Biogeographical and avifaunal boundaries.
On May 12, Iain Campbell asked about biogeographical boundaries. A very
interesting subject and one which I have done much research on during the
last 2 years while compiling a complete (are these things ever complete?)
bird list for Australasia.
Wallace's original six faunal regions, that he proposed in ?1873, are still
recognised today. They are Neotropic, Neartic, Ethiopian, Eurasian,
Oriental and Australasian.
The avifaunal regions are the same, but some avifaunal boundaries have long
differed from Wallace's original boundaries, particularly in regard to
Wallacea. Most ornithologists have recognised Weber's Line as the
Australasian-Oriental boundary for some decades now.
Avifaunal Regions are adjoining. The boundaries of Avifaunal Regions often
follow continental plate boundaries e.g. the Mid-atlantic Ridge divides the
Neotropical Region from the Ethiopian Region, and the Nearctic from the
Eurasian.
The Australasian Avifaunal Region evolved around what is now Australia and
New Guinea, which was on the south-eastern side of the Indo-australian
continental plate. The remoteness of this 'Greater Australia' from all
other continents after the break-up of Gondwana meant that passerine
evolution here continued in complete isolation until relatively recently.
The Australasian Region boundaries the other five regions, and comprises
the Sub-regions of Australia, Southern Melanesia, New Zealand, all of
Polynesia, Micronesia, Papuasia, the eastern and southern islands of Maluku
(the Moluccas), and part of Antarctica.
Because of Greater Australia's close proximity to the islands and
continental remnants of the Pacific plate, many species that evolved in
Australia spread eastward, over halfway across the Pacific, throughout the
area that has loosely been described as `Oceania'. The Australasian region
includes Easter Island and the Hawaiian Islands, indeed, most of the
Pacific.
The Australasian boundary crosses the international dateline about 42
degrees N.and brushes with the Eurasian Region S.E. of Japan. (The Eurasian
region runs from here to Iceland and south to the Sahara-Arabian Deserts).
The boundary then goes to the S.E. of the Philipines (in the Oriental
Region), and instead of following Wallace's Line through the Straits of
Makassar, now follows Weber's Line through the Moluccas, along the probable
continental plate boundary.
It goes W. of Halmahera and Buru, leaving the Sula Islands in the Orient,
and swings through the Banda Sea to go between Babar Is (Oriental) and the
Tanimbars (Australasian). It then follows the Java Trench which is S. of
the Lesser Sundas leaving that archipelago in the Oriental Region. I had
thought that at least Timor and Sumba had about a 50/50 sharing of Oriental
and Australasian species, but Paul Andrew assures me that Mayr's review of
Timor avifauna put it with
Oriental. The Oriental Bird Club includes Wallacea in the Oriental Region.
And the Species List of the Birds of Australasia?
`Final' count was 1905 species of which 1325 are endemic. There are 64
introduced, 83 vagrant, and 1726 breeding or regular migrant, species. No
known extinct species are included.
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Andy Anderson
fax/ph 61/70 323387
Box 7999 Cairns 4870,
Australia
Andrew P.Anderson's Box 7999 Cairns 4870,Australia
AUSTRALASIAN BIRDING SERVICES
Australia-New Zealand-New Guinea-S.W.Pacific fax/ph 61/70 323387
Showing the Birds of Australasia to the People of the World
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