Indicators of Bio-Diversity

Dung Beetles and Pasture Health

Ancient Symbol

The ancient Egyptians noticed that the scarab beetle (also known as coprid or dung beetles) had the ability to roll large balls of dung. Having performed the near impossible task of moving giant blocks of stone themselves, the Egyptians concluded that the earth was being turned by a giant scarab beetle, so they made this amazing little creature a sacred symbol.

Understanding the Eco-Balance in a Red Meat Production System

In order to produce food it is critical that the eco-system of the production site is maintained in a balanced state. The removal, therefore, of foliage from the site at a rate that exceeds the natural replenishment rate, is a recipe for certain destruction of the environment and the long term sustainability of the production site.

The movement of large animals, tractors, implements etc on farms has several effects on the structure of the soil which in turn affects plant growth. These could be both negative or positive depending on the management thereof.

On the positive side, soil moved by walking animals buries seeds and promotes germination. Secondly, trampling of litter promotes its decomposition and recycling of nutrients. Thirdly, trampled material forms a mulch layer that assists in moisture conservation. This is important in a semi-arid region such as South Africa.

One of the most important negative factors that affect the eco-system is the effect of concentrated excreta by animals on the pasture. Apart from soil compaction, dung fouled plants are temporarily unacceptable to animals. If dung is not dispersed or decomposed rapidly, it kills the plants and it smothers or lowers the production of the plant for up to a year or more. Undecomposed dung therefore represents a bottleneck in the recycling of nutrients where only about 20% of faecal nitrogen is returned to the soil.

When dung beetles are active however, it is estimated that the beetles bury 90% of faecal nitrogen in the soil. Research has shown that higher plant yield and nutrient uptake is achieved due to dung beetle activity. An 11% higher crude protein and 57% higher dry matter production has been recorded near dung pads than away from them. For this reason, the preservation of the beetle population is critical. The mis-use of veterinary chemicals such as tick remedies, which have an adverse effect on the dung beetles, is strictly controlled for the preservation of the beetles and farmers are trained to manage these properly.

Healthy dung beetles follow grazing animals closely and within hours of defecation, the dung is disintegrated, removed from the surface and carried deep into the soil below. The warm dung is rolled into balls and used by the female beetle as a medium into which she lays her eggs. These burrows not only create a nutrient rich sponge below the soil surface which is capable of storing valuable rain water for the plants above, but also loosens and aerates the soil. Furthermore, ingested seeds also lead to improved dispersal of plants. Through this action it is estimated that a cow returns up to 95% of the nutrients consumed.

The ancient Egyptian scarab beetle therefore, is indeed still the 'sacred symbol' of a well balanced eco-system. From this is born our scientifically backed “Certified Natural” farm bio-monitoring audit system under an International Standards Organization system.

Aim

Producers of high-quality food using natural bio-friendly methods qualify for “Certified Natural” certification. Successful marketing is dependent on maintaining a quality product through Good Agricultural Practices, which ensure a healthy environment and sustainable development of natural rescources. Dung-burying beetles are excellent bio-indicators of the environmental status due to their specialist habitat associations, their sensitivity to change, and their key role as an integral part of pasture and soil ecology. This involves the removal of dung from the surface and the recycling of nutrients into the soil.

Healthy Pastures

Healthy pastures show high species richness and high abundance of dung-burying beetles. However, there are unique but natural regional, local, seasonal and short-term factors, which define or modify dung beetle activity on each farm.

  1. Local species richness, species composition and abundance of dung beetle assemblages are strongly influenced by regional climatic and altitudinal factors. Dung beetle assemblages tend to be more diverse both at lower altitude and in warmer, moister, north-eastern climates of South Africa.
  2. Local variation in soil and vegetation type is also influential. The species abundance composition of dung beetle assemblages differs widely between sandy and clay soils and also between shaded and unshaded vegetation types. Density of vegetative cover is also influential.
Local variation in soil and vegetation type is also influential
  1. Dung beetles show distinct seasonality in activity. Species richness and abundance are greatest during warm wet seasons and least so during cool, dry or warm, dry seasons. These factors are taken into account during the bio-monitoring process.
  2. Following the same principle, there is also some day-to-day variation in species abundance structure in fresh dung during the seasonal peak in activity. This is dependent on the incidence of appreciable rainfall. Thus, greatest species richness and abundance of beetles flying to fresh dung is observed during warm wet periods and least in warm dry or cool cloudy periods. In general, flight activity is limited when temperatures are around 20 oC or lower, irrespective of weather conditions.
A healthy pasture ensures sustainable healthy development of livestock farming

Unhealthy Pastures

Unhealthy pastures consistently show lower than expected species richness and abundance of dung-burying beetles. Such pastures may result from mismanagement practices, particularly overgrazing and over-application of poisons.

