Rainforest Fruit Dispersal in Tropical Topics

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 Forest fruit dispersal No. 35 April 1996 Unexpected dispersers Notes from the Wind, gravity and water can move seeds away from the parent plant, but a very high percentage of rainforest species employ animals, paying them with a Editor dispensable fruit layer for their seed dispersal services. Writing some of this issue at home, I was frequently distracted by the While the plant is prepared to supply a tree could hardly wish for a better fate squawking of metallic starlings certain degree of nutrition in this fruity for its offspring. feeding on the fruits of the buttonwood packaging, it invests the lion’s share tree in my garden. Closer to the window, of nutrients in its seeds for the benefit Unfortunately for the seeds, white- preparations are in hand for the of the next generation. Many of these tailed rats are good at finding the October fruit feast, as buds appear on seeds are protected by a hard shell — buried seeds. Perhaps they can smell the corky bark tree. but a number of rainforest animals them or perhaps they remember where have realised that it is worth the effort they buried them — no one knows. Of In temperate climates there is an of penetrating this defence. 1244 seeds whose fate was followed autumn glut of fruit but animals must by CSIRO researchers, 20 percent were include other foods in their diets if Giant white-tailed rats are among the hidden but all were eventually eaten. they are to survive the rest of the year. most voracious of these, using their However, although none of the seeds In the tropics fruit is produced all year exceedingly strong teeth to break into studied ever got a chance to and as a consequence there are many even the hardest nuts. Given the sheer germinate, one remained uneaten for animals, particularly birds, which eat numbers of rats in the rainforests* and 20 weeks which would have been long nothing, or little, else. the thoroughness of their seed enough for seeds of many species to predation (see below) it is actually sprout and grow. It would appear that Since so many animals depend on surprising that any of their favourite one seed, carefully buried and then these fruits and so many trees depend trees survive. forgotten, probably makes up for the on the animals, it is a good idea to help multitudes that are sacrificed for the keep the cycle going by planting those cause. native trees which provide food. You However, it seems that white-tailed can find a list of some on page 7. rats have a habit which works in the trees’ favour. They hide I would like to thank the following seeds. Perhaps they are people for their assistance with this unable to eat all of what they issue: Andrew Dennis, JCU; Stephen find and hide them rather Comport, CSIRO; Graham Harrington, than share them with CSIRO; Bernie Hyland, CSIRO; others or perhaps they Rosemary Lott, JCU; Mike Trenerry, are looking ahead to DoE. lean times. Whatever the Please note reason, this results in that you are welcome to photocopy seeds being taken from Tropical Topics. However, if the below their parent tree, text is reproduced separately it must carried up to 60m away, not be altered and must buried, singly, at a depth of acknowledge the Department of 1-2cm and covered with Environment as the source. lightly compressed soil and a Illustrations must not be reused layer of leaf litter. The parent without permission. Please contact the editor (details on the back page) *Of 10 000 small ground mammals trapped over if in doubt. the past ten years by William Laurance, CSIRO, 98 percent were rats. Quality or quantity? When producing fruits to attract animals, plants have a number of options. One plant may produce a large number of small ‘poor quality’ fruits while another opts for a smaller number of ‘top quality’ fruits. Lilly pillies (Syzygium spp.) are in the former Figbirds love celerywood group. They produce abundant crops of (Polyscias small fruits which are high in water and elegans) sugar content and thus ‘cheap’ to produce (in terms of energy and resources used). Not particularly high in nutrients, they may be a Wompoo pigeon at its nest snack for those animals which include fruits in a mixed diet — but the plant is taking a risk. A number of the consumers are likely to also be seed eaters or to Feeding the youngsters have grinding gizzards which would also destroy ingested seeds. A significant Most animals which eat fruit have to proportion of the seeds from these plants are certain to be doomed. supplement their diet with insects, nectar, pollen and so on. Cassowaries Fruits in the second group, such as some of those in the Lauraceae family, are are known to sometimes eat snails, particularly sought after by those animals which depend on fruit. They need a insects, fungi, flowers and dead more nutritious diet and are offered fruits with a higher content of protein, fat and animals. Only a few animals, mainly oil. Requiring more of the plant’s energy for production, fewer are produced, but birds which can easily move as their consumers, such as cassowaries and fruit pigeons*, are less likely to supplies fluctuate, eat nothing but destroy the seeds. fruit. Fruits in the second category are likely to have a large seed, When raising young, which require perhaps encased in a hard shell. The large seed has less protein to develop, mammals are able chance of being carried far from the parent plant than a to provide protein-rich milk. Birds do small one, but is more likely to produce a strong sapling. not have mammary glands — but those strict frugivores, the fruit *Not all fruit pigeons are soft on seeds. Some, notably the brown cuckoo-dove, have stones in their gizzards and can reduce the pigeons, are able to produce a milk-like seeds of the fruits they eat to a paste. The hairy walnut substance in their crops to feed to (Endiandra insignis), a their chicks. Other fruit-eating birds, nutritious Lauraceae unable to perform this feat, may break fruit . with their vegetarianism and give Fatal attractions insects to their chicks, even if only for Just because cassowaries and other birds, or even mammals like rats, a few days. can eat rainforest fruits, it does not mean that we can also. A very large proportion are very poisonous so please remember — the bright attractive colours are strictly for the birds (and some non- The fruitfly connection human mammals). When the papaya fruit fly was found in north Queensland there were fears that it would spread into Coming attractions the forests of the wet tropics so, in Plants do not want their fruit to be picked before it is ripe. To prevent this some January, DPI staff began a are covered with spines, others lack the attractive scent of the ripe version and rainforest trapping program. They many are colour-coded. Greens and browns camouflage unripe fruits which may plan to continue until the end of turn to red, yellow, black or blue when ripe to advertise their readiness for May to cover the peak of the plucking. It has been said that it is the fruits of the rainforest, rather than the fruiting season. flowers, which produce many of its most vivid colours. A total of 148 traps have been A familiar strategy for rainforest plants is to conceal their seeds in a dull coloured placed in rainforest sites from Noah capsule which splits open when ripe to display a bright red or orange interior with Creek, near Cape Tribulation, to contrasting black seeds or seeds with colourful arils. Josephine Falls and East Palmerston. Happily, very few papaya fruit flies have been found in these traps, most of them in traps located close to roads at Lake Morris, Kuranda and Rex Range. No breeding populations were found. Even better, of 3000 rainforest fruit samples collected Peanut tree none contained the fruit fly. It (Sterculia appears that the flies are attracted quadrifida) primarily to commercial fruits, where pods have a they are much more easily The dull green fruits greenish-brown controlled. of McIntyre’s boxwood exterior but split (Xanthophyllum octandrum) open to reveal a Unfortunately the feral flies are split open when ripe. The bright strongly coloured attracted to the equally feral guava yellow inner lining thus revealed puts orange to vermilion interior, trees which grow in the wild. DPI the black seed on display for the contrasting with half a dozen shiny staff are targetting the trees with a birds. black seeds. herbicide program. 2 Out and about The Great Barrier Reef Marine Park Information Manual, and associated videos, have been produced by Over the past GBRMPA and will be available very few weeks soon. residents of Cairns have been treated The manual is in four components. The showy to the unusual sight Reef Essentials provides a basic fruit of cherry of spectacled flying understanding of how the World beech (Ternstroemia foxes circling around in Heritage Area is managed and how to cherryi) can be seen at this time daylight. Unable to conduct activities in the most of year. Yellow oval fruits split open resist the tempting scent of environmentally responsible manner. It when ripe allowing seeds clothed in their favourite food, melaleuca nectar, is accompanied by a 60min.

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