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BATS
AND MANNA GUM TREES |
There are approximately 500 species of Eucalyptus trees. Fujita (1991) lists 40 Eucalyptus species as being pollinated by three species of flying foxes; the black flying fox (Pteropus alecto), the grey-headed flying fox (P. poliocephalus) and the little red flying fox (P. scapulatus.
Grey-headed flying fox (Pteropus poliocephalus)
Eucalyptus flowers
One of the manna gum trees, Eucalyptus viminalis, is listed by Fujita as being pollinated by the grey-headed flying fox. The manna gum tree is also a honey tree. Bees as well as bats seek out the sweet nectar of the tree's flowers.
The manna gum tree is so named because a sweet red gum oozes from the leaves and damaged bark. The gum was eaten in early times by aboriginal Australians. It is still collected and savoured by human beings.
Manna gum medicine: Manna gum has a mild laxative effect. Oil from the leaves fights influenza viruses. Aching limbs can be relieved by a soak in a decoctation of manna gum leafy twigs.
Manna gum timber: The Oxford Dictionary of Trees says that E. viminalis is of little commercial importance, but the database of Plants for a Future disagrees. That source says that E. viminalis has wood of "excellent quality" which is used in building and joinery. The wood does not rot in contact with earth. The wood can be converted to paper pulp.
Other uses: E. viminalis is a source of a multi-use essential oil. The sweet leaf and bark manna is incorporated into adhesives and the bark is a source of tannin.
E. viminalis apparently transpires water from its leaves at a high rate. This is suggested by the fact that tree has been planted in southern Europe where it combats mosquitoes by draining marshes.
Koala bears: Those who celebrate the existence of koala bears would also celebrate the fact that some bat-pollinated eucalyptus trees are foraged for leaves by koala bears.
The National Koala Survey, 1985-1987, did not record E. viminalis as one of the trees in which koalas were most frequently observed, even though E. viminalis was a dominant species in the forest where koalas were most abundant. Another gum tree in which koalas were observed, the Red River gum (E. camaldulensis) is pollinated by the little red flying fox and the black flying fox.
The Australian Koala Foundation has conducted a survey of koala use trees which it states is not exhaustive. Eleven eucalyptus species are listed, six are starred as key species. E. viminalis, the manna gum tree, is included in the list, but it is not starred as a key species. E. camaldulensis, Red River gum, mentioned above, is also listed a koala use tree, but it is not starred as a key species.
Eucalyptus species, Maui, Hawaii
Photograph courtesy of Forest & Kim Starr (USGS)
However, three of the six key species, E. microcorys, tallowwood, E. propinqua, small fruited grey gum, and E. tereticornis, forest red gum, are listed by Fujita as being pollinated by one or all three of the three flying foxes which pollinate E. viminalis; grey-headed flying fox, black flying fox and little red flying fox.
Indeed, Raymond Island Koalas Information Sheet states that 50 of the some 500 species of Eucalyptus trees are used for food by koala bears. Existing information seems to establish that some of the eucalyptus trees preferred by koala bears are pollinated by flying foxes.
Koala bears and the White Naped Honey Eater: Koalas do forage in E. viminalis trees in the Mount Lofty Ranges, south Australia. E. viminalis is identified as one of two gum trees in the Mount Lofty Ranges, upon which a nectar-drinking bird, the white naped honey eater, depends for manna to supplement its nectar intake. The other tree is the South Australian Blue Gum, E. leucoxylon.
Koala bears have been introduced into this area because many of the eucalyptus forests on which they historically depended have been cut down for commercial use and reforestation has not kept pace with forest destruction. The koala bear population in Australia has declined. Now the population stability of the white naped honey eater is being eroded because of the relocated koala bears' need for one kilo of leaves daily which they are collecting at least in part from the two eucalyptus species of trees upon which the bird relies for manna.
Flying foxes and koala bears:
In Australia both species of animals are suffering from habitat loss. An 2001
article by Patrick Barkham, a Sydney correspondent, in the Guardian stated:
" . . . Australia is the sixth highest clearer of land in the world,
destroying more native forest than any other developed country. More than
80 percent of the koala's habitat has been destroyed since the white settlement
began 200 years ago." In the same article Deborah Tabart, then the executive
director of The Australian Koala Foundation was quoted as saying: "There
are not too many koalas, there are too few trees."
Little red flying fox (Pteropus scapulatus)
The koalas' habitat loss is also a habitat loss for flying foxes. The surviving koala population are eating the leaves of trees in areas that are protected remnants of original forests and investigating trees in city suburbs. Flying foxes, also forced by habitat loss into human contact, are invading commercial fruit orchards and denuding trees in treasured, long-established botanic gardens. Both animals lose their lives, the koalas to cars and cats, the bats to legal and illegal control measures.
References:
Australian Koala Foundation;www.savethekoala.com/koalatrees.html
Barkham, Patrick, Save trees-put koalas on the pill, The Guardian, Tuesday, 6 November 2001, page 15
Effect of habitat dedgredation and enhancement on persistence of the White Nape Honeyeater in Mount Lofty Ranges, South Australia; www.ssn.flinders.edu.au/geog/postgrad/Harper.php
Fujita, M.S. 1991. Flying Fox (Chiroptera:Pteropodidae) Pollination, Seed Dispersal, and Economic Importance: A Tabular Summary of Current Knowledge, Resource Publication No. 2, Bat Conservation International
Parks Victoria: Koala Management and Fertility Control, Spring 2005;www.parkweb.vic.gov.au/1process_content.cfm?section=89&page=25
Plants for a Future: Database Search Results; www.ibiblio.org/pfaf/cgi-bin/arr_html
Royal Botanic Gardens, Kew (1999). Survey
of Economic Plants for Arid and SemiArid Lands (SEPASAL)database. Published
on the Internet;http://www.rbgkew.org.uk/ceb/sepasal/internet/
[accessed 7 January 2007 1000 hours]