  1. Exceeding the recommended stocking rates leads to overgrazing, resulting in long-term reduction of surface cover. Loss of surface cover results in increased surface temperature, increased run-off, and more rapid evaporation of surface soil moisture, which may lead to vegetation changes more suited to warmer drier conditions. All of these factors influence dung beetle activity.
  2. Burning of healthy pastures also influences surface cover density in the short term. However, one study on highveld (1700 m) and middle veld (1300 m) grassland showed mostly minor differences in dung beetle species abundance patterns between burnt and unburnt pastures.
  3. Over-frequent use of pour-on acaricides (tickicides) leads to high frequency of lethal residues in dung. Residues of the least toxic synthetic pyrethroids and avermectins still remain lethal to dung beetles for around one week after treatment . Even under the recommended rate of dosage with avermectins, statistical modelling suggests that up to 25% of the dung beetle fauna could be lost over the period of one year. Thus, it would be better to apply pour-ons during drier periods when there is less dung beetle activity than during wetter periods.
  4. Planned pasture modifications may also result in much reduced dung beetle activity if these diverge widely from conditions in natural pastures. In one study, replacement of natural grassland by a dense mat of possibly fertilized Kikuyu grass resulted in a serious reduction of species richness and abundance of dung beetles in the KwaZulu-Natal midlands.
  5. Feed quality may also influence dung beetle activity. Bioassay studies show that breeding success of cattle dung beetles is reduced by low nitrogen, high fibre and low water content of the dung. The relative attractiveness of dung of differing qualities remains to be tested. However, it is likely that diet has at least some effect on the dung fauna through differences in chemical volatiles released by the dung to which dung beetles are attracted by their sense of smell.
  6. Some possible effects of serious reduction or even loss of the dung beetle fauna may be predicted by the past experiences of Australian cattle farmers. In Australia, cattle were introduced only in the eighteenth century. Dung beetles adapted to cattle dung were absent. By the 1960’s, there were several major problems including reductions in pasture area due to fouling by dung, reductions in nutrient recycling, and build up of large populations of dung-breeding fly pests.

Microhabitat Processes Maintaining Healthy Pastures

Research will be conducted into the microhabitat processes that are responsible for maintaining pasture health or modifying dung beetle activity. These processes are probably linked to factors that modify soil temperature and soil hardness. Soil temperature is influenced both by vegetative cover and soil moisture content. Soil hardness is influenced primarily by grain size and soil moisture content. Any changes that pertain to vegetative cover or to drainage, water retention and rate of evaporation, may influence dung beetle activity. Such changes can occur due to overgrazing, improvement of pastures, or ploughing. In the event of such past damage to natural grassland, dung beetles will be good indicators of the restoration of healthy pastures.

Monitoring of Dung Beetles Using Dung-baited Pitfall Traps

Rationale

Dung beetles are highly specialized to dung, soil and vegetation type. Changes in the natural system are reflected by changes in the dung fauna. Detection of changes, or their absence, is the rationale behind a trapping programme for monitoring dung beetle assemblages over time. This monitoring will provide an assessment of pasture health on selected farms affiliated with South African Natural Beef (Pty). The design of the trapping programme is according to the spatial and temporal factors that influence dung beetle occurrence.

Trapping Sites and Monitoring

Trapping sites on selected farms are monitored over a single 24 h period each month during the rainy season. Three trapping sites are selected in each soil and grassland type if this comprises 20% or greater of the grazing-land area on each farm. If there are major altitudinal differences greater than 400 m, trapping sites are selected in both lower and higher situations. Trapping sites are situated close to where cattle are grazing in situations that are characteristic of the overall grassland vegetation. A total of five traps are placed at least 10 m apart at each trapping site.

The Pitfall Trap and trapping procedure

The traps are simple in design and easy to use. They comprise a 2 Litre plastic bucket, two 30 cm galvanised wires to support the bait, and a 40 cm square of chiffon in which to wrap the 300 ml cattle dung bait. Each 24 h trapping occasion preferably commences on a warm day following rainfall greater than 15 mm. As dung beetle activity is maximal during warm wet weather, trapping under such conditions permits us to standardize the dung beetle catches on each trapping occasion. Traps are baited in the early morning and rebaited in the late afternoon to ensure that there is fresh dung to attract both day and dusk/night-flying beetles.

