Shrinking forests - what lizards can tell us about fragmented habitats November 1998

Tropical forests are the Earth’s most known as ‘edge effects’. As a block of valid conclusions regarding individual biologically diverse ecosystems. To forest becomes fragmented, there is an , you need large sample sizes. properly manage these unique areas, it incease in the amount which is edge. is important to understand the effects The scale that is investigated is very that reduced size and fragmentation of Edge effects are numerous and include different when looking at lizards the forests have on their inhabitants. It factors such as increased sunlight compared to mammals or birds. This is seems inevitable that small ‘islands’ of reaching the forest floor with associated because lizards are usually much rainforest will become the last refuges drying effects. Temperatures are smaller than birds and mammals, they of many rainforest species. These consequently hotter and more variable, do not move such large distances, and ‘islands’ or fragments may become the and humidity is lowered. Increased have smaller home ranges. In terms of ‘seeds’ from which to re-establish wind shear results in greater numbers , this means that extensive forests in the future. of fallen trees which further opens up the size of a forest fragment which can the canopy. The changed environmental hold a healthy population of is Why study fragments? conditions cause changes to sensitive likely to be different to that which can insect populations, and predatory hold a healthy population of either Studying the effect of fragmentation is behaviour by birds increases due to the birds or mammals. important because small isolated more open canopy. These are just some populations of and plants tend of the direct effects of increasing the Studies of the effects of fragmentation to decline in genetic diversity. This is a amount of edge. on reptiles are rare, but since they are problem as it can reduce their ability to known to adapt quickly to respond to changing environmental Why use lizards to study forest environmental change, especially in factors or to new diseases or parasites. fragmentation? ‘island’ systems, they are an ideal Another effect of fragmentation is the candidate for studying changes to shape changes caused to the physical Most previous studies have focused on or size. The two research stories environment. Plants and animals are birds and mammals, and their described here are about forest more likely to be exposed to what are responses at the community rather than which are abundant in the wet tropics individual level. To make statistically and easy to capture. Therefore, it has been possible to have good sample sizes Researchers, which are suitable for individual Joanna Sumner studies. and Craig Moritz, find Skinks are a family of lizards widely skinks by rolling distributed across Australia. They have logs and catching evolved into many species in the Australian desert and Australia them by hand outranks other countries in terms of the number of species. Despite this fact the biology of skinks is poorly understood, and very few Australians are even aware of their existence. This is probably due to the fact that they are, for the most part, small, cryptic and often overlooked in favour of larger, more obvious animals. Researching skinks in rainforest Hot and cold running skinks fragments There are two major strategies Simon Cook is a PhD student who is developed by skinks to deal with studying at James Cook University in living in a cool rainforest environment. lightbulb Townsville. The purpose of his research Skinks in the rainforest are either is to determine the diversity of skink ‘heliotherms’ or ‘thigmatherms’. leaf litter 30cm species living in tropical rainforest and Heliotherms actively seek sunny spots 180cm the difficulties they might have faced in to warm their bodies. In the rainforest the long evolutionary path needed to the opportunity for basking in sunlight evolve from desert skinks to rainforest is limited by the closed canopy of the 40cm skinks. Simon’s studies are forest, therefore most of the heliotherm concentrating on the importance of species are limited to areas such as Figure 1 The thermal gradient used to determine temperature. Lizards rely on gaining recent tree falls, where sunlight can preferred temperatures of different skink species in the heat from the environment to perform reach the ground. Thigmatherms don’t lab. The tank sits in a cold room at a constant normal bodily functions such as need to seek sunny positions to warm temperature of 16 oC digestion of food and reproduction, and their bodies, they are able to be active at may also rely on heat from the sun to the temperature of the surrounding more slowly but rarely expose warm them up in the morning so that environment. themselves to predators, as they forage they can commence their daily under the leaf litter and in the darker activities. Simon conducted laboratory areas of the forest. experiments by putting skinks in a long Joanna Sumner, a PhD student at The tank which is hot at one end and cold at Skink lifestyle may determine where University of Queensland in Brisbane, the other (Figure 1). He allowed the they prefer to live has been studying the effects of forest lizards to choose the place they liked in fragmentation on one particular skink the tank, and then measured the These differences in lifestyle may species—the prickly forest skink, environmental temperature in that explain the different distributions of the Gnypetoscincus queenslandiae (Figure 2). preferred location. This preferred species in these wet tropical forests. The In particular she has studied population environmental temperature in the tank heliotherm species are capable of living densities, and differences in size and was then compared with the in eucalypt forests, as they have not shape among populations of the lizard temperature in their rainforest micro- given up the heat-loving lifestyle of skink in both rainforest fragments and habitats. The results show that their their more open country relatives. The areas of continuous rainforest. She distribution in rainforest is largely thigmatherms, however, are incapable chose to study the skink populations of dictated by their temperature of moving into hot, dry eucalypt forests the Atherton Tableland where there are requirements, although Joanna’s results - they have become rainforest a large number of rainforest fragments. (below) show that the availability of specialists. The result of this is that suitable homes is also a factor. although thigmatherms can use a Simon and Joanna are both participants greater area of the rainforest, they are in the Rainforest CRC. They have While heliotherms may be vulnerable to less capable of moving between isolated undertaken their research separately, predators such as birds as they sit in the areas of rainforest. Heliotherms such as but there are some interesting sun warming up, they are extremely the red throated rainbow skink (Carlia similarities in their findings. Both quick and rely on their speed to avoid rubrigularis, Figure 3) are fairly common studies are summarised in this being caught. Thigmotherms move information sheet.

