The radiation of some biotic groups are clearly consequences of the evolution of particular resources in abundance (eg parrots and honeyeaters), but others are probably largely historical (eg marsupials). The low productivity of native Australian ecosystems has favoured the occurrence of mutualistic relationships. It has also meant that spatial heterogeneity has great functional importance for spatial heterogeneity as small areas of higher productivity are crucial refuges and are sites of intense competition and predation. Great temporal variability in primary productivity has favoured invertebrates and ectothermic vertebrates. It has also resulted in high prevalence of fire and the evolution of a fire-adapted biota. Within the wet-dry tropics of Australia, the greatest diversity of plants and animals is located in the extensive, but structurally simple and somewhat unproductive, eucalypt forests and woodlands (savannas). The wetlands and wet forests, being more productive, have more vertebrate herbivores and larger vertebrates predators but shorter food chains. Social insects dominate in the savannas, having substantial impacts on all aspects of the functioning of the savannas. The Australian savanna biota is clearly a distinctive eucalypt woodland biota rather than an attenuated rainforest biota as in South America or a grassland biota as in Africa. -from Author