Dung beetle trap composing a plastic bucket with soapy water to immobalize the catch and two galvanized wires to support the cattle dung bait that is wrapped in thin cloth to exclude dung beetles but permit release of volatiles to which dung beetles are attracted by their sense of smell.

Processing the Catch

The catch is preserved in jars containing 70% alcohol and returned to the Department of Zoology and Entomology, University of Pretoria, where specialists identify the catch to species level and count the numbers of each species. This species abundance data is compared with baseline data characteristic for the region and also with data from previous trapping occasions. These comparisons enable us to assess whether or not changes in pasture health are occurring on monitored farms.

Collecting the catch and placing it into a preserving jar

Certification

Producers who require certification as “Natural” production sites must conform to certain health and environmental standards. Pasture health, stocking rates, farm management and the environmentally safe use of anti-parasitic drugs is assessed by scientists competent to do so.

This is done with a view to establishing the most environmentally friendly products that are least likely to affect the dung beetle and least likely to leave harmful chemical residues in the meat or the farms used to produce cattle and sheep. This program is available to any farmer who seeks to make his property eligible for the inclusion in the “Natural” program.

The catch is assessed and compared with the existing database for the climatic region. The database being assembled using multiple data sets from nature reserves, reserves and other transects is regarded as a scientifically defendable standard for “Natural” pasture and is used in the labelling of red meat products.

The system provides objective scientific evidence that is very difficult to manipulate, making the audit and certification of properties highly effective. This is the only combination of “Natural” meat production and biological monitoring of pastures and chemicals anywhere in the world.

The Natural Dung Fauna

Faunal Diversity

Dung attracts a wide range of different insects, particularly flies and beetles. Several groups of both dung-eating and predatory maggot-eating beetles are very abundant in large droppings such as those of cattle. However, perhaps the most visible of these groups are the dung-burying beetles of the subfamily Scarabaeinae. The evolutionary history of this subfamily stretches back many millions of years and is dominated by its specialization to feeding and breeding on dung. Most dung beetles are able to fly and thus move easily from older to younger pads, which they are able to detect by their sense of smell. The primary importance of their dung-burying habits results from their maintenance of pasture health both through natural manuring of the soil and removal of breeding sites or refuges for livestock pests.

Dung-burying beetles vary in size and habit. Some roll balls of dung, which are buries a distance from the dropping.

Four ball-rolling genera are illustrated.

 

Other bury dung at a series of different depths in vertical or slanting tunnels excavated from under the dropping.

Five tunneling genera are illustrated.

 
A very few endocoprid beetles no longer bury dung but spend their lives entirely within droppings. Some small kleptocorid dung beetles use dung buried by other larger dung beetles.

Nests

Nest architecture varies between species but follows common patterns. Both tunnelers and ball rollers bury dung at the ends of tunnels in the soil. Excavation is performed by using the front legs and some species use their shovel shaped heads to push soil out of the tunnel. Many tunneling species merely pack dung into the end of a tunnel or into the ends of tunnel branches. Similarly, a few ball-rolling species roll a dung ball away from the pad, lay an egg in the ball, then bury it in the soil. However, some tunneling and most ball rolling species model portions of dung into one or several balls within a chamber at the end of the tunnel. Most species lay a single egg in each dung ball or dung ovoid which are termed broods. However, a few species make multiple broods in the form of a mat or a sausage.

Life Cycle

Although the life cycles of different dung-burying beetles vary in detail, all share many common features. Within each brood, the larva hatches and grows by eating out the inside of the brood. The larva is quite different in appearance to the adult, therefore, after moulting three times it finally changes into the dormant pupal stage during which the body shape is reorganized into that of the adult. The new adult breaks through the wall of the brood in response to rainfall and high temperatures. It then feeds until it reaches maturity. However, it does not increase in size as all adult dung beetles are full- grown. Most species breed repeatedly and, therefore, bury dung throughout the warm rainy season. A few breed only once a year as the females tend the young whilst they pass through the larval stages and develop into new adults. Thus, the life cycles of different species last from only a few months up to an entire year.

Different species of dung beetles show different dung exploitation and nesting behaviour. The diagram illustrates the four major patterns of dung exploitation. Main variants in nesting behaviour are described in the text.

Natural Factors Influencing Dung Beetle Occurrence in South Africa

There are approximately 500 different species of dung-burying beetles in South Africa. These species show clear differences as to where they are found and when they are found. Their regional occurrence is influenced by climate type and their local occurrence by soil, vegetation and dung type. Although each local community comprises one or several abundant species, the others are present in lower numbers in a fairly steep descending order of abundance. The activity of these species is influenced by daily, seasonal and year-to-year differences in weather patterns. Despite these different influences, similar assemblages of dung beetles should occur on farms where regional and local conditions are similar whereas dissimilar assemblages will occur on farms where regional and local conditions are dissimilar.

