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Ornithology, Evolution, and Philosophy 123

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Zoogeography 179<br />

Fig.4.14. Secondary hybrid belts among tree runners (Neositta) ofAustralia.Thearrows<br />

indicate expansion from Pleistocene aridity refuges. Wherever former isolates have met,<br />

they have formed hybrid belts (indicated by hatching). R, subspecies with red wing bar; W,<br />

subspecies with white wing bar. From Mayr (1963b: 373)<br />

As to the differentiation of Australian birds at low taxonomic levels Mayr (1950b)<br />

conceived a theory of speciation <strong>and</strong> subspeciation in tree-runners (Neositta): During<br />

a Pleistocene or post-Pleistocene arid period (or several periods) a previously<br />

widespread ancestral species had been separated into a number of moist refuges<br />

around the periphery of the continent, where these isolated populations acquired<br />

the diagnostic characters of the taxa of this genus now recognized (Fig. 4.14). After<br />

the return of more humid conditions the previous isolates spread out from the<br />

refuges together with the exp<strong>and</strong>ing vegetation zones, hybridizing in the areas<br />

where they came in contact with one another. Keast (1961) <strong>and</strong> Short et al. (1983)<br />

strongly supported this interpretation. It was the first detailed presentation of the<br />

refuge theory of Pleistocene speciation for birds of the southern hemisphere. Zoogeographers<br />

had proposed similar models for the differentiation of European birds<br />

<strong>and</strong> other animals which were assumed to have survived in humid Mediterranean<br />

refuges during the generally dry glacial periods.<br />

Malay Archipelago<br />

A schematic eastern delimitation of the Indomalayan Region follows the border<br />

of the Pleistocene Sunda l<strong>and</strong> from the straits between Bali <strong>and</strong> Lombok in the

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