Seasonality in the dung beetle community in a Brazilian tropical dry forest: Do small changes make a difference?

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.

Early successional dynamics of ground beetles (Coleoptera, Carabidae) in the tropical dry forest ecosystem in Colombia

Little is known about the successional dynamics of insects in the highly threatened tropical dry forest (TDF) ecosystem. For the first time, we studied the response of carabid beetles to vegetal succession and seasonality in this ecosystem in Colombia. Carabid beetles were collected from three TDF habitat types in two regions in Colombia: initial successional state (pasture), early succession, and intermediate succession (forest). The surveys were performed monthly for 13 months in one of the regions (Armero) and during two months, one in the dry and one in the wet season, in the other region (Cambao). A set of environmental variables were recorded per month at each site. Twenty-four carabid beetle species were collected during the study. Calosoma alternans and Megacephala affinis were the most abundant species, while most species were of low abundance. Forest and pasture beetle assemblages were distinct, while the early succession assemblage overlapped with these assemblages. Canopy cover, litter depth, and soil and air temperatures were important in structuring the assemblages. Even though seasonality did not affect the carabid beetle assemblage, individual species responded positively to the wet season. It is shown that early successional areas in TDF could potentially act as habitat corridors for species to recolonize forest areas, since these successional areas host a number of species that inhabit forests and pastures. Climatic variation, like the El Niño episode during this study, appears to affect the carabid beetle assemblage negatively, exasperating concerns of this already threatened tropical ecosystem.

The Attraction of Amazonian Dung Beetles (Coleoptera: Scarabaeidae: Scarabaeinae) to the Feces of Omnivorous Mammals Is Dependent on Their Diet: Implications for Ecological Monitoring

The immense sampling effort used in ecological research on dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) has required large amounts of human feces to conduct experiments in the field. Thus, the amount of human feces available can be an important limiting factor for research. Therefore, dung from large omnivorous mammals, such as pig, has been used to reduce this limitation. Here, we evaluated how the type of diet can influence the attractiveness of omnivorous-mammal feces to Amazonian dung beetles. We sampled dung beetles in 10 fragments of Amazon rainforest in July 2018 (dry season) and March 2019 (rainy season), using pitfall traps baited with swill pig dung (household waste-based diet), grain pig dung (maize+soybean-based diet), and human feces (control) in Juína, Mato Grosso, Brazil. In all, 2,080 individuals from 51 species of dung beetles were collected. Between the pig dung evaluated, higher total abundance and species richness was captured with grain pig dung. However, the species composition and community structure were similar between pig dung types. Additionally, grain pig dung captured total species richness, species composition, and structure similar to that for human feces. Thus, although grain pig dung did not sample total abundance similar to human feces, this type of dung can be efficient for an accurate survey of the total species richness, species composition, and structure of dung beetles in the Amazon rainforest.

Macroevolution and shifts in the feeding biology of the New World scarab beetle tribe Phanaeini (Coleoptera: Scarabaeidae: Scarabaeinae)

The New World scarab beetle tribe Phanaeini contains coprophagous, necrophagous, mycetophagous and suspected myrmecophilous species. We analyse the largest tribal molecular dataset assembled, incorporating, for the first time, the enigmatic monobasic genus Megatharsis, the thalassinus group of the subgenus Coprophanaeus (Metallophanaeus), and the subgenus Dendropaemon (Eurypodea) (formerly Tetramereia), unveiling their macroevolutionary and biogeographical history in light of Cenozoic abiotic changes and inferring shifts in feeding biology through time. We recover the contentious genus Gromphas outside an otherwise monophyletic Phanaeini. We infer Megatharsis in a clade containing the apparent myrmecophilous genus Dendropaemon, within the Coprophanaeus clade, and demonstrate that the subgenus Coprophanaeus (Metallophanaeus) is polyphyletic, whilst species groups within the subgenus Coprophanaeus (Coprophanaeus) are monophyletic. Our divergence time analyses and ancestral range estimation indicate an eastern South American origin for Phanaeini in the early Eocene, with subsequent colonization of Central America and the Nearctic during the Oligocene, long before a Panamanian land bridge. A shift to necrophagy in Coprophanaeus is possibly linked to increasing Neotropical small vertebrate diversity since the Eocene and, astonishingly, myrmecophily evolved from necrophagy 35 Mya. These drastic shifts in lifestyle are not concordant with variations in diversification rates and appear unlinked to Quaternary extinction of large mammals.

