Specialtion in the genus Amytornis Stejneger (Passeres: Muscicapidae, Malurinae) in Australia.

Abstract

The present paper discusses and determines the status of a range of forms and species in the genus Amytornis Stejneger (Australian grass-wrens), reviews infraspecific variation and re-defines races, and makes a study of speciation in the genus. In demonstrating the various stages in the speciation process Amytornis provides a parallel with Climacteris Temminck (Keast 1957). The genus is particularly rich in distinctive isolated forms that, though they have never had their true status tested by contacting the parental stocks, are nevertheless so different that, if normal taxonomic procedure be applied, they must be regarded as species. There is one demonstration of the ultimate stage in the speciation process, that of two former isolates secondarily coming together and demonstrating their distinctness by failing to interbreed. Amytornis contrasts with Climacteris in that it is fundamentally a desert genus, with spinifex the basic habitat. Hence isolation of populations would appear to have resulted, in the main, not from increasing aridity, but as a result of the invasion of former spinifex or porcupine grass areas by savannah grassland (an unsuitable habitat as it provides cover for only part of the year). Changes in the colour and colour pattern of the birds and in size and bill form (inferring a change in the food) of Amytornis provide, to a degree, a continental example of the kind of speciation seen in some island archipelagos, e.g. Galapagos Is. (Lack 1947). The application of Gloger's and Bergmann's ecogeographical rules to members of the genus Amytornis is discussed.