The increasing aridity of the Australian continent over the past 20 million years has favoured organisms that could adapt to dry conditions. Marsupials have developed a variety of behavioural, physiological and morphological adaptations to survive in these arid conditions with little or no food and free water for extended periods of time.
Marsupials living in Australia’s hot arid environment must deal with exposure to extreme conditions such as high temperatures, solar radiation and limited food and water supply. More than 50% of the world’s marsupial species occur only in Australia (Steffen et al 2009), which indicates their ability to adapt to Australian conditions.
This essay will provide specific examples of the way Australian marsupials species have adapted to the arid Australian environment.
Marsupials have developed a variety of physiological adaptations to cope with arid Australian environments. Several examples of physiological adaptations are described below.
Torpor is a short-term state characterised by a reduction in the metabolic rate (MR) including a lower than normal body temperature (Tb) and heart and respiratory rate (Solomon et al, 2011).
Some Australian marsupials have evolved to utilise torpor as an effective survival strategy by reducing water loss and energy expenditure in the harsh arid zones in Australia where food and water are often in short supply (Geiser, 2004).
According to Geiser (2004), Dasyurids are one of the most effective small arid zone mammals due to their effective use of torpor, which is used to adapt to strong variations in food and water availability. As mentioned by Geiser (2004), Dasyurids utilise torpor during the night or early morning and utilise the sun’s warmth to rewarm from torpor, minimising energy expenditure.
Another species that utilises torpor to adapt to the arid zones in Australian is the short beaked echidna (Tachyglossus aculeatus), which enters extended periods of torpor according to Geiser (2004).
Reproduction is the process by which new individuals are produced (Solomon et al, 2011). Some Australian marsupials utilise reproductive adaptations to assist with survival in an arid environment.
Marsupials have an ability to survive in arid zones of low fertile soils and limited water and still reproduce through using a lengthy and complex lactation process (Tyndale-Biscoe, 2001).
Tyndale-Biscoe (2001) compares the long nosed bandicoot (Perameles nasuta) and the wild rabbit both of which have similar weights and litter sizes. However the lactation period in the bandicoot is almost three times longer than the rabbit and the gestation is double that of the rabbit. The bandicoot’s ability to reduce the gestation period and have a greater emphasis on lactation allows the bandicoot to be more responsive to adverse environmental conditions (Tyndale-Biscoe, 2001).
Another successful reproductive adaptation by marsupials is found in the desert dwelling kangaroo (Dipodomys merriami) which reduce their energy expenditure during pregnancy by giving birth to their young at an early development stage as discussed by Barker (1982) and Greenslade (1982).
During periods of limited food and water supply the female red kangaroos have been known to reduce their sexual activity and in extreme drought conditions may even go through a period of sexual inactivity as discussed by Brown (1974)
Behavioural adaptations are another important method of coping with limited water supply and high temperatures. Behavioural adaptations can be as effective in arid environments as physiological adaptations as noted by King (2008) and Bradshaw (2008).
The behavioural mechanism of heat avoidance by marsupials using burrows and caves for shelter assists with water...