Can taxonomic and functional metrics explain variation in the ecological uniqueness of ecologically-associated animal groups in a modified rainforest?

The conservation of biodiversity requires adequate information about species and ecosystem attributes. The local contribution to β-diversity (LCBD) is a community composition-based metric of ecological uniqueness of sites. Here, we tested the capability of taxonomic and functional attributes of biological communities to explain variation in LCBD at a large spatial extent. We approached this idea using data on dung beetles and mammals (medium-to-large, small and volant) recorded across the Atlantic Forest of South America due to their millennial-scale evolutionary relationship (food providers and consumers). We related LCBD values to both taxonomic and functional metrics via beta regression. Our results revealed that taxonomic and functional features of assemblages can be used to predict variation in ecological uniqueness (LCBD). High LCBD values were associated with low species and functional richness for all animal groups. For dung beetles, high LCBD values were associated with low values of all functional metrics. For mammalian groups high ecological uniqueness was associated with low abundance, low Rao's quadratic entropy, as well as high functional divergence, functional evenness, functional originality, and either low or high functional specialization. This implies that variation in ecological uniqueness can be explained by functional features at large spatial extents, although the type of functional metrics' response of assemblages may be animal group specific. The potential of the LCBD metric to inform about both taxonomic and functional changes at large scales makes its use in conservation planning a highly promising approach.

Attractiveness of Different Food Resources to Dung Beetles (Coleoptera: Scarabaeidae) of a Dry Tropical Area

Excrement scarcity is one of the main historical factors leading dung beetles to adapt to other food resources. In the Caatinga, a seasonally tropical dry forest, harsh environmental conditions seem to restrict the availability of food resources. In this scenario, the aim of our study was to experimentally investigate the attractiveness of different potential food resources to these insects in the Caatinga. Field samplings were performed, and we tested five resources in pitfall baited traps: excrement, carrion, fruits of two species of columnar cacti, and seeds of one species of Euphorbiaceae (Jatropha mollissima (Pohl)). In a controlled setting, we tested dietary preferences of Deltochilum verruciferum Felsche by offering one or two resources simultaneously. In the field experiments, 297 dung beetles (9 species) were recovered from the traps, and D. verruciferum was the most abundant species. Carrion and excrement were the most attractive resources. Controlled dietary preference tests with D. verruciferum evidenced that these beetles used all tested food resources, excrement and carrion most pronouncedly. Our findings support copro-necrophagy as the main feeding habit of D. verruciferum, but also suggest that alternative resources might be utilized if preferred resources are scarce.

How Does Dung Beetle (Coleoptera: Scarabaeidae) Diversity Vary Along a Rainy Season in a Tropical Dry Forest?

Dung beetle community dynamics are determined by regional rainfall patterns. However, little is known about the temporal dynamics of these communities in tropical dry forests (TDFs). This study was designed to test the following predictions: 1) Peak diversity of dung beetle species occurs early in the wet season, with a decrease in diversity (α and β) and abundance throughout the season; 2) Nestedness is the primary process determining β-diversity, with species sampled in the middle and the end of the wet season representing subsets of the early wet season community. Dung beetles were collected in a TDF in the northern Minas Gerais state, Brazil over three sampling events (December 2009, February and April 2010). We sampled 2,018 dung beetles belonging to 39 species and distributed among 15 genera. Scarabaeinae α-diversity and abundance were highest in December and equivalent between February and April, while β-diversity among plots increased along the wet season. The importance of nestedness and species turnover varies between pairs of sample periods as the main process of temporal β-diversity. Most species collected in the middle and end of the wet season were found in greater abundance in early wet season. Thus, the dung beetle community becomes more homogeneous at the beginning of the wet season, and as the season advances, higher resource scarcity limits population size, which likely results in a smaller foraging range, increasing β-diversity. Our results demonstrate high synchronism between the dung beetle life cycle and seasonality of environmental conditions throughout the wet season in a TDF, where the onset of rains determines adult emergence for most species.