Ornithology, Evolution, and Philosophy 123

Zoogeography 175
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