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relatively few Asian or Australian mammals (Cox
and Moore 1993), and in part because other groups
of more dispersive animals, such as birds, butter-
flies, and reptiles, show the filter effect (see Fig. 3.4)
rather than an abrupt line. Another problem for the
drawers of lines is that the insects of New Guinea
are mainly of Asian origin. There are several such
enigmas of distribution in relation to these lines:
for a fuller discussion see Whitmore (1987) and
Keast and Miller (1996). Perhaps the best option is to
restrict the Oriental and Australia regions to the

limits of the respective continental shelves, and to

treat the intervening area of Wallacea as essentially

outside the framework of continental biogeography

(Cox 2001).

The placing of distant oceanic islands into this

sort of traditional biogeographical framework has

drawn criticism from Carlquist (1974, p. 61) who

has argued that because of the isolation of islands,

and their differing histories from continents, their

biotas provide very poor fits with regional biogeo-

graphical divisions. Commonly, oceanic islands

DISHARMONY, FILTERS, AND REGIONAL BIOGEOGRAPHY 53

Hawaii

Marquesas

Pitcairn Easter

Island

Cook Is.

Society Is.

Tonga

Samoa

New Fiji

Caledonia

New Guinea

12

3

(^45)
6
7
120 °E 140 ° 160 ° 180 ° 160 ° 140 ° 120 °W
40 °S
20 °
0 °
20 °
40 °N
Figure 3.3Eastern limits of families and subfamilies of land and freshwater breeding birds found in New Guinea. The decline in taxa is fairly
smooth, and shows both differences in dispersal ability and that there is a general decline in island size to the east. Not beyond: 1, New Guinea
(14 taxa), pelicans, snakebirds, storks, larks, pipits, logrunners, shrikes, orioles, mudnesters, butcherbirds, birds of paradise, bowerbirds, Australian
nuthatches, Australian tree-creepers; 2, New Britain and Bismarck islands (2 taxa), cassowaries, quails, and pheasants; 3, Solomon Islands (10
taxa), owls, frogmouths, crested swifts, bee-eaters, rollers, hornbills, pittas, drongos, sunbirds, flower-peckers; 4, Vanuatu and New Caledonia (7
taxa), grebes, cormorants, ospreys, button-quails, nightjars, wren warblers, crows; 5, Fiji and Niuafo’ou (4 taxa), hawks, falcons, brush turkeys,
wood swallows; 6, Tonga and Samoa (7 taxa), ducks, cuckoo-shrikes, thrushes, whistlers, honeyeaters, white-eyes, and waxbills; 7, Cook and
Society islands (3 taxa), barn owls, swallows, starlings; 8 (beyond 7), Marquesas and Pitcairn group, herons, rails, pigeons, parrots, cuckoos, swifts,
kingfishers, warblers, and flycatchers. Others: owlet-nightjars, one species from New Caledonia, otherwise limit 1; ibises, one species from the
Solomon Islands, otherwise limit 1; kagu, endemic family of one species from New Caledonia. (From Williamson 1981, Fig. 2.5. We have not
attempted to update this figure in the light of more recent fossil finds.)