Page images
PDF
EPUB

The Palaearctic affinity of the South Temperate Carabidae may be readily understood, if we bearin mind the great antiquity of the group, and the known long persistence of generic and specific forms of Coleoptera; the facility with which they may be transported to great distances by gales and hurricanes, either on land or over the sea; and, therefore, the probability that suitable stations would be rapidly occupied by species already adapted to them, to the exclusion of those of the adjacent tracts which had been specialised under different conditions. If, for example, we carry ourselves back to the time when the Andes had only risen to half their present altitude, and Patagonia had not emerged from the ocean (an epoch not very remote geologically), we should find nearly all the Carabidae of South America, adapted to a warm, and probably forest-covered country. If, then, a further considerable elevation of the land took place, a large temperate and cold area would be formed, without any suitable insect inhabitants. During the necessarily slow process of elevation, many of the tropical Carabidae would spread upwards, and some would become adapted to the new conditions; while the majority would probably only maintain themselves by continued fresh immigrations. But, as the mountains rose, another set of organisms would make their way along the highest ridges. The abundance and variety of the North Temperate Carabidae, and their complete adaptation to a life on barren plains and rock-strewn mountains, would enable them rapidly to extend into any newly-raised land suitable to them; and thus the whole range of the Rocky Mountains and Andes would obtain a population of northern forms, which would overflow into Patagonia, and there, finding no competitors, would develope into a variety of modified groups. This migration was no doubt effected mainly, during successive glacial epochs, when the mountain-range of the Isthmus of Panama, if moderately increased in height, might become adapted for the passage of northern forms, while storms would often carry insects from peak to peak over intervening forest lowlands or narrow straits of sea. If this is the true explanation, we ought to find no such preponderant northern element in groups which are proportionally less developed in cold and temperate climates. Our further examination will show how far this is the case. Lucanidae.—Only four genera are known in the sub-region. Two are peculiar, Chiasognathus and Streptocerus, the former allied to Tropical American, the latter to Australian genera; the other two genera are exclusively South American. Cetoniidae.—These seem very scarce, only a few species of the Neotropical genus Gymnetis reaching Patagonia. Buprestidae.—These are rather numerous, many very beautiful species being found in Chili. Nineteen genera are represented in South Temperate America, and 5 of these are peculiar to it; 3 others are South American genera; 2 are Australian, and the remainder are wide-spread, but all are found also in Tropical America. The only north-temperate genus is Dicerca, and even this occurs also in the Antilles, Brazil, and Peru. Of the peculiar genera, the largest, Dactylozodes (26 sp.), has one species in South Brazil, and is closely allied to Hyperantha, a genus of Tropical America; Epistomentis is allied to Nascis, an Australian genus; Tyndaris is close to Acmaeodera, a genus of wide range and preferring desert or dry countries. The other two are single species of cosmopolitan affinities. On the whole, therefore, the Buprestidae are unmistakeably Neotropical in character. Longicorns.—Almost the whole of the South Temperate Longicorns inhabit Chili, which is very rich in this beautiful tribe. About 75 genera and 160 species are known, and nearly half of the genera are peculiar. Many of the species are large and handsome, rivalling in beauty those of the most favoured tropical lands. Of the 8 genera of Prionidae 6 are peculiar, but all are allied to Tropical American forms except Microplophorus, which belongs to a group of genera spread over Australia, Europe, and Mexico. The Cerambycidae are much more abundant, and their affinities more interesting. Two (Syllitus and Pseudocephalus) are common to Australia and Chili. Twenty-three are Neotropical; and among these Ibidion, Compsocerus, Callideriphus, Trachyderes, and Xylocharis, are best represented. Twenty are altogether peculiar, but most of them are more or less closely allied to genera inhabiting Tropical America. Some, as the handsome Cheloderus and Owypeltus, have no close allies in any part of the world. Holopterus, though very peculiar, shows most resemblance to a New Zealand insect. Sibylla, Adalbus, and Phantagoderus, have Australian affinities; while Calydon alone shows an affinity for north-temperate forms. One species of the northern genus, Leptura, is said to have been found at Buenos Ayres. The Lamiidae are less abundant. Nine of the genera are Neotropical. Two (Apomecyna and Ecocentrus) are spread over all tropical regions. Ten genera are peculiar; and most of these are related to Neotropical groups or are of doubtful affinities. Only one, Aconopterus, is decidedly allied to a northern genus, Pogonochaerus. It thus appears, that none of the Lamiidae exhibit Australian affinities, although these are a prominent feature in the relations of the Cerambycidae.

