ABSTRACT. The dung colonization and dung burial behaviour of twelve crepuscular/nocturnal tunnelling (paracoprid) species of beetles were examined in order to identify mechanisms which might facilitate resource (dung) partitioning. The species were selected from a diverse assemblage of dung beetles, the members of which coexist in the sandy‐soil regions of Natal, South Africa. The pattern of dung colonization in relation to dung age was examined in the field using baited pitfall traps. Some species, e.g. Onitis deceptor Peringuey, Catharsius tricornutus De Geer and Copris elphenor Klug, showed a marked preference for fresh dung (1–2 days old) whereas other species, e.g. O. viridulus Boheman and Copris fallaciosus Gillet, preferred older dung (3–7 days old). Two distinct patterns of dung burial were recognized. In the Coprini, dung burial was complete within 24–48h of pad colonization, and the level of dung burial was similar in the laboratory and in the field. In the Onitini, dung burial occurred progressively over a 12‐day period, although the timing of initiation of dung burial varied between species: in O. deceptor nearly all individuals had begun burial within 2 days of pad colonization, whereas only 20% of O. viridulus had commenced dung burial by that time. However, nearly all O. viridulus had buried substantial quantities of dung by day 12. The mass of dung buried per pair by the larger coprine beetles (100–300 g) and onitine beetles (400–1000 g) suggests that there is potential for inter‐ and intraspecific competition, even in pads colonized by relatively few beetles. The colonization and use of dung of different ages are discussed as means of resource partitioning in relation to the relative abilities of species to compete for dung.
The effects of larval crowding on development, survival and size of the African buffalo fly, Haematobia thirouxi potans (Bezzi), were examined in small (10 or 20 g) and 1000 g masses of cattle dung in the laboratory at 25°C. Dung was infested with fly eggs at densities which ranged from 0.05 to 32.0 eggs per g dung; in most cases 90–100% of eggs hatched. The duration of larval development in 10 g dung masses was extended by larval crowding at densities above 0.8 eggs per g dung and the development period with 32 eggs per g dung (11 days) was double that observed in uncrowded dung masses. Both size and survival decreased with increasing larval density, but stunting was observed at lower densities than those which reduced survival and so size was the more sensitive index of the adequacy of the larval environment. The effects of larval crowding became evident at lower larval densities in the 1000 g dung masses than in the 10 g dung masses. There was a minimum size below which third instar larvae failed to pupariate. The probability of survival was related to pupal size and a high proportion of the smaller individuals failed to eclose. Résumé Effets de la competition intraspécifique sur le développement des larves, la taille des pupes et la survie d'Haematobia thirouxi potans Les effets du surpeuplement larvaire sur le développement, la survie et la taille d'Haematobia thirouxi potans, ont été examinés sur de petites quantités de bouse (10 et 20 g) et de plus importantes (1000 g), au laboratoire à 25°C. Les bouses étaient contaminées avec des oeufs de la mouche à des densités de 0,05 à 32 oeufs par gramme de bouse. Dans la plupart des cas le taux d'éclosion était de 90–100%. La durée du développement larvaire dans 10 g de bouse a été prolongée pour les densités supérieures a 0,8 oeuf per g, et la durée développement pour 32 oeufs per g (11 jours) était le double de celle obtenue grand il n'y avait pas surpeuplement. La taille et la survie diminuent toutes les deux avec la densité larvaire, mais la miniaturisation était observée à des densités où la survie n'était pas modifiée; ainsi la taille est un indice plus sensible de l'adéquation de l'habitat larvaire. Les effets du surpeuplement larvaires deviennent clairs à des densités plus faibles avec 1000 g de la bouse qu'avec 10 g. Il y a eu une taille minimale endessous de laquelle les larves étaient incapables de former une pupe. La probabilité d'éclosion était liée à la taille de la pupe, et une plus forte proportion de petits individus ne sont pas parvenu à éclore.
The effect of dung burial by the African dung beetle Catharsius tricornutus De Geer on the survival and size of the dung-breeding African fly Haematobia thirouxi potans (Bezzi) was examined in the laboratory at 25°C using 1-litre pads of cattle dung. The experiment included a set of dung pads which were exposed to infrared radiation for 12 h per day to mimic the heating effect of solar radiation. C. tricornutus is a large (1–2-g live weight) dung beetle, and moderate numbers can completely bury dung pads within 24 h of pad colonization. Dung burial was proportional to the number of pairs present (range 0–8 pairs per pad), but the level of burial was reduced in the presence of infrared radiation. Dung pads lost moisture with time, and the rate of desiccation of unburied dung increased with the amount of dung burial and under infrared radiation. Mortality in the immature stages of H. t. potans increased with increasing levels of dung burial and with exposure of pads to infrared radiation. The timing of addition of dung beetles (i.e. before or after egg hatch) did not affect fly survival. At moderate levels of dung burial, fly larvae were killed directly by beetle activity and at high levels of dung burial, fly larvae also perished due to an unfavourable physical environment associated primarily with moisture stress. Infrared radiation killed immature flies and increased the level of moisture stress. There was a low level of survival in dung buried by the beetles under these unnatural laboratory conditions. Stunting of surviving flies was associated with reduced levels of moisture in the core of the unburied dung and was observed when the level of dung burial was >60% in ambient conditions and >40% under infrared radiation.
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