Figure 2 Prickly forest skinks are dark brown in colour, with a rough rather than a shiny skin like common garden skinks. After moulting, the striped orange of the skin on their legs is much more visible - most of the time they are too muddy for the stripes to be obvious!

The lengths of these skinks is usually between 30 and 80 mm from their snout to the base of their tails, and they reach maturity at about 50mm. They give birth to between one and five live offspring once a year in the late wet season (Jan - Feb), and groups of baby lizards can often be seen under the same log as their mother during this time. in all the rainforest areas of the wet that increased forest fragmentation and tropics and can be easily found basking clearing may make thigmathermic in sunspots for the majority of the year. species more vulnerable to extinction.

Are changes in light gaps making Simon is continuing his research on the prickly forest skinks vulnerable to distribution patterns of these species extinction? and their preferred temperatures, and this will enable prediction of the effects Simon’s research has shown that there of changes to the environment on these is a minimum canopy opening size fascinating creatures. which the red throated rainbow skink can occupy to ensure that it gets enough For more information about Simon’s sunlight to have time to forage and work, please contact him directly: digest food. These skinks can Simon Cook sometimes be seen chasing each other Zoology Department, James Cook Researcher, Simon Cook out of a particularly favourable sun University, TOWNSVILLE, Qld, 4811 spot. Artificial canopy openings such as Ph: (07) 4781 5742 Fx: (07) 4725 1570 roadsides, have produced far more Email: [email protected] such as crowned snakes (Cacophis habitat for this species than would churchilli) and swamp snakes (Hemiaspis normally be available, as tree fall gaps Are shrinking forests shrinking signata), as well as birds. On one are usually quickly filled by young skinks? occasion Joanna put her hand over a trees. This has allowed the species to skink to catch it and noticed that right expand its range within the rainforest. next to her hand was a small crowned Joanna’s research has concentrated on snake curled up waiting for the right The thigmatherm skinks such as the the prickly forest skink (Gnypetoscincus moment to grab that same skink! prickly forest skink (Gnypetoscincus queenslandiae). She made several field queenslandiae), are more restricted in trips to the Atherton Tableland during Results range, being found only on the several wet and dry seasons and Atherton Tableland and around the surveyed 11 rainforest fragments and Joanna’s results indicate that two factors Daintree area. This skink is a true seven continuous forest sites. Joanna affect population density—the size of rainforest resident. It lives under and finds the skinks by rolling logs and the forest and the number and quality within rotting logs on the rainforest catching them by hand. Captured of the logs available in the forest. floor. Studies have found that prickly skinks are weighed, measured, Smaller forest fragments were less skinks tend to remain in the vicinity of allocated to a sex if mature enough to densely populated with the skinks, as the same log for their lifetime and are determine and then released at the were fragments containing fewer and never found outside the rainforest. point of capture. lower quality habitat sites. Prickly skinks are generally active only on wet nights. They have become such The availability of suitable habitat has As for the skinks themselves, Joanna specialised rainforest animals that it is also been determined. The diet of this found that those in the forest fragments extremely difficult for them to colonise species consists of the insects that share were smaller, weighed less and showed new areas, and so they are basically the rotting log homes, such as some changes in shape compared to restricted to the rainforest patch they cockroaches and pill millipedes. The those captured in continuous forest. are presently inhabiting. This may mean main predators of skinks are snakes

