(1) A simulation model of grazing mechanics in ruminants shows that, due to the allometric relations of bite size and metabolic requirements to body size, small animals are able to subsist on shorter swards than large animals.\ud \ud (2) The density of nutrients in the grazed horizon of the modelled swards markedly affected the ability of animals of a given body size to satisfy their energy requirements.\ud \ud (3) By extension, the allometric relationships would be expected to apply in selective grazing and browsing species in their choice of food items of different size and nutrient content.\ud \ud (4) The results support the argument that sexual segregation and habitat choice of dimorphic species is an effect of scramble competition for limited resources, the males thus being excluded from mutually preferred swards.\ud \ud (5) The model provides an explanation for two interspecific phenomena amongst grazers: grazing succession and grazing facilitation

This article provides a context to, attempts an explanation for, and proposes a response to the recent demonstration of rapid and severe decline of the native mammal fauna of Kakadu National Park. This decline is consistent with, but might be more accentuated than, declines reported elsewhere in northern Australia; however, such a comparison is constrained by the sparse information base across this region. Disconcertingly, the decline has similarities with the earlier phase of mammal extinctions that occurred elsewhere in Australia. We considered four proximate factors (individually or interactively) that might be driving the observed decline: habitat change, predation (by feral cats), poisoning (by invading cane toads), and novel disease. No single factor readily explains the current decline. The current rapid decline of mammals in Kakadu National Park and northern Australia suggests that the fate of biodiversity globally might be even bleaker than evident in recent reviews, and that the establishment of conservation reserves alone is insufficient to maintain biodiversity. This latter conclusion is not new; but the results reported here further stress the need to manage reserves far more intensively, purposefully, and effectively, and to audit regularly their biodiversity conservation performance.

The process of weaning is related to a critical or threshold body weight attained by offspring among large‐bodied mammals; the anthropoid primates, ungulates and pinnipeds. While weaning weight was allometrically related to maternal weight in interspecific comparisons, it was isometrically related to neonatal weight. When a neonate had grown to four times its birth weight, it was weaned. Differences between taxonomic groups were found only among the fasting phocids, where weanlings attained a lower, but proportional, weight. The duration of lactation was only weakly allometrically related to maternal or neonatal weight, and varied between individuals intraspecifically as a function of maternal condition. The time to weaning appears to be ecologically sensitive rather than to reflect interspecific life‐history variation, in that, irrespective of the time to weaning, similar proportional weights appear to be attained. Interspecific similarities in threshold weaning weights are suggested to result from constraints on maternal abilities to meet energetic requirements of offspring through lactation after infants attain a threshold weight.