Tropical Topics A n i n t e r p r e t i v e n e w s l e t t e r f o r t h e t o u r i s m i n d u s t r y Rainforest possums Vol 1 No. 7 November 1992 Possum Notes from the patterns Editor The Atherton and Evelyn Tablelands, where rainforest exists next to areas of tall open eucalypt Long-tailed pygmy possum forests, is home to one of the largest concentrations of possums in About 15 million years ago Australia, Australia. It is possible (in theory!) moving north, bumped into the Asian to see 13 species of possums and continental plate. This collision allowed an gliders within an area of a few exchange to take place between two sets of flora and kilometres. fauna which had evolved in isolation. Asian flora and fauna, including many placental rats, moved into This month’s Tropical Topics deals Australia. At the same time Australian species moved north. Many animals with the rainforest species, colonised Papua New Guinea, a new high altitude land mass which had been specifically the green, lemuroid, created by pressure between the Asian and Australian plates. Some, like the Herbert River and Daintree River Dorcopsis wallaby, thrived in their new home while relatives left in Australia ringtails, the coppery brushtail, the became extinct. striped possum and the long-tailed Changing climatic conditions caused Because cuscuses (possums related to pygmy possum. Some of the open Australia to dry out. Rainforest which brushtails) are found only in northern forest possums, notably the sugar had covered much of the continent Cape York, they were assumed to have glider, do enter the rainforest but retreated to ‘refugia’ — river valleys originated in New Guinea, moving to there is a fairly clear distinction and cool, moist mountain tops. Then, Australia only quite recently. Fossils between rainforest and open forest about 8000 years ago, the climate of ancient (and extinct) cuscuses types. To tackle all in one short became wetter and the rainforests discovered in Queensland and issue would lead to overload, so we expanded again. Victoria, however, turned this story have decided to keep the open around. It is now believed that these forest possums and gliders for a Today’s Wet Tropics possum animals were once widespread in future issue. distributions reflect these changes. Australia but died out, possibly during The rainforest ringtails — the green, its driest period about lemuroid, Herbert River and Daintree 18 000 years ago. Those which had Readers of (or glancers at) Tropical River ringtails — remained in the already moved to New Guinea thrived, Topics often react with surprise rainforests, retreating with them into two species eventually returning to when they discover a marine item in the refugia sites and expanding their Australia as conditions there a Wet Tropics issue and vice versa. range again when conditions became improved. Since every issue goes to both wetter. As ‘relict’ species they have groups of tour operators we try to evolved very little and survive in Working out this ancient puzzle is a include something of interest for primitive forms. slow process and the discovery of everyone. different pieces means that the story is Other species adapted to the drier constantly being rewritten. Many conditions; the common ringtail, the questions remain. The distribution of brushtail and the sugar glider evolved the long-tailed pygmy possum, for to survive in open forests. Later, to a example, still poses problems because certain extent, they re-entered the it exists in New Guinea and Australia rainforest to live alongside the relict but is absent from northern Cape York ringtail species, although they are in between. It will be some time before more commonly seen in open forests. scientists are able to answer all the questions. Diets and dens poisonous, non-nutritious and/or therefore the most energetic of the tough. To counter these protection three ringtail possums, leaping strategies, animals have become very between trees and returning to a fixed selective in choosing their leafy meals den at the end of the night’s activity. and have also cultivated some useful friends... gut microbes. In contrast to the lemuroid possum, the green ringtail is the sloth of the The only organisms able to digest rainforest. Its diet consists of tough plant fibre are special microbes found and poisonous fig leaves, the leaves of in the stomachs of all animals, from some laurels and even those of the termites to humans, which eat shining stinger! Such a diet is low in plants. Certain micro-organisms energy but easy to find, because there can also break down the are few other animals wanting to eat poisons found in leaves but such poor quality food. Green ringtails this requires a lot of energy. therefore do not have to search far for These useful microbes