Figure 3 The red throated rainforest skink is usually grey or brown on the back with a pale belly and a copper coloured head. During the breeding season adults of both sexes develop a bright scarlet throat and chin. This colour extends down to the front legs in females and further down the body in males. Some males have a red underside right down to their back legs at the height of the breeding season. The colour on the throat is believed to be used to signal other skinks while not attracting predators.

Females lay two eggs at a time and may have two or three clutches of eggs during a wet season if conditions are good. The eggs are layed at the edge of sun spots in the rainforest and generally take 4-6 weeks to hatch.

Mature rainbow skinks are generally 70-80mm from the tip of the snout to the end of the tail. What do the results mean? increased predation could occur due to best to manage rainforest areas to a relative scarcity of decaying logs in maintain the greatest amount of The differences in size and weight may the forest fragments. This would biodiversity possible. reflect either differences in growth rate account for the average decrease in or survivorship. There are two reasons body size of skinks found in the The animals and plants we find in for differences in growth rate - genetic fragments. rainforest today evolved together to differences between populations and form the intricate web of interactions environmental factors. However, the changes in body that scientists are just starting to proportions as well as overall size untangle. We don’t know the One environmental factor that could suggest that the decreases in population consequences of losing even one species affect growth rate in some species of density are due to more than just from this web that we rely on for clean lizards is food availability. Edge effects predation. Further study will be needed water and air. For this reason it is vital have been studied in Amazonian to determine the causes for the changes that we try to maintain rainforest, rainforest fragments and these have that are being observed. reduce the drastic changes resulting been found to change both the from fragmentation and conserve these abundance and community structure of What are the implications of this vital interactions. insects. If this is the case in the Wet research? Tropics also, the preferred prey of For more information about Joanna’s prickly forest skinks may be in lower These studies examine the quality of the work, please contact her directly: abundance in small fragments. rainforest in fragments. A measure of Joanna Sumner habitat quality is provided by studies Zoology Department, The University of Edge effects may also play a role in the examining the changes in the number of Queensland, ST LUCIA, Qld 4072 changes to body shape that Joanna different species and in individual Ph: (07) 3365 1032 Fx: (07) 3365 1655 observed in the skinks. Edge effects animals. Email: [email protected] resulting from forest fragmentation tend to increase ambient temperature and Joanna’s study and that of other soil temperature on the forest floor, and researchers shows that there are large may also increase temperature numbers of different species in variation. forest fragments, so maintenance and management of these areas is It is known that if skinks experience worthwhile. The simplest way to do this Joanna Sumner with a prickly forest skink either increased average temperatures is to link the rainforest fragments or variation in the temperatures during through rainforest corridors of native pregnancy, newborn lizards have vegetation. significantly different shapes and are smaller. The prickly skinks Joanna Joanna believes it is important to caught in forest fragments showed the encourage landowners to reconnect kinds of changes that would be isolated forests by planting trees along expected from increased or varied rivers and to keep cattle out of the forest temperatures during pregnancy. fragments.

Differences in survivorship offer an Joanna will compare her results on the alternative interpretation for the size effects of fragmentation on reptiles to differences seen between lizard other researchers results for mammals populations from fragmented versus and birds, in order to work out how continuous forest. For example,