« EelmineJätka »
an outline sketch of the main features of the New Zealand fauna and of its relations with other regions, we may consider what conclusions are fairly deducible from the facts. . As the outlying Norfolk, Chatham, and Lord Howe's Islands, are all inhabited (or have recently been so) by birds of New Zealand type or even identical species, almost incapable of flight, we may infer that these islands show us the former minimum extent of the land-area in which the peculiar forms which characterise the sub-region were developed. If we include the Auckland and Macquarie Islands to the south, we shall have a territory of not much less extent than Australia, and separated from it by perhaps several hundred miles of ocean. Some such ancient land must have existed to allow of the development and specialization of so many peculiar forms of birds, and it probably remained with but slight modifications for a considerable geological period. During all this time it would interchange many of its forms of life with Australia, and there would arise that amount of identity of genera between the two countries which we find to exist. Its extension southwards, perhaps considerably beyond the Macquaries, would bring it within the range of floating ice during colder epochs, and within easy reach of the antarctic, continent during the warm periods; and thus would arise that interchange of genera and species with South America, which forms one of the characteristic features of the natural history of New Zealand.
Captain F. W. Hutton (to whose interesting paper on the Geographical relations of the New Zealand Fauna we are indebted for some of our facts) insists upon the necessity of former land-connections in various directions, and especially of an early southern continental period, twhen New Zealand, Australia, Southern Africa, and South America, were united. Thus he would account for the existence of Struthious birds in all these countries, and for the various other groups of birds, reptiles, fishes, or insects which have no obvious means of traversing the ocean,—and this union must have occurred before mammalia existed in any of these, countries. But such a supposition is quite unnecessary, if we consider that all wingless land-birds and some water-birds (as the Gare-fowl and Steamer"Duck)' are probably cases of abortion of useless' 8tgānis, and that the common ancestors of the various forms of Struthiones may have been capable of a moderate degree 6f flight; or they may have originated in the northern hemisphere; as already explained in Chap. XI. p. 287. The existence of tw8, if not three, distinct families of these birds in New Zealand, proves that the original type was here isolated at a very early date, and being wholly free from the competition of mammalia, became more differentiated than elsewhere. The Hatteria is probably coeval with these early forms, and is the only relic of a whole order of reptiles, which once perhaps ranged far over the globe." Still less does any other form of animal inhabiting New Zealand, require a land connection with distant countries to account for its presence. With the example before us of the Bermudas and Azores, to which a great variety of birds fly annually over vast distances, and even of the recent arrival of new birds in New Zealand and Chatham Island, we may be sure that the ancestors of every New Zealand bird could easily have reached its shores during the countless ages which elapsed while the Dinornis and Apteryx were developing. The wonderful range of some of the existing species of lizards and fresh-water fish, as already given, proves that they too possess means of dispersal which have sufficed to spread them, within a comparatively recent period, over countries separated by thousands of miles of ocean; and the fact that a group like the snakes, so widely distributed and for which the climate of New Zealand is so well adapted, does not exist there, is an additional proof that land connection had nothing to do with the introduction of the existing fauna. We have already (p. 398), discussed in some detail the various modes in which the dispersal of animals in the southern hemisphere has been effected; and in accordance with the principles there established, we conclude, that the New Zealand fauna, living and extinct, demonstrates the existence of an extensive tract of land in the vicinity of Australia, Polynesia, and the Antarctic continent, without having been once actually connected with either of these countries, since the period when mammalia had peopled all the great continents. That event certainly dates back to Secondary, if not to Palaeozoic, times, because so dominant a group must soon have spread over the whole continuous landarea of the globe. We have no reason for believing that birds were an earlier development; and certainly cannot, with any probability, place the origin of the Struthiones before that of Mammals. Causes of the Poverty of Insect-life in New Zealand: its Influence on the Character of the Flora.