Rolling in the deep

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By Risidra Mendis

They can be found in many parts of the country. But we hardly notice these tiny black creatures rolling in piles of faeces, a trait that you don’t often find in other animals. Strange as it may seem these creatures known as dung beetles play an important role in the ecosystem. 

A new study shows that dung beetles navigate via the Milky Way, the first known species to do so in the animal kingdom. The tiny insects can orient themselves to the bright stripe of light generated by our galaxy, and move in a line relative to it, according to recent experiments in South Africa.

Previous research in Sri Lanka by Head of the Department of Natural Resources (DNR), Professor in Conservation Biology, Faculty of Applied Sciences (FAS), Sabaragamuwa University, Prof. Enoka P. Kudavidanage has validated the dung beetle as a suitable indicator to detect environmental changes. 

Based on that study, dung beetles are identified as a commercially applicable economic indicator for environmental quality validation to assess an agricultural landscape’s healthiness. The Dung Beetle Project initiated by the Wildlife and Nature Protection Society (WNPS) in connection with the Sabaragamuwa University hopes to develop an environmental quality validation tool for the agricultural sector using dung beetles as a biological indicator.

The Dung Beetle Project which will take two years to complete will be supervised by Prof. Kudavidanage herself and by Dr. S.S.R.M.D.H.R. Wijesekara (Senior Lecturer, DNR FAS, Sabaragamuwa University), Dr. E.P. N. Udayakumara (Senior Lecturer, DNR FAS, Sabaragamuwa University), Deepachandi Lekamge (Lecturer, DNR FAS, Sabaragamuwa University), and Rumeshika Perera (Research Student BSc. (Special) in Environmental Sciences and Natural Resource Management and DNR FAS, Sabaragamuwa University).

“The world is undergoing heavy environmental degradation due to human activity, threatening the existence of all living beings including humans. Environmental degradation is identified under three categories; land and soil degradation, degradation of water resources, and atmospheric degradation. The main causes of environmental degradation include land pollution, water pollution, air pollution, and noise pollution caused by anthropogenic activities, overpopulation, land disturbances, landfill and deforestation among others,” WNPS officials said.

Dung beetles as bioindicators

Many consequences such as human health risk, loss of biodiversity, ozone layer depletion, losses in the tourism industry, and negative impacts on the economy have occurred due to this environmental degradation which is one of the greatest threats to all living beings, including humans. 

“Bioindicators include biological processes, species, or communities and are used to assess the quality of the environment and how it changes over time. Lichens, dragonflies, crustaceans, beetles, and butterflies are examples of bioindicators used for environmental quality assessment. Faecal matter produced by living organisms is digested and removed from the environment, mainly by several environmental decomposers, such as fungi (mushroom), bacteria (saprobe), and invertebrates (beetles, earthworms, millipedes, and termites),” WNPS  officials explained.

 They added that the dung beetle is one of the much-known decomposers involved in this cleaning task on behalf of all other living beings. “Dung removal is a much-needed ecosystem service that safeguards other organisms from dung dwelling parasites, keeps the soil substrate clean and disperses seeds.

“Their functional ability combined with the complex community structure that readily responds to environmental changes, and the cost-effectiveness of sampling makes them one of the top five biological indicators in the world to detect habitat disturbance. Their presence in the ecosystem can be attributed to the healthiness, disturbance, and other species’ richness,” WNPS officials said.

Services of the dung beetle

There are about 5,000 dung beetle species estimated on the earth. Dung beetles are classified into three groups according to how they utilise dung for feeding and laying eggs. Some dung beetles are functionally known as ‘Rollers’, where they remove dung from the original location in a ball that is rolled away. The other two groups are ‘Tunnellers’ (where they burrow through the dung pile at the original location) and ‘Dwellers’ (live in the dung pile; neither roll nor burrow). In the Sri Lankan context, 103 dung beetle species are recorded with 21 (20 per cent) endemic species, denoting eight tribes.

Dung beetles provide several ecosystem services, mainly through decomposing faeces during their dung removal process. They prevent the occurrence of ‘dung pollution’ as they accelerate the nutrient mineralisation processes, thereby helping nutrient circulation, aerating, and improving soil structure by burrowing tunnels and adding humus to the soil. 

The Australian Dung Beetle Project (1970 – 1980) is one of the best examples that expresses the value, service, and economic benefit of dung beetles to the world. Many studies have been conducted globally on dung beetles to identify them as a key indicator in different ecosystems, their functions, habitat, species differentiation, and their role in nature.

Dung beetles as economic indicators

“Dung beetle species diversity and abundance vary widely according to habitat characteristics. Due to environmental conditions and anthropogenic disturbances, dung beetle communities in a certain location can differ from another. The dung removal rate also can change simultaneously as the total biomass of beetles strongly correlates with their dung removal rates. They also depend on the different dung types of the host animal presence (carnivore, herbivore or omnivore), odour intensity, and nutrient availability in the area,” WNPS officials said.

 “This project is conducted to address biodiversity conservation, land conservation, and reforestation initiatives in the agricultural and corporate sectors. Dung beetles are commercially applicable economic indicators for environmental quality validation to assess an agricultural landscape’s healthiness.”

The dung beetle species was selected as an indicator species to assess the habitat quality of different land uses for the main research objective. Their presence and contribution to the dung removal activities in different land-use types will be observed with relatively different human interactions (disturbances) with multiple pathways.

