New Guinea

New Guinea forms one zoogeographical unit with Australia, as shown by the lack of placental mammals (except for bats and some rodents) and the wealth of marsupials. The bird fauna of New Guinea resembles the mammalian fauna in the strong prevalence of groups which it has in common with Australia (Mayr 1954k). Papuan or Australo-Papuan families and subfamilies include those with the highest number of New Guinea species, like the Meliphagidae (61), Malurinae (24), and Pachycephalinae (24). At the level of genera the Australo-Papuan elements also far outweigh the Indomalayan (Asiatic) elements, the other major faunal group represented in New Guinea; and there is a high degree of striking endemism in the Papuan Region. The Moluccan Islands are inhabited by an impoverished Papuan bird fauna with a considerable admixture of Asiatic elements.

In contrast to these relationships of the faunas, the flora of the tropical belt from Malaya through New Guinea to the Solomon Islands and Polynesia forms one phytogeographical unit (Malesia) which differs strikingly from the flora of temperate and warm-dry Australia. The reasons for this difference between the zoogeographic and phytogeographic situation are according to Mayr (l.c.): Dispersal between Malaya and New Guinea demanded island hopping, but birds, in spite of their mobility, are easily stopped by ocean barriers. On the other hand plants disperse without difficulties across water gaps if the land area beyond the water barrier is located within the same climatic zone. The repeated and sometimes long lasting connections between New Guinea and Australia permitted a free faunal interchange. The nearest relatives of many rainforest birds of New Guinea inhabit brush savannas and semideserts of Australia. Such ecological shifts are much more difficult for plants (and certain invertebrates). Their establishment after dispersal is more closely dependent on climatic and edaphic factors than that of birds. These facts explain the striking differences between the floras of New Guinea and Australia in contrast to the respective bird faunas.

Nothing was known about climatic-vegetational changes in the tropical lowlands of New Guinea and corresponding faunal movements during recent geological periods, when Ernst Mayr traveled in these regions. Botanists had suggested that the grass savannas around Lake Sentani near Hollandia (Jayapura) in northern New Guinea (Fig. 2.8) had originated through deforestation by man. Mayr was immediately doubtful of such an interpretation because he found several endemic subspecies of birds to inhabit these savannas (e. g. Lanius schach stresemanni, Saxicola caprata aethiops, etc.) indicating a very old age and a natural origin of these plant formations. They had been merely enlarged through later rainforest clearing. In his expedition report Mayr (1930f: 25) stated with respect to the grasslands around Lake Sentani:

"The many indigenous subspecies prove that the grassland must be of very old origin. Nowadays the natives burn the grass regularly, and the forest is going back every year, but I am convinced (contrary to the opinion of botanists) that this grassland here is a very old one. It is isolated now more or less from the grassland patches of Eastern New Guinea, but I think that in former geological periods the

Pied Bushchat (Saxícola caprata)

Fig. 4.13. Distribution of the Pied Bushchat (Saxicola caprata) in the Malay Archipelago and in New Guinea from where this open-country species of Asian origins has reached only the Bismarck islands of New Britain and New Ireland and the nearby recently defaunated volcanic islands of Long and Uatom. Like most other open-country colonists of Northern Melanesia, it has scarcely differentiated: the Bismarck populations still belong to the same subspecies as the New Guinea source population. From Mayr and Diamond (2001, map 31) and bird sketches from MacKinnon and Phillipps (1993, plate 71)

Pied Bushchat (Saxícola caprata)

Fig. 4.13. Distribution of the Pied Bushchat (Saxicola caprata) in the Malay Archipelago and in New Guinea from where this open-country species of Asian origins has reached only the Bismarck islands of New Britain and New Ireland and the nearby recently defaunated volcanic islands of Long and Uatom. Like most other open-country colonists of Northern Melanesia, it has scarcely differentiated: the Bismarck populations still belong to the same subspecies as the New Guinea source population. From Mayr and Diamond (2001, map 31) and bird sketches from MacKinnon and Phillipps (1993, plate 71)

steppe had a much wider distribution in New Guinea than now" and in a letter to Erwin Stresemann dated 25 April 1939 discussing the distribution pattern of the Pied Bushchat (Saxicola caprata; Fig. 4.13) Mayr wrote: "I believe that at some time in the past there was a drier zone along the north coast of New Guinea which was the immigration route of this form. The three species which I discovered in the Arfak Mountains: Megalurus timoriensis, Acrocephalus arundinaceus and Lonchura vana are an indication of this line of immigration. There are quite a number of the savanna species which have not reached Australia. I am fairly convinced that these species reached eastern New Guinea via the Moluccas and western New Guinea. These species are Saxicola caprata, Merops philippinus, and Lanius schach" (see Haffer 1997b: 509). Saxicola caprata probably did not have to fly across the ocean from the Philippines to eastern New Guinea, as tentatively indicated on Fig. 4.13, but was able to hop from one island to the next through the Moluccas and western New Guinea during a cool-dry climatic period of the recent geological past, when these regions were partially covered with open nonforest vegetation.

Similarly, the fact that the grasslands of the island of Guadalcanal, one of the Solomon Islands, are the home of two endemic subspecies of birds (a finch and

Table 4.2. Degree of endemism in montane species of Passeres on three New Guinea mountains (after Mayr 1940c); two percent values under Arfak slightly changed

Arfak Cyclops Saruwaget

Table 4.2. Degree of endemism in montane species of Passeres on three New Guinea mountains (after Mayr 1940c); two percent values under Arfak slightly changed

Arfak Cyclops Saruwaget

Not endemic

36 =

40.4 %

21 =

72.4 %

59 =

68.6 %

Endemic subspecies

46 =

= 51.7%

8=

27.6 %

23 =

26.7 %

Endemic semispecies

5 =

= 5.6 %

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