No.78 June 2003 Notes from The diverse lizards of Oz the Australia has a great diversity of lizards – as many as 47 different species have Editor been found living in a single sand dune. Conditions which mammals find so harsh are apparently not such a disadvantage for reptiles. Next to birds, lizards are among the most commonly encountered Next to Antarctica, Australia is the have reptiles exploited an environment vertebrate animals in the driest continent on earth – 75 percent largely uninhabitable for other animals. savannas. Indeed, the diversity of of it is arid or semi-arid. The climate is lizards in the tropical savannas is erratic, with long, irregular dry and wet The great diversity of reptile species particularly rich, exploiting cycles determined by the effects of El may be due to the long-term stability, numerous habitats from Nino and La Nina. Successful animals and great size, of the Australian woodlands to sandstone must cope with unreliable rainfall and continent. Those animals which cope escarpments, rainforests and prolonged periods of shortages, but well with harsh conditions have had semi-arid zones, many endemic to take advantage of unpredictable times plenty of time to evolve into different just small areas. This Tropical of plenty. In addition, Australia’s soils species exploiting different ecological Topics looks at some of the more are also nutrient-poor with low niches. This diversity may even be widespread and common species. productivity, and fires are frequent. fostered by shortages, favouring large numbers of specialist species which This issue also looks at Energy efficiency is thus the key to have adapted to localised conditions crocodiles. Although not lizards, long-term survival. Mammals and birds over fewer, more widely distributed they are lizard-like in many generate their own heat from food, species which might have evolved in a respects and are important using up to 90 percent of their energy more benign environment. reptiles of the savanna intake for this purpose. Reptiles, waterways. Visitors to tropical however, tap into the abundant solar Reptiles have fared much better than Australia must always be aware – energy to fuel their activities. They are mammals and birds following the and beware – of these fascinating also much more water efficient (see arrival of Europeans in Australia. but potentially dangerous p. 2). When times are lean, since they Over 12 percent of mammals have animals. do not need to eat to maintain body become extinct and over 17 percent heat, reptiles can reduce their have declined, compared with just I would like to thank Russell Best, metabolism and go into a state of one possible reptile extinction. Queensland Parks and Wildlife suspended animation for prolonged Medium-sized mammals weighing Service, and Tony Griffiths, Key periods. between 35g and 5.5kg have been Centre for Tropical Wildlife worst affected. During droughts, Management, Northern Territory The combination of poor soils and dry larger mammals and birds can often University, for their help with this climate is believed to have led to the move to wetter areas. Smaller issue. evolution of plants with tough, thick, mammals, however, have probably chemical-laden leaves and relatively always lived a boom/bust existence – Contents: few plant-eaters. Instead, the those lucky enough to retreat to vegetation is broken down by termites, wetter refuges eventually able to Page 1: The diverse lizards of Oz which thrive in Australia, providing an recolonise areas where less fortunate Page 2: What makes lizards tick? abundant food source for reptiles. Just animals died out. Nowadays, these House guests; Frills in the fire as mangroves don’t need salt but have refuges attract cattle which compete Page 3: Crocodiles developed strategies for living where for the same resources. In addition, Pages 4&5: Lizards in the no other plants can rabbits have severely reduced savanna compete, so too ground cover and foxes and feral cats Page 6: Questions & answers are serious predators. Changed fire Facts and stats; Tourist Talk regimes also make life difficult for Page 7: Out and about many mammals and birds. Reptiles Page 8: Bookshelf seem more resilient to the same pressures. What makes lizards tick? Lizards are efficient creatures. Instead of consuming food to Geckos, legless lizards and skinks will readily drop their tails generate energy, most use solar power, basking in sunshine or when threatened, the wriggling appendage serving as a sleeping in a warm spot to power up their ‘batteries’ for the distraction while the owner makes its getaway. Fracture planes day’s (or night’s) activities. Some lizards, such as dragons, are between certain vertebrae at the top of the tail allow it to able to raise their ribs and angle their bodies to increase the detach easily when pulled apart by special muscles. This