The dung of carnivorous vertebrates is relatively poor-quality stuff. Carnivores assimilate their food with high efficiency (usually 80% or more is digested) and their feces retain only the least digestible components. In addition, carnivores are necessarily much less common than herbivores, and their dung is probably not sufficiently abundant to support a specialist detritivore fauna. What little research has been done suggests that decay is effected almost entirely by bacteria and fungi (Putman, 1983).
In contrast, herbivore feces still contain an abundance of organic matter. Autocoprophagy (reingesting one's own feces) is quite a widespread habit among small to medium-sized mammalian herbivores, being reported from rabbits and hares, rodents, marsupials and a primate (Hirakawa, 2001). Many species produce soft and hard feces, and it is the soft feces that are usually reingested (directly from the anus), being rich in vitamins and micro-bial protein. If prevented from reingestion, many animals exhibit symptoms of malnutrition and grow more slowly.
Herbivore dung is also sufficiently thickly spread in the environment to support its own characteristic fauna, consisting of many occasional visitors but with several specific dung-feeders. Dung removal varies both seasonally and spatially. In tropical and in warm temperate regions most activity occurs during summer rainfall, whereas in Mediterranean-type climates dung removal is highest during spring after the winter rainfall and again in mid-summer when temperatures are high (Davis, 1996). Dung removal also occurs at greater rates in unshaded situations and is faster on sand than on harder, more compacted clay soils (Davis, 1996). A wide range of animals are involved, including earthworms, termites and, in particular, beetles.
A good example of the predominant role of beetles is provided by elephant dung. Two main patterns of decay can be recognized, related to the wet and dry seasons. During the rains, within a few minutes of dung deposition the area is alive with beetles. The adult dung beetles feed on the dung but they also bury large quantities along with their eggs to provide food for the developing larvae. For example, the large African dung beetle, Heliocopris dilloni, carves a lump out of fresh dung and rolls this away for burying several meters from the original dung pile. Each beetle buries sufficient dung for several eggs. Once underground, a small quantity of dung is shaped into a cup, and lined with soil; a single egg is laid and then more dung is added to produce a sphere that is almost entirely covered with a thin layer of soil. A small area at the top of the ball, close to the location of the egg, is left clear of soil, possibly to facilitate gas exchange. After hatching, the larva feeds by a rotating action in the dung ball, excavating a hollow, and, incidentally, feeding on its own feces as well as the elephant's (Figure 11.15). When all the food supplied by its parents is used up, the larva covers the inside of its cell with a paste of its own feces, and pupates.
The full range of tropical dung beetles in the family Scarabeidae vary in size from a few millimeters in length up to the 6 cm long Heliocopris. Not all remove dung and bury it at a distance from the dung pile. Some excavate their nests at various depths immediately below the pile, while others build nest chambers within the dung pile itself. Beetles in other families do not construct chambers but simply lay their eggs in the dung, and their larvae feed and grow within the dung mass until fully developed, when they move away to pupate in the soil. The beetles associated with elephant dung in the wet season may remove 100% of the dung pile. Any left may be processed by other detritivores such as flies and termites, as well as by decomposers.
Dung that is deposited in the dry season is colonized by relatively few beetles (adults emerge only in the rains). Some micro-bial activity is evident but this soon declines as the feces dry out. Rewetting during the rains stimulates more microbial activity but beetles do not exploit old dung. In fact a dung pile deposited in the dry season may persist for longer than 2 years, compared with 24 h or less for one deposited during the rains.
Bovine dung has provided an extraordinary and economically very important problem in Australia. During the past two centuries the cow population increased from just seven individuals (brought over by the first English colonists in 1788) to 30 million or so. These produce some 300 million dung pats per day, covering as much as 6 million acres per year with dung. Deposition of bovine dung poses no particular problem elsewhere in the world, where bovines have existed for millions of years and have an associated fauna that exploits the fecal resources. However, the largest herbivorous animals in Australia, until European colonization, were marsupials such as kangaroos. The native detritivores that deal with the dry, fibrous dung pellets that these leave cannot cope with cow dung, and the loss of pasture under dung has imposed a huge economic burden on Australian agriculture. The decision was therefore made in 1963 to establish in Australia beetles of African origin, able to dispose of bovine dung in the most important places and under the most prevalent conditions where cattle are raised (Waterhouse, 1974); more than 20 species have been introduced (Doube et al., 1991).
carnivore dung is attacked mainly by bacteria and fungi
'autocoprophagy' among mammalian herbivores herbivore dung supports its own characteristic detritivores a diversity of dung beetles
Australian cow dung poses a problem
Adding to the problem, Australia is plagued by native bushflies (Musca vetustissima) and buffalo flies (Haematobia irritans exigua) that deposit eggs on dung pats. The larvae fail to survive in dung that has been buried by beetles, and the presence of beetles has been shown to be effective at reducing fly abundance (Tyndale-Biscoe & Vogt, 1996). Success depends on dung being buried within about 6 days of production, the time it takes for the fly egg (laid on fresh dung) to hatch and develop to the pupal stage. Edwards and Aschenborn (1987) surveyed the nesting behavior in southern Africa of 12 species of dung beetles in the genus Onitis. They concluded that O. uncinatus was a prime candidate for introduction to Australia for fly-control purposes, since substantial amounts of dung were buried on the first night after pad colonization. The least suitable species, O. viridualus, spent several days constructing a tunnel and did not commence burying until 6-9 days had elapsed.
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