Species Richness and Competition
Worldwide there are about 4000 species of scarabaeine dung beetles. Local species richness is generally related to the species richness of large mammalian grazing animals, although cattle dung does support a rich dung beetle fauna around the world. The most competitive assemblages of dung beetles occur in tropical grasslands, where up to 120 species can be present in local areas; here, competition for the dung resource is high.
Intraspecific competition for dung occurs in a range of beetle species, expressed as a reduction in the number of eggs laid/female at high densities. There is also evidence for interspecific competition in which the presence of beetles of one species reduces egg production of a second species. In these instances the competition is frequently asymmetric, and the larger species has a greater effect on the smaller species than the other way round, particularly at high beetle densities. The competitive advantage of larger beetles is associated with preemptive dung burial, whereby they bury a greater proportion of dung in the first day.
Interspecific competition is avoided where there are differences in patterns of dung use and reproductive strategies. Species can be allocated into functional groups on the way they use dung and where it is buried under the pats. Competition is reduced also by the occurrence of aggregated spatial distributions between the discrete dung pats as a result of timing of optimal flight activity and of dung or soil preferences. Of the species present in a region, only some will have a preference for the niche represented by each dung pat, including the time and place at which it is dropped.
The arrival of farmers from Europe in the 19th century led to a major change in the Australian landscape, resulting from planting pastures and introducing domesticated grazing animals such as sheep and cattle. Native beetles, active only for restricted periods of the year, and occupying mainly heath and other undisturbed habitats, were unable to use effectively the large quantities of cattle dung in the newly created pasture habitats. Dung fauna in these pastures thus consisted of a high abundance of dung-breeding pest flies, but few dung beetles or predatory beetles. George Bornemissza of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) suggested introducing to Australia exotic scarabaeine dung beetles adapted to open pasture habitats and active mainly at the time of year native beetles were not, to correct this imbalance in pastures, to improve nutrient cycling, and to control nuisance flies breeding in the dung. A total of 46 species of scarabaeine dung beetles were introduced into Australia between 1967 and 1995, of which 26 species are established. The project has greatly increased the rate of dung recycling in Australia and reduced the population of at least one important dung-breeding nuisance pest, the Australian bushfly, Musca vetustissima.
See also the Following Articles
Coleoptera • Cultural Entomology • Mating Behaviors • Parental Care
Bornemissza, G. F. (1976). The Australian dung beetle project— 1965-1975. Australian Meat Research Committee Review No. 30, 1-30. Doube, B. M. (1990). A functional classification for analysis of the structure of dung beetle assemblages. Ecol. Entomol. 15, 371-383 Edwards, P. B., and Aschenborn, H. H. (1988). Male reproductive behaviour of the African ball-rolling dung beetle, Kheper nigroaeneus (Coleoptera: Scarabaeidae). Coleopterists Bull. 42, 17-27. Halffter, G., and Matthews, E. G. (1999). "The Natural History of Dung Beetles of the Subfamily Scarabaeinae." Reprint Medical Books, Palermo. Hanski, I., and Cambefort, Y. (eds.) (1991). "Dung Beetle Ecology."
Princeton University Press, Princeton, NJ. Ridsdill-Smith, T. J. (1991). Competition in dung insects. In "Insect Reproductive Behaviour" (W. J. Bailey and T. J. Ridsdill-Smith, eds.). Chapman & Hall, London. Waterhouse, D. F. (1974). The biological control of dung. Sci. Am. 230, 100-109.
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