Oral presentation- Plenary 12th International Mammalogical Congress

Comparative ecology of desert mammals (#2)

Professor Christopher D Dickman 1
  1. University of Sydney, Camperdown, New South Wales, Australia

Most of the world's deserts are relatively young, forming or expanding during the Miocene and becoming progressively more arid during the Pliocene-Pleistocene epochs. As conditions became more arid, mammal faunas adapted in situ or moved in from more mesic surrounding regions. Despite the phylogenetic diversity of founders in the different world deserts, the arid conditions have long been claimed to shape convergent similarities in the morphology, behaviour, ecology and physiology of the extant mammal faunas. Thus, bipedal locomotion, granivory and economy of water use characterize gerbils (Muridae) and jerboas (Dipodidae) in arid parts of Africa and Asia, kangaroo-rats (Heteromyidae) in North America, gerbil-mice (Cricetidae) in South America, and hopping-mice (Muridae) in arid Australia. Convergent similarities can be seen also in phylogenetically different rock-dwellers, burrowers and mammalian members of several trophic guilds. Yet, profound differences occur too. In this talk I will highlight ecological and behavioural differences that have been described recently in small mammals from different world deserts, and present detailed results on two groups—rodents and dasyurid marsupials—from long-term studies in Australia's most extreme arid region, the Simpson Desert. Australia's central deserts have been a graveyard for medium-sized and many small mammals over the last two centuries, and now are dominated, uniquely, by insectivores (dasyurids: 22 species) and omnivores (rodents: 15 species). Many dasyurid marsupials persist at low densities (< 1 ha-1), conserve energy and water by extensive use of torpor, have fixed breeding seasons, and appear to selectively hunt particular prey at different times depending on the prevailing conditions. Small dasyurids do not construct burrows, and instead make temporary use of the burrows of other desert dwellers. They adopt a mobile strategy that allows them to track shifts in key food resources across the desert landscape. Directed movements can exceed 10 km. Rodents, by contrast, show large population fluctuations, oscillating between prolonged periods when they are almost undetectable (<< 1 ha-1) to transient peaks when densities can exceed 100 ha-1. These 'boom' and 'bust' cycles are driven by heavy episodic rains or floods. Rodents show flexibility in their social structures, diets, and timing of reproduction; most can breed at any time when conditions permit. Unlike their counterparts in other world deserts, Australia's desert rodents display exceptional mobility; home ranges may exceed 10 ha, and short-term movements of 5-10 km are not uncommon. No species are known to cache seeds or other food materials. Despite the convergent similarity in appearance of many desert small mammals, ecological and behavioural differences between them clearly can be large. The boom and bust cycles that characterize many Australian species are driven by the larger and more frequent rainfall events that occur in Australian compared with other world deserts, while high mobility and behavioural flexibility reflect uncertainty in when these events will occur. The boom-bust dynamic carries inherent risks: refuge patches that are used during bust periods are often degraded for other (largely pastoral) uses, while boom periods provoke irruptions of introduced predators. Careful management will be needed to ensure the continuity of extant desert faunas.