Australia has few permanent rivers. Extensive manipulation of its fragile river systems for irrigation, combined with massive deforestation, has accelerated soil degradation and contributed to extensive salinisation and creeping desertification. The 'islands' of comparative fertility are also the preferred habitat of most Australian fauna, which must compete for these areas with the rapidly growing, highly urbanised human population. The number of big warm blooded carnivores at the top of the food chain is very small and those animals tend to be little. The biggest carnivores tend to be cold blooded, like lizards and crocodiles, which have lesser energy requirements.
Metabolisms tend to be slow to conserve energy use.
Diversity of species is extremely high with a correspondingly minutely adjusted ecosystem incorporating highly specialised characteristics and co-operative behaviours. Some interesting adaptations amongst plants include the fact that Australia possesses the largest variety of carnivorous plants in the world. It is thought that these plants supplement our notoriously nitrogen deficient soil by obtaining nitrogen from live prey. This can be done most efficiently by various species developing intimate relationships. Species which belong to an ecosystem which does not have such efficient nutrient recycling are rapidly selected against.