Studbook nr. 5, December 2008

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EUROPEAN STUDBOOK CROWNED PIGEONS " an array of populations which are actually or potentially interbreeding, and which are reproductively isolated from other such arrays under natural conditions (Mayr, 1942)." In other words, a species is a group of organisms that interbreed and produce fertile offspring only with one another. Mayr's definition has enjoyed the broadest popularity of any definition offered for species, but there are both practical and conceptual difficulties with it's application during the course of biological classification. The three species of crowned pigeons are, in contradiction to the definition of a species, hybridizing. Both in the wild and in captivity, hybrids can be found. McMorris (1976) expects that the Goura scheepmakeri is a result of hybridization between Goura victoria and Goura cristata. These species both occur at the Siriwo River in the northeast of New Guinea and they are hybridizing there too. The northern border of the range of Goura scheepmakeri is not far from this point, so it might be possible that the hybrids have moved and settled themselves in the southern part of New Guinea. This seems very plausible, also because of the colours of the different species. In addition, comparing studies of the behaviour of the three species did not show any differences in the behaviour of the species (Lommers, 1982; Van Rijn 1995). For this reason, it is probably better to call the three species geographical races. But, geographical races may in time come to differ so much from their parent stock that they evolve into new species (Goodwin, 1983). Probably in the past the three species of crowned pigeons were geographical races, derived from one species. They could have disappeared from large areas of its range through alteration of the habitat, leaving isolated populations separated by areas of country no longer suitable for it. When they came together again they have differed so much from their parent own stock, that they have been evolved into a new species (Beehler, 1981). The island of New Guinea used to be part of Australia (Pratt,1981) and at the edge of two plates, New Guinea is tectonically active, with a considerable history of mountain-uplift, volcanic activity and earthquakes. Today this is a still continuing process (Beehler et al., 1986). In New Guinea several different geographical sub regions can be distinguished, each with some characteristic flora and fauna. Lowland rainforest occurs along the entire coast, being broken in a few places by anthropogenic grassland or eucalypti savannah. However, at the moment large areas of tropical rainforest occur only in three regions: • The vast Fly Platform south of the Central Ranges, extending from about Etna Bay at the neck of the Vogelkop to Hall Sound on the SE peninsula, home of the Scheepmaker’s crowned pigeons • In the west, the Vogelkop peninsula, where the common crowned pigeons occurs, and • In the north, the watershed of the Mamberambo River and its tributaries and adjacent coastal plains, and the Sepik and Ramu basins. In this area the Vicoria’s crowned pigeons occur. Most of the islands, where crowned pigeons occur, are co-called ‘land-bridge islands’. Land-bridge islands were in the past connected to the mainland (New Guinea), but since the sea level has risen, they became isolated (Diamond, 1973). This development has taken place only recently. Conclusion Sometimes it is easy to determine species and subspecies, but because of the continuous evolution of the earth, there are always mixed forms. Without doubt, all forms of crowned pigeons derive from one species and they might have become separated by environmental and climatic changes. They differ already a lot in phenotype, and DNA-research proved that their genotype is also quite different. 162
EUROPEAN STUDBOOK CROWNED PIGEONS At the land-bridges, for example, there are lot of forms which resemble the nominate form very much. This development did take place not that long ago; therefore it might be possible for some forms to produce fertile offspring with forms on nearby islands. At this moment it is preferable to call these forms “sub-species”, and the three forms with large differences “species”. But like nature itself also these classifications should not be fixed, but always be susceptible to changes. 163
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Studbook nr. 5, December 2008

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