Biogeographical Centres

Geographical centres of dung beetle distribution are influenced primarily by climate type. However, extensive areas of particular soil and vegetation types may also be important. For instance, in the winter rainfall region where shrubland dominates naturally-vegetated areas, or in the arid sandveld of the south-west Kalahari where deep sands dominate.

The numbers of species in local assemblages deline from the summer to the winter rainfall regions. The numbers shown are those for year round studies. Over a few days, one may expect to trap only about half of the species present locally.

Functional composition of local dung beetle assemblages also differs from the summer to the winter rainfall regions. Tunnelers are proportionally better represented in warm, summer rainfall regions, such as Pretoria (Pta) or Mkuzi Game Reserve. In cooler or drier regions, where conditions suitable for dung beetle activity are of shorter duration, ball rolling species are proportionally better represented, as in the winter rainfall region (Cape of Good Hope Nature Reserve and West cost sandveld) or the cool, high Drakensberk.

Regional Species Richness Patterns

The numbers of dung beetle species varies between cooler or warmer, and drier or wetter climatic regions. Both regional species richness and that of local species assemblages decline from north-east to south-west.

Map showing the numbers of dung beetle species in different climatic regions of South Africa. The warmer, moister regions to the east support greater numbers of species than the cooler, drier regions to the south-west. Cooler higher regions in the mid-summer rainfall region support fewer species than warmer, lower regions.

Maps showing the seven principal biogeographical centres of dung beetles distribution in South Africa. The outlined regions are the four degree squares of latitude and longitude which harboured greater than 40% of the species comprising each group.

 

 

 

 

 

For sake of clarity only distributional centres are outlined. However, in reality, these patters overlap with one another as they comprise both strongly and weakly-centred species. Thus, local communities will differ in composition according to the geographical position of each farm in relation to their principal dung beetle distribution centres.

Climatic Regions and Seasonal Changes

There are four major climatic regions in South Africa, which differ according to rainfall seasonality. Dung beetle activity is shown to follow seasonal patterns of rainfall in two of these regions and would be expected to do likewise in the other two regions for which beetle data is unavailable.

The Kalahari region is low in rainfall and therefore sensitive to overgrazing and adverse environmental management. It is therefore of uttermost importance to use known patterns of dung beetle activity to track the impact of farming activity on the environment.

 

In the south-western region of South Africa, rain falls primarily in the cool winter so that activity by endemic dung beetles is bimodal with peaks in activity during warm, wet periods in spring and autumn. Reasonable activity continues into early summer due to the occurrence of summer-active species which have expanded their ranges from the adjacent summer rainfall regions. Weather data is shown for Cape Town (CT). Dung beetle data is from natural shrubland on the west coast sandveld, 60 km north of Cape Town.
In the north-eastern region of South Africa, rainfall and temperature peaks coincide in mid-summer. Dung beetle activity is unimodal and closely tracks the weather patterns. Weather data is shown for Pretoria (Pta). Dung beetle data is from open woodland on deep sand 35 km north-east of Pretoria.
In the southern region of South Africa, rainfall shows bimodal peaks in spring and autumn as at Uitenhage (U.) With the spring peak more emphasized to the west. Dung beetle seasonality would be influenced by geographical overlap between winter and summer rainfall elements.
In the arid south -western part of the summer rainfall region, peaks in temperature and rainfall occur in late summer as at Fraserburg (Fr.). Dung beetle activity would also be expected to follow the rainfall peak as elsewhere.

Effect of Weather Patterns and Soil Type on Local Dung Beetle Activity

Dung beetle activity is strongly influenced by soil type and by both short-term and long-term weather effects. As dung beetles are essentially a tropical group, temperatures are sufficiently high for extensive dung beetle activity only in spring, summer and autumn in South Africa. During these warmer months of the year activity varies with the incidence of rainfall. Thus, during wet periods and wet years, dung beetle species richness, abundance and dung burial are greater than in dry periods and drought years. Hot, dry conditions are probably unsuitable for dung beetle activity because soil surface temperatures increase above the preferred level. At and above 45 o C, they become lethal. If conditions are unsuitable for activity, dung beetles remain dormant in the soil.