body surface exposed and can become darker to absorb more sacrificial offering is easily regrown. Tails of dragons and heat. This strategy, known as active thermoregulating, is not goannas can also break off, but do not do so as readily and an option for some lizards which live in closed forests. tend not to regrow. Instead, they thermoregulate passively, or ‘thermoconform’, their body temperature simply conforming to that of the air All dragons, goannas and Australian geckos lay eggs but around them. some skinks give birth to live young. Viviparity, as this is known, is more common in cool-climate reptiles, perhaps Lizards are also efficient users of water. Their dry scaly skin because the warmer temperatures inside the mother’s body reduces moisture loss, those living in the hottest areas lead to better development of the young. tending to have compact bodies to minimise loss and/or restricting most activities to hours of darkness. In addition, Most lizards are silent, but geckos chatter and squawk, some reptiles do not use water to flush nitrogenous wastes from the species making the characteristic and sometimes startling body as urine, like mammals do, but convert them to a form ‘gecko’ call which has given them their name. Legless lizards which can be dumped as solid dung. may make a high-pitched squeak and some skinks produce a soft squeak. House guests Frills in the fire Geckos are among the Dubious Fires are common in savanna woodlands so how do they most familiar of dtella affect the frilled lizards which live there? Researchers found tropical animals, that, on the whole, fires benefited these lizards, mainly by living in our houses, removing ground cover and allowing them a better view of scuttling around our ceilings, swarming around our outside potential prey. However, different types of fires have different lights to pounce on dazzled insects and conducting their effects. Fires occurring early in the dry season are less intense affairs behind our picture frames. and do not seem to threaten the frilled lizards, which avoid them by staying in tree canopies. Late dry season fires, on the Several species of geckos qualify as ‘house’ geckos, having other hand, are much more dangerous killing up to 30 percent adopted humans as co-habiters. The dubious dtella (Gehyra of the lizards. Many of those studied chose to leave their dubia) is found widely in Queensland and northern New treetop retreats and seek shelter in termite mounds – a South Wales. Varying in colour from pale pinkish to brown successful strategy which saved their lives. Many, however, with darker markings, it can also be found in the wild on trees stayed in the trees which was much more hazardous. and in rock crevices. Nonetheless, areas burnt by late dry season fires seem to Another species, the house gecko (Hemidactylus frenatus) is provide more food for frilled lizards. Generally, abundance of an import from Asia which has hitched a lift with travelling invertebrates in the lizards’ stomachs decreases – termites by humans. It is now found at the tip of Cape York Peninsula, in more than 40 percent – but there is an increase in numbers of urban areas like Cairns and in the Northern Territory where it ants, which seem more active and abundant in burnt areas. is spreading from Darwin to settlements along the road south Importantly, however, the lack of vegetation cover means that towards Alice Springs. It seems to be dependent on human the lizards can find more, and larger, prey. habitation. This gecko can change colour, becoming pale at night and dark during the day. Although similar in appearance When compared, frilled lizards from areas unburnt for many to the dubious dtella it can be distinguished by its slightly years were not in as good condition as those from regularly spiny tail. It also has a distinctive loud scolding call; native burnt areas; areas unburnt for prolonged periods tended to house geckos make only a soft chattering call. have low populations of frilled lizards. On the whole, areas which are burnt regularly in the early dry season are most The nocturnal lifestyle of geckos prevents them from basking likely to benefit these lizards by in the sun as most lizards do to raise their body temperatures. increasing food supplies but not Instead, they choose daytime retreats which are warmed by threatening the animals’ lives. the sun, particularly in the afternoon, so that they are full of Although late season fires seem energy by sunset. to provide more food, they also Medical researchers are intrigued by Competition for kill off such a large proportion of how a gecko is able to grow a new tail suitable spots can the lizards that the population is without the fluid retention and swelling be fierce, leading unlikely to be sustainable if (lymphoedema) frequently associated to fights between such fires are too frequent.