It is evident, from the foregoing outline, that the insects of South Temperate America, more than any other class of animals, exhibit a connection with the north temperate regions, yet this connection is only seen in certain groups. In Diurnal Lepidoptera and in Carabidae, the northern element is fully equal to the tropical, or even preponderates over it. We have already suggested an explanation of this fact in the case of the Carabidae, and with the butterflies it is not more difficult. The great mass of Neotropical butterflies are forest species, and have been developed for countless ages in a forest-clad tropical country. The north temperate butterflies, on the other hand, are very largely open-country species, frequenting pastures, mountains, and open plains, and often wandering over an extensive area. These would find, on the higher slopes of mountains, a vegetation and conditions suited to them, and would occupy such stations in less time than would be required to adapt and modify the foresthaunting groups of the American lowlands. In those groups of insects, however, in which the conditions of life are nearly the same as regards both temperate and tropical species, the superior number and variety of the tropical forms has given them the advantage. Thus we find that among the Lucanidae, Buprestidae, and Longicorns, the northern element is hardly perceptible. "Most of these are either purely Neotropical, or allied to Neotropical genera, with the admixture, however, of a decided Australian element. As in the case of the Amphibia and fresh-water fishes, the Australian affinity, as shown by insects, is of two kinds, near and remote. We have a few genera common to the two countries; but more commonly the genera are very distinct, and the affinity is shown by the genera of both countries belonging to a group peculiar to them, but which may be of very great age. In the former case, we must impute some of the resemblance of the two faunas to an actual interchange of forms within the epoch of existing genera—a period of vast and unknown duration in the class of insects; while in the latter case, and perhaps also in many of the former, it seems more in accordance with the whole of the phenomena, to look upon most of the instances as survivals, in the two southern temperate areas, of the relics of groups which had once a much wider distribution. That this is the true explanation, is suggested by the numerous cases of discontinuous and scattered distribution we have had to notice, in which every part of the globe, without exception, is implicated; and there is a reason why these survivals should be rather more frequent in Australia and temperate South America, inasmuch as these two areas agree in the absence of a considerable number of otherwise cosmopolitan vertebrate types, and are also in many respects very similar in climatic and other physical conditions. The preponderating influence of the organic over the physical environment, as taught by Mr. Darwin, leads us to give most weight to the first of the above-mentioned causes; to which we may also impute such undoubted cases of survival of ancient types as the Centetidae of the Antilles and Madagascar—both areas strikingly deficient in the higher vertebrate forms. The probable mode and time of the cross migration between Australia and South America, has been sufficiently discussed in our chapter on the Australian region, when treating of the origin and affinities of the New Zealand fauna.

Islands of the South Temperate Sub-region. These are few, and of not much zoological interest. Tierra del Fuego, although really an island, is divided from the mainland by so narrow a channel that it may be considered as forming part of the continent. The guanaco (Auchenia huanaco) ranges over it, and even to small islands further south. · The Falkland Islands.---These are more important, being situated about 350 miles to the east of Southern Patagonia ; but the intervening sea is shallow, the 100 fathom line of soundings passing outside the islands. We have therefore reason to believe that they have been connected with South America at a not distant epoch; and in agreement with this view we find most of their productions identical, while the few that are peculiar are closely allied to the forms of the mainland.

The only indigenous Mammals are a wolf-like fox (Pseudalopex antarcticus) said to be found nowhere else, but allied to two other species inhabiting Southern Patagonia ; and a species of mouse, probably one of the American genera Hesperomys or Reithrodon.

Sixty-seven species of Birds have been obtained in these islands, but only 18 are land-birds; and even of these 7 are birds of prey, leaving only 11 Passeres. The former are all common South American forms, but one species, Milvago australis, seems peculiar. The 11 Passeres belong to 9 genera, all found on the adjacent mainland. Three, or perhaps four, of the species are however peculiar. These are Phrygilus melanoderus, P. santhogrammus, Cinclodes antarcticus, and Muscisaxicola macloviana. The wading and swimming birds are of little interest, except the penguins, which are greatly developed; no less than eight species being found, five as residents and three as accidental visitors.

No reptiles are known to inhabit these islands.

Juan Fernandez.—This island is situated in the Pacific Ocean, about 400 miles west of Valparaiso in Chili. It is only a few miles in extent, yet it possesses four land-birds, excluding the powerful Accipitres. These are Turdus falklandicus; Ancretes

« EelmineJätka »