Biomass of larval Scarabaeidae (Coleoptera) in relation to grazing pressures in temperate, sown pastures.
Abstract
Four years' data on the biomass of scarabaeid larvae in eighteen 1.2-ha pastures in New South Wales were obtained by a plough technique. The pastures were grazed continuously with approximately 8, 12 and 16 sheep/ha, using 2 breeds and 3 lambing times, in factorial combination. A highly significant quadratic relation was found to exist between total scarabaeid biomass (log scale) and 'grazing pressure'. This was defined as the number of Merino ewes per hectare multiplied by 1.15 if the lambing time was spring, and again by 1.15 if instead the sheep were Dorset Horn. These factors determined from the data for total scarabaeid biomass. The total biomass of scarabaeids peaked at a grazing pressure of 12.9, which was equivalent to approximately 12 breeding Merino ewes/ha, on pastures sown to Phalaris aquatica and Trifolium repens. However, over the range from 10 to 15 in grazing pressure there was little systematic variation in scarabaeid biomass. The dominant genera, Anoplognathus and Sericesthis, each showed significant quadratic relations to grazing pressure, but Antitrogus numbers were insufficient to exhibit any systematic effect. The clover content of the pastures, although affected by grazing pressures, appeared to have no significant effect on the biomass of larval scarabaeids.