Dung beetle activity is greatest immediately after appreciable rainfall then declines if there is little or no further rainfall. This is illustrated by decline in the number of species recorded on each of 10 days following heavy rain in bushveld grassland on clay near Pretoria.
Dung burial activity increases during periods when there is high frequency of appreciable
rainfall and decreases when rainfall declines. Two cycles of increased rainfall and dung
burial are shown in bushveld grassland on clay over a period of two mid-summer months near Pretoria.
Over an entire year, seasonality in temperature, rainfall and dung beetle activity results in increased dung burial during the warm wet summer and decreased dung burial
in the cool, dry winter of the mid- summer rainfall region. Data is for bushveld grassland on clay near Pretoria.

Even in healthy grassland, seasonal dung removal varies with weather conditions over the short-term. Average minimum, average and average maximum dung removal is shown for an entire rainy season (mid-October - mid- April) on two soil types near Pretoria. Average minimum reflects the low point during dry periods and average maximum the high point during wet periods. The amount of dung removed within both 24 h and after 7 days is much greater on sand than on clay grassland Averages are shown for fresh, 24 h and 7 day old cattle pads. The photographs illustrate stages in dung removal.

The greater dung removal within the first 24 h on sand is related to the emphasis on different body sizes and habits on sand and clay. Sand is a softer soil type, and there is an emphasis on large, fast, deep-burying, dung beetle species. Clay is a harder soil type, and the emphasis is on smaller, slower, more shallow-burying species. Although more dung is buried on sand in the first 24 h, the amount of burial thereafter is similar on both soil types. The greater proportion of remnants on clay are nevertheless highly shredded by dung beetle activity

Local Spatial and Trophic (Food) Patterns in Dung Beetle Assemblages

The dung beetle community on the bushveld to the northeast of Pretoria is used to illustrate some local distributional differences due to soil, vegetation and dung types. The principles will remain true for elsewhere in the summer rainfall region even though the details may be expected to differ.

Many dung beetles show clear associations with particular soil or vegetation types. Therefore, species, and species abundance, composition varies between habitats. Similarity between the dung beetle faunas of softer (deep sand) and harder soils (clay) was mostly less than 50% on the bushveld near Pretoria. The dissimilarity between the faunas of shaded (thicket) and unshaded vegetation (grassland) was also fairly strong. The fauna of open woodland was mostly much closer to both grassland and thicket faunas.

Many dung beetle species show a bias to particular dung types based on dropping size, water, nitrogenous and fibre content. In agro-ecosystems, like the Pretoria bushveld, the main trophic (food) groups are biased towards omnivore (pig) or herbivore dung (cattle, horse). However, some species are known to specialize on the moist, low-fibre pads of ruminant herbivores (cattle), the large, fibrous droppings of non- ruminant herbivores (e.g. Horses, elephants), the small high-smelling droppings of omnivores (e.g. humans, baboons) or on the pellets dropped by many smaller herbivores.

Effect of Climate and Weather Patterns on Daily (Diel) Dung Beetle Activity

Dung beetles may be divided into species that fly only during darkness and those which fly only during daylight. The timing of daily peaks in flight activity varies according to altitudinal, weather, and seasonal effects on temperature. In hot, lowland regions, nocturnal dung beetles fly at both dusk and dawn. However, in cooler highland regions, nocturnal species fly primarily at, or soon after dusk. In hot, lowland regions, day flying species show a peak in flight activity early in the morning. This changes to a mid-to late morning peak at higher altitude. There is also sometimes another peak in flight activity in the afternoon. Under cooler extreme highland or late summer temperatures the peak in flight activity occurs at midday. Most day-flying species are only active under bright sunny conditions. Few day flying species will fly on overcast days.

Night flying species are unaffected by cloud cover but will be affected by the cooler dusk temperatures which follow an overcast or cloudy day.

Further Reading

The processes involved in shaping dung beetle distribution and pasture ecology have been hypothesized, outlined and illustrated using photographs and scientific data drawn from many different sources. For further explanation of the use of dung beetles as bioindicators, refer to:

Scarabaeine dung beetles as indicators of biodiversity, habitat transformation and livestock treatment effects in agro-ecosystems (Adrian L.V Davis 1 , Clarke H Scoltz 1 , Peter Dooley 2 , Naeem Bham 3 , & Ute Kryger 1 )

  1. Dept of Zooology & Entomology, University of Pretoria
  2. The Natural Products Group
  3. Novartis South Africa, Animal Health

Visit the University of Pretoria, Scarab Research Group website at www.geocities.com/scarabgroup to access background information on the professional personnel involved in both compiling this account of dung beetle ecology, and in processing the dung beetle data.

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