the malay archipelago-1-第54章
按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
first sight suppose that this is due to the wide sea that separates Australia from Timor。 But this would be a hasty and； as we shall soon see； an unwarranted supposition。 Besides these birds identical with species inhabiting Java and Australia； there are a considerable number of others very closely allied to species peculiar to those countries； and we must take these also into account before we form any conclusion on the matter。 It will be as well to combine these with the former table thus：
In Lombock。 In Flores。 In Timor。 Javan birds 。 。 。 。 。 。 。 。 。 。 。33 23 11 Closely allied to Javan birds 。 。 1 5 6 Total 。 。 。 。 。 。 。 。 。 。 。 。 。 。 34 28 17
Australian birds 。 。 。 。 。 。 。 。 。 4 5 10 Closely allied to Australian birds 3 9 26 Total 。 。 。 。 。 。 。 。 。 。 。 。 。 。 7 14 36
We now see that the total number of birds which seem to have been derived from Java and Australia is very nearly equal； but there is this remarkable difference between the two series： that whereas the larger proportion by far of the Java set are identical with those still inhabiting that country； an almost equally large proportion of the Australian set are distinct； though often very closely allied species。 It is to be observed also； that these representative or allied species diminish in number as they recede from Australia； while they increase in number as they recede from Java。 There are two reasons for this； one being that the islands decrease rapidly in size from Timor to Lombock； and can therefore support a decreasing number of species； the other and the more important is； that the distance of Australia from Timor cuts off the supply of fresh immigrants； and has thus allowed variation to have full play； while the vicinity of Lombock to Bali and Java has allowed a continual influx of fresh individuals which； by crossing with the earlier immigrants； has checked variation。
To simplify our view of the derivative origin of the birds of these islands let us treat them as a whole； and thus perhaps render more intelligible their respective relations to Java and Australia。
The Timor group of islands contains：
Javan birds 。 。 。 。 。 。 。 36 Australian birds 。 。 。 13 Closely allied species 。 。 11 Closely allied species 。 。 35 Derived from Java 。 。 。 。 47 Derived from Australia 。 。 。 48
We have here a wonderful agreement in the number of birds belonging to Australian and Javanese groups； but they are divided in exactly a reverse manner； three…fourths of the Javan birds being identical species and one…fourth representatives； while only one…fourth of the Australian forms are identical and three…fourths representatives。 This is the most important fact which we can elicit from a study of the birds of these islands； since it gives us a very complete clue to much of their past history。
Change of species is a slow processon that we are all agreed； though we may differ about how it has taken place。 The fact that the Australian species in these islands have mostly changed； while the Javan species have almost all remained unchanged； would therefore indicate that the district was first peopled from Australia。 But； for this to have been the case； the physical conditions must have been very different from what they are now。 Nearly three hundred miles of open sea now separate Australia from Timor； which island is connected with Java by a chain of broken land divided by straits which are nowhere more than about twenty miles wide。 Evidently there are now great facilities for the natural productions of Java to spread over and occupy the whole of these islands； while those of Australia would find very great difficulty in getting across。 To account for the present state of things； we should naturally suppose that Australia was once much more closely connected with Timor than it is at present； and that this was the case is rendered highly probable by the fact of a submarine bank extending along all the north and west coast of Australia； and at one place approaching within twenty miles of the coast of Timor。 This indicates a recent subsidence of North Australia； which probably once extended as far as the edge of this bank； between which and Timor there is an unfathomed depth of ocean。
I do not think that Timor was ever actually connected with Australia； because such a large number of very abundant and characteristic groups of Australian birds are quite absent； and not a single Australian mammal has entered Timor which would certainly not have been the case had the lands been actually united。 Such groups as the bower birds （Ptilonorhynchus）； the black and red cockatoos （Calyptorhynchus）； the blue wrens （Malurus）； the crowshrikes （Cracticus）； the Australian shrikes （Falcunculus and Colluricincla）； and many others； which abound all over Australia； would certainly have spread into Timor if it had been united to that country； or even if for any long time it had approached nearer to it than twenty miles。 Neither do any of the most characteristic groups of Australian insects occur in Timor； so that everything combines to indicate that a strait of the sea has always separated it from Australia； but that at one period this strait was reduced to a width of about twenty miles。
But at the time when this narrowing of the sea took place in one direction； there must have been a greater separation at the other end of the chain； or we should find more equality in the numbers of identical and representative species derived from each extremity。 It is true that the widening of the strait at the Australian end by subsidence； would； by putting a stop to immigration and intercrossing of individuals from the mother country； have allowed full scope to the causes which have led to the modification of the species； while the continued stream of immigrants from Java； would； by continual intercrossing； check such modification。 This view will not； however； explain all the facts； for the character of the fauna of the Timorese group is indicated as well by the forms which are absent from it as by those which it contains； and is by this kind of evidence shown to be much more Australian than Indian。 No less than twenty…nine genera； all more or less abundant in Java； and most of which range over a wide area； are altogether absent； while of the equally diffused Australian genera only about fourteen are wanting。 This would clearly indicate that there has been； until recently； a wide separation from Java； and the fact that the islands of Bali and Lombock are small； and are almost wholly volcanic； and contain a smaller number of modified forms than the other islands； would point them out as of comparatively recent origin。 A wide arm of the sea probably occupied their place at the time when Timor was in the closest proximity to Australia； and as the subterranean fires were slowly piling up the now fertile islands of Bali and Lombock； the northern shores of Australia would be sinking beneath the ocean。 Some such changes as have been here indicated； enable us to understand how it happens； that though the birds of this group are on the whole almost as much Indian as Australian； yet the species which are peculiar to the group are mostly Australian in character； and also why such a large number of common Indian forms which extend through Java to Bali； should not have transmitted a single representative to the island further east。
The Mammalia of Timor as well as those of the other islands of the group are exceedingly scanty； with the exception of bats。 These last are tolerably abundant； and no doubt many more remain to be discovered。 Out of fifteen species known from Timor； nine are found also in Java； or the islands west of it； three are Moluccan species； most of which are also found in Australia； and the rest are peculiar to Timor。
The land mammals are only seven in number； as follows： 1。 The common monkey； Macacus cynomolgus； which is found in all the Indo…Malayan islands； and has spread from Java through Bali and Lombock to Timor。 This species is very frequent on the banks of rivers； and may have been conveyed from island to island on trees