 Objectives of the project

The objectives of the project are to identify dung beetle communities and their functional efficiency across four different land-use types (large forest (baseline), forest patches, home gardens, and plantations).

During the first step, a valuation gradient for environmental quality assessment will be established by selecting different land uses for the sampling of dung beetle diversity, community structure, and functions. The selected land use types will be of various degrees of human disturbance (large forest, fragmented forest patches, home gardens, and crop plantations under different land management practices). The large forest is selected as the baseline assuming a 100 per cent healthy ecosystem.

Data collected will be used to develop a correlation model where the habitat quality indicated by the dung beetle community and functional data will be related to environmental variables. 

The developed model will be used to analyse the environmental quality of selected land used and to differentiate the quality of plantations under different agricultural practices. This research expects to observe and identify the different dung beetle species abundance and richness changes in selected land uses in Sri Lanka. A model that can be used as a tool to measure the environmental quality of agricultural land will be developed. 

This model can be applied to compare the existing plantations that practice different agricultural techniques or to measure the progress of those converting to green/organic concepts.  The model will enable monitoring the green recovery of the plantations over time and the improvement of biodiversity and environmental quality. 

As an example, for a company or plantation that has been practising heavy chemical use, but now intends to shift to organic practices coupled with diversifying the habitat with the growth of forest patches, this model is a good initiative to start with monitoring the quality and the environmental health of the plantation from the beginning. The model will also provide data for reporting the plantations’ support for the environment and biodiversity conservation, especially for certification processes and marketing.

Other available dung beetle research

The research paper, Linking Biodiversity and Ecosystem Functioning of Dung Beetles in South and Southeast Asian Tropical Rainforests, by Yunnan China Lan Qie of  Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, and Janice Ser Huay Lee of the Department of Environmental Sciences, ETH Zurich, Switzerland say they investigated the impacts of habitat disturbance and the resulting changes in biodiversity on ecosystem function in South and Southeast Asian forests using dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) as a focal taxon. 

“Dung beetle sampling and dung burial experiments were conducted in intact, modified, and fragmented forest habitats in three different countries; Sri Lanka, Malaysia, and Singapore. Forest clearing and modification for human settlements and agricultural production is prevalent and accelerating throughout the tropics. Such changes in forest landscapes occur rapidly in South and Southeast Asia where a number of biodiversity hotspots are located. Ecological studies on conversion of forests to human land use areas in these regions have shown dramatic declines in populations and species richness across various taxa,” Prof. Kudavidanage said. 

The authors say resulting disruption of ecosystem functions and services are relatively less studied compared to losses in biodiversity and they investigate the linkages between biodiversity and ecosystem functions in South and Southeast Asian forests using dung beetles as a focal taxon.  

Benefits of dung burial

“Dung beetles are key bioindicators which are sensitive to tropical forest modification and fragmentation and provide a cost effective indicator group for tropical forest disturbances. Feeding and breeding activities of dung beetles involve dung burial through which dung beetles perform a series of ecosystem functions. Dung burial enhances soil fertility by making the critically important nitrogen available for plant uptake. Dung burial also results in soil aeration, secondary seed dispersal, and biological control of pests and parasites. 

All these functions are ecologically valued as important ecosystem services, and disruption of them through habitat disturbance will cascade into many trophic levels while causing significant economic loss to mankind. However, the understanding of the functional importance of dung beetles is primarily supported by data from pasture and grasslands which makes ecological and economical evaluation of their role in relation to tropical deforestation a critical need,” Prof. Kudavidanage explained. 

She said habitat modification and fragmentation are the most prominent types of landscape conversion leading to disturbance and previous studies have demonstrated that decreased species richness of dung beetles caused by habitat disturbance led to reduced dung burial rates and have highlighted the disproportional importance of large-bodied dung beetles in dung removal. 

“We hypothesise that increasing habitat modification and fragmentation will lower dung burial rates by dung beetles. Dung beetle diversity sampling and dung burial experiments were conducted in modified and fragmented forest habitats in three different countries; Sri Lanka, Malaysia, and Singapore. We conducted the study in and around Sinharaja, Kanneliya, and Kottawa-Kombala lowland tropical rainforests situated in the Southwestern region of Sri Lanka. Rates of dung removal, dung beetle richness, and abundance were sampled on transects in four habitat types (primary forests, selectively logged forests, tea plantations and home gardens) in each of the three above-mentioned forest sites,” Prof. Kudavidanage explained. 

She said the three modified habitats (selectively logged forests, tea plantations, and home gardens) were compared with the primary forest habitat as the control. “As observed during sampling, pristine forest and protected old, continuous and selectively logged forests contain more large mammals than the highly modified habitats, and therefore possibly support a greater variety of dung beetles which may explain the high rates of dung removal activity. Tunnellers consist of the major proportion of the dung beetle communities in the study sites of Sri Lanka, Singapore, and Malaysia,” Prof. Kudavidanage said.

For example, out of the 32 species recorded in Sri Lankan study sites, 26 species were tunnellers. “From the combined analysis of three studies conducted in South and Southeast Asia, it can be concluded that dung beetle communities and their dung removal function are negatively impacted by habitat modification and fragmentation regardless of the differences in countries and sites. The dung removal process was more influenced by the functional guild tunnellers which were predominant in the habitat modification analysis, while the abundance of dung beetle communities was more important for dung removal in the fragmentation analysis,” Prof. Kudavidanage explained.