are so something to eat. Then, at the end of important to possums that they the night, these low-energy possums have provided a special home save on fuel by curling up wherever for them, the caecum. The human they are. Consequently, green ringtails appendix is the equivalent of don't have a fixed den but change their the caecum. However while sleeping site nightly, depending on the the human appendix is small location of their last meal. (we don’t rely on plant fibre to survive), the possum’s Herbert River ringtails feed on caecum is large, reflecting regrowth species such as sarsaparilla Green ringtail its vegetarian diet. (Alphitonia petriei) and quandongs possum such as Elaeocarpus ruminatus. Their Research has found energy intake falls somewhere between The rainforest ringtail possums that not only are that of the green and the lemuroid are primarily leaf eaters, taking an possums very selective eaters, but ringtails, and so does their den occasional snack of flowers and fruits their behaviour also depends largely requirement. ‘Herbies’ will return to on the side. Not all leaves, however, on the energy available in their diet. dens if they are close to home at the are edible. Lemuroid ringtails choose leaves low end of the night’s activities. Otherwise, in fibre such as the young leaves of they will not waste energy and often As leaves are a plant’s solar cells, Queensland maple (Flindersia prefer to camp in nearby epiphytic essential for survival, plants protect brayleyana) and white carabeen ferns. them from insect and mammal (Sloanea langii). Because they use predators. Common protection less energy to digest their food they methods involve making the leaves have more to spend. This species is Acknowledgments to Dr Nicky Goudberg. Possums and patches Research shows that different species which never comes of possums can co-exist in the same down to the area of rainforest by feeding on ground. different plants. This variation in diet, Unfortunately its and related lifestyle, leads to different diet consists responses to destruction and largely of mature fragmentation of forest. rainforest tree foliage, Green ringtails and coppery brushtails particularly are the most adaptable and can be those cabinet found in quite small patches of forest timber trees as well as in disturbed areas. These which are the animals feed on secondary growth target of loggers. and pioneer species which commonly It needs a den for daytime result from disturbance, as well as resting and does not live in species such as fig trees which are secondary forest. Its reluctance to not removed by loggers. They are come to the ground reduces its ability also willing to travel along the to move to other areas when its home is disturbed. Of the leaf-eating Lemuroid ringtail ground, even through open areas possum away from rainforest, enabling them to rainforest possums it is the least able move between small forest patches. to survive in remnant patches, The green ringtail is not dependent on disappearing from small fragments den sites such as tree hollows or within nine years and from fragments secondary trees. It is less of a canopy epiphytic ferns. of 40-80ha within 35-60 years. dweller and will come to the ground, enabling it to escape from areas which Lemuroid ringtails and Herbert River The Herbert River ringtail has similar are disturbed. Numbers decline sharply ringtails are more vulnerable. The dietary and den requirements to the in areas under 20ha in size. lemuroid is a high canopy dweller lemuroid but is able to feed on some Acknowledgments to Dr Bill Laurance Possum tucker Possum’s got a belly ache Possum lives in possum land Positively crook A finely balanced state Spare a thought for possum’s sake Feeding possum from the hand ‘Cos possum’s not a sook Endangers possum’s fate Possum lives on forest food By all means look and listen Not on tourist snacks And savour possum’s play Possum doesn’t feel too good But keep the tucker hidden It’s sympathy he lacks Let possum live his way! Robin Filkin Possums and humans do not have population balances. Generally it is food are also in danger from dogs. the same digestive systems. If fed the brushtails which will approach If you must feed a possum, please a diet of leaves our health would humans for handouts. This artificial give it fruit or carrot (avoid suffer. Similarly, possums cannot increase in food supply leads to a cabbage and other brassicas). cope with bread and other ‘human’ population boom in that particular However, with a little effort, foods. They might as well be species. Other types of possum are careful spotlighting will reveal a eating cotton wool. It makes them pushed out of the area and the greater variety of possums without feel full so they eat fewer leaves, diversity of species decreases.