ecosystem services (e.g. pollination) that are often of primary interest. We examined the relationship between rates of dung removal (a direct measure of an ecosystem service) and dung beetle abundance and species richness in a temperate region of New South Wales, Australia, and examined if dung removal in revegetated riparian areas of different ages were trending monotonically toward rates in areas with mature native vegetation. Pellets of pig manure and conventional traps were left at study sites for 48 h to examine the relationships between rates of dung removal and dung beetle abundance and richness. Regressions of abundance and richness with average percent dung removal were positive and significant, demonstrating the potential of the method as a non-lethal proxy. While the dung removal method cannot determine the species responsible, percentage dung removal was more time-efficient, costing 4 min per sample, while abundance and richness cost 13 and 17 min, respectively. Despite variability among replicates of the same habitat type, the trajectory across the restoration gradient showed an increase from sites recently revegetated toward those with mature woody vegetation. We interpreted these results as a positive response of dung beetle activity and an indication of recovery of this ecosystem service. We argue that responses that can be collected efficiently such as dung removal should be used if restorationists have limited resources for data collection and analysis; non-specialists are involved; knowledge of ecosystem function is required, and animal ethics constrain options.     

Low local but high beta diversity of tropical forest dung beetles in Madagascar

Aims We have compared local (alpha) and regional (beta) species diversities of dung beetles in wet forests in the main tropical regions including Madagascar. Madagascar is exceptional in lacking native large herbivorous mammals which produce the key resource for dung beetles elsewhere. Location Central and South America, mainland Africa, Madagascar and Southeast Asia. Methods Trapping data on dung beetles and data on mammalian faunas were obtained from published and unpublished studies. We used our original data for Madagascar. Results Species richness of dung beetles and that of large‐bodied (> 15 mm length) species in particular were highly significantly explained by the regional number of large‐bodied (> 10 kg) mammals (R² from 50 to 80%). For a given pairwise spatial distance between two communities, beta diversity was significantly higher in Madagascar than elsewhere, explaining the very high total species richness in Madagascar in spite of low local diversity. Main conclusion The presence and numbers of large herbivorous mammals greatly influence the species richness of dung beetles in tropical wet forests. The lack of native large herbivores rather than a limited species pool explains the low local diversity in Madagascar. Exceptionally high beta diversity in Madagascar suggests a pattern of old radiation involving extensive allopatric speciation.     

Does an aridity and trophic resource gradient drive patterns of dung beetle food selection across the Botswana Kalahari?

1. Aridity gradients are paralleled by both reductions in resources and decreased species richness of animals. Across the aridity gradient of the Botswana Kalahari, a reduction in mammal species richness leads to reduced density and diversity of dung types, accompanied by reduced dung beetle species richness. We investigated whether this gradient also drives changes in dung beetle food type association and specialisation owing to a loss of some dung types to the arid southwest. 2. Dung beetles were sampled from three study sites in each of the six study areas using 2 × 10 grids of pitfall traps baited with dung (pig, elephant, cattle, and sheep) or carrion (chicken livers). 3. Canonical correspondence analysis (CCA) showed that distributions of dung beetle species between bait types deviated significantly from random associations. 4. Central Kalahari assemblages were more specialist than those at the mesic and arid extremes of the gradient. 5. Patterns of selection and specialisation to bait types differed between mesic northeast and arid southwest study areas. There were specialist faunas on carrion and more generalist faunas on ruminant herbivore dung (cattle and sheep) in each region. However, specialist species associated with elephant dung in the northeast were replaced by a more generalist fauna in the southwest with an opposite trend on pig dung. 6. Reduced species richness and high species turnover from the mesic northeast to the arid southwest is paralleled by a shift in patterns of food association that may reflect changes in the diversity of food types, particularly the absence of elephant dung from the southwest.     

Experimental evidence for the effects of dung beetle functional group richness and composition on ecosystem function in a tropical forest

Much of the literature on the relationship between species richness or functional group richness and measures of ecosystem function focuses on a restricted set of ecosystem function measures and taxonomic groups. Few such studies have been carried out under realistic levels of diversity in the field, particularly in high diversity ecosystems such as tropical forests. We used exclusion experiments to study the effects of dung beetle functional group richness and composition on two interlinked and functionally important ecological processes, dung removal and secondary seed dispersal, in evergreen tropical forest in Sabah, Malaysian Borneo. Overall, both dung and seed removal increased with dung beetle functional group richness. However, levels of ecosystem functioning were idiosyncratic depending on the identity of the functional groups present, indicating an important role for functional group composition. There was no evidence for interference or competition among functional groups. We found strong evidence for overyielding and transgressive overyielding, suggesting complementarity or facilitation among functional groups. Not all mixtures showed transgressive overyielding, so that complementarity was restricted to particular functional group combinations. Beetles in a single functional group (large nocturnal tunnellers) had a disproportionate influence on measures of ecosystem function: in their absence dung removal is reduced by approximately 75%. However, a full complement of functional groups is required to maximize ecosystem functioning. This study highlights the importance of both functional group identity and species composition in determining the ecosystem consequences of extinctions or altered patterns in the relative abundance of species.