-The extreme paucity of insects in New Zealand, to which we have already alluded, seems to call for some attempt at explanation. No other country in the world, in which the conditions are equally favourable for insectlife, and which has either been connected with, or is in proximity to, any of the large masses of land, presents a similar phenomenon. The only approach to it is in the Galapagos, and in some of the islands of the Pacific ; and in each of these cases the absence of mammals leads us to infer, that no connection with a continent has ever taken place. Yet the fauna of New Zealand evidently dates back to a remote geological epoch, and it seems strange that an abundance of indigenous insects have not been developed, especially when we consider the vast antiquity that most of the orders and families, and many of the genera, of insects possess (see p. 166), and that they must always have reached the country in greater numbers and variety than any of the higher animals. The undoubted fact that such an indigenous insectfauna has not arisen, would therefore lead us to conclude, that insects find the conditions requisite for their development only in the great continental masses of land, in strict adaptation to, and dependance on, a varied fauna and flora of ever-increasing richness and complexity. A small number of widely-separated forms, introduced into a country where the fauna and flora are alike scanty and unrelated to them, seem to have little tendency to vary and branch out into that vast network of insect-life which enriches all the great continents and their once connected islands. It is a striking confirmation on a large scale, of Mr. Darwin's beautiful theory—that the gay colours of flowers have mostly, or perhaps, wholly been produced, in order to attract insects which aid in their fertilization—that in New Zealand, where insects are so strikingly deficient in variety, the flora should be almost as strikingly deficientingaily-coloured blossoms. Of course there are some exceptions, but as a whole, green, inconspicuous, and imperfect flowers prevail, to an extent not to be equalled in any other part of the globe; and affording a marvellous contrast to the general brilliancy of Australian flowers, combined with the abundance and variety of its insect-life. We must remember, too, that the few gay or conspicuous flowering-plants possessed by New Zealand, are almost all of Australian, South American, or European genera; the peculiar New Zealand or Antarctic genera being almost wholly without conspicuous flowers. In the tropical Galapagos the same thing occurs. Mr. Darwin notices the wretched weedy appearance of the vegetation; and states that it was some time before he discovered that most of the plants were in flower at the time of his visit ! And the insect-life was correspondingly deficient, consisting mainly of a few terrestrial beetles. The poverty of insect-life in New Zealand must, therefore, be a very ancient feature of the country; and it furnishes an additional argument against the theory of land-connection with, or even any near approach to, either Australia, South Africa, or South America. For in that case numbers of winged insects would certainly have entered, and the flowers would then, as in every other part of the world, have been rendered attractive to them by the development of coloured petals; and this character once acquired would long maintain itself, even if the insects had, from some unknown cause, subsequently disappeared. After the preceding paragraphs were written, it occurred to me, that if this reasoning were correct, New Zealand plants ought to be also deficient in scented flowers; because it is a part of the same theory, that the odours of flowers have, like their colours, been developed to attract the insects required to aid in their fertilization. I therefore at once applied to my friend Dr. Hooker, as the highest authority on New Zealand botany; simply asking whether there was any such observed deficiency. His reply was:– “New Zealand plants are remarkably scentless, both in regard to the rarity of scented flowers, of leaves with immersed glands containing essential oils, and of glandular hairs.” There are a few exceptional cases, but these seem even more rare than might be expected, so that the confirmation of theory is very complete. The circumstance that aromatic leaves are also very scarce, suggests the idea that these, too, serve as an attraction to insects. Aromatic plants abound most in arid countries, and on Alpine heights; both localities where winged insects are comparatively scarce, and where it may be necessary to attract them in every possible way. Dr. Hooker also informs, me that since his Introduction to the New Zealand Flora was written, many plants with handsome flowers have been discovered, especially among the Ranunculi, shrubby Veronicas, and herbaceous Compositae. The two former, however, are genera of wide range, which may have originated in New Zealand by the introduction of plants with handsome flowers, which the few indigenous insects would be attracted by, and thus prevent the loss of their gay corollas; so that these discoveries will not much affect the general character of the flora, and its very curious bearing on the past history of the islands through the relations of flowers and insects. In judging of the relation here supposed to exist, it must be remembered, that if the New Zealand insects have been introduced from the surrounding countries by chance immigrations at distant intervals, then, as we go back into the past the insect fauna will become poorer and poorer, and still more inadequate than at present to lead to the development of attractive flowers and odours. This quite harmonizes with the fact of the ancient indigenous flora being so remarkably scentless and inconspicuous, while a few of the more recently introduced genera of plants have retained their floral attractions.