ZOOGEOGRAPHICAL CHARACTERISTICS OF THE ENTOMOFAUNA OF THE KURIL ISLANDS
SECTION 1. GEOLOGICAL AND FLORAL DEVELOPMENT OF THE KURIL ISLANDS
The entomofauna of any area of the land is closely associated with its vegetation, while the latter is directly dependent upon the geological history of the territory on which it grows. Therefore, in order to make a correct judgment of the process of formation of an entomofauna and its character, one must have a notion of the geological history of the specific region and the history of the development of its vegetation.
The geological history of East Asia and the seas surrounding it have been studied by scientists of various countries, especially intensively in recent decades. However, until now there has been no uniform opinion as to the geological past of this extensive region of the globe, regarding the changes in the outlines of the dry land and the seas surrounding it in this region, although the views of geologists do indeed coincide in relation to particular questions. On this score there exist two main concepts.
According to one of these, advanced by a large group of geologists (Mazarovich, 1951; Udintsev, 1955, 1957; Kanaev, Udintsev, 1961; Panov, 1961; Rudich, 1962; Zhelubovskiy, 1964; Goryachev, 1966; Lebedev, 1968; [the authors of] The Geological Development of the Japanese Islands, 1968, etc.), dry land, which extended during particular time segments to the east of the modern Japanese and Kuril Islands, existed on the site of the modern Sea of Japan and Sea of Okhotsk at the end of the Cretaceous, during the Paleogene, and to some extent, the Neogene. The formation of the depressions of the Seas of Japan and Okhotsk began in the middle of the Tertiary period (the Miocene); of these the former remained a closed body of water for a long time, while the second constituted a gulf of the Pacific Ocean (Figure 59), situated at the site of the Central Kuril Islands. The formation of the island arcs began, accompanied by active volcanism, at the boundary of the Cretaceous and Paleogene, and according to the data of Japanese geologists, in the Miocene. The formation of the Seas of Japan and Okhotsk continued over the Plio-Pleistocene; repeated disruption and restoration of the dry-land connections took place between Japan and Korea in the region of the Tsushima Strait [Tsushima-kaikyo] and between the continent and Sakhalin, in the region of the Tatar Strait. This process was accompanied by a general drop in the continental slope; in particular, the submersion of the dry land of Okhotia, which existed in the central part of the modern Sea of Okhotsk, belongs to this period (Lindberg, 1955, 1970, etc.; Udintsev, 1957; Goryachev, 1966). The outlines of the modern islands and the permanent straits were established definitively only at the end of the Pleistocene-beginning of the Holocene.
An ancient dry-land mass, Beringia, also existed in the northern part of the Pacific Ocean throughout nearly the entire Tertiary and the Pleistocene; Beringia connected the continents of Asia and North America (Krishtofovich, 1932; Hopkins, 1959, and others). Its northern boundary apparently coincided with the boundary of the continental shelf which traverses the Arctic Ocean, while its southern boundary coincided with the chain of the Komandorskiye and the Aleutian Islands (Figure 60). Throughout its existence Beringia repeatedly experienced elevations and submersions, as a result of which the dry-land connection between the continents was sometimes broken and at other times appeared again. In the opinion of I. M. Hopkins (Hopkins, 1959), this connection was finally broken at the beginning of the Holocene as a result of the last transgression of the sea. This concept has been accepted and developed by biogeographers (Krishtofovich, 1932; Shtegman, 1936; VasilÆyev, 1944; Lindberg, 1955, 1970; Kurentsov, 1963a, 1963b; Buks, 1963; Kusakin, 1970, and many others), since it makes it possible to explain the contemporary distribution of many species and closely related forms among the plants and animals on territories which are now separated by marine straits.
According to the second concept, which is being developed by another group of geologists (Kropotkin et al., 1958; Du To,t, 1963; Krauss, 1963; VasilÆkovskiy et al., 1966; VasilÆkovskiy, Khudyakov, 1966; Sychev, 1966, and others), the relative recency and the secondary origination of the Japan and Okhotsk Seas by submersion of hypothetical continental masses formerly in their place, including Okhotia, are denied. The depressions of these seas are considered very ancient depressions which became detached from the Pacific Ocean in the Late Paleozoic. The beginning of the formation of the Japanese island arc and Sakhalin is assigned to the same time period, while the emergence of the Kuril-Kamchatka island arc is hypothetically dated to the end of the Cretaceous-beginning Paleogene (which coincides with the data of the preceding hypothesis). It is hypothesized that dry-land connections between the islands and the continent appeared episodically in the regions of the Tatar and Tsushima Straits no earlier than the Upper Cretaceous epoch, and had the character of relatively narrow bridges. On the whole, the process of so-called continentization of the Earth's crust has taken place on the territory of the marine depressions adjacent to the northeastern part of Asia, i.e., the gradual transformation of the oceanic crust to a continental crust (Sychev, 1966).
Such, schematically, are the views of geologists who have taken opposing positions on the geological history of the northeastern part of the Asian continent.
According to the testimony of paleontological data, the climate in East and North East Asia remained stablely warm and moist during the Cretaceous and the Paleogene; this made it possible for many thermophilous and subtropical plants to grow on this territory (up to Kamchatka, inclusively) - such plants as the wheel-stamen tree, maple, plantain, walnut, beech, hornbeam, hazel, sweet gum, ginkgo, palm, fig, magnolia, sequoia, metasequoia, taxodium, and many others (Sinitsyn, 1965). A certain degree of cooling set in only at the end of the Oligocene and continued to the Miocene; this brought about the partial dropping out of the most highly thermophilous plants, first of all in the flora of the northern regions of North East Asia. In the opinion of A. N. Krishtofovich (1932) and V. B. Sochava (1946), the changes in the composition of the vegetation on the territories of the PriamurÆye and PrimorÆye in the Tertiary and the beginning of the Quaternary were relatively smooth in character. Appreciable changes in climate and a shift in the boundaries of the vegetative zones took place as far back as the Quaternary under the influence of beginning glaciation in the north and northeast of Asia, and through the emergence of the meridionally disposed mountain chains of Sikhot1-AlinÆ, and others, which closed off the internal regions of the continent from the Pacific Ocean. As a result, the moderating action of the oceanic monsoon on the climate of these regions became attenuated; it became drier and more continental on the whole.
With regard to the geological history of the Kuril archipelago, it has not yet been studied conclusively, although a number of studies touching on this question have appeared in recent years (Zhelubovskiy, 1964; Goryachev, 1966; Sergeev, 1966; VasilÆkovskiy, Khudyakov, 1966, and others). It is unanimously recognized by geologists that throughout their existence the Kuril Islands have been on the territory of a geosynclinal region which has experienced constant fluctuations of the Earth's crust. Active tectonic processes, accompanied by mountain formations, associated with intensive volcanism, periodic subsidings of substantial areas of dry land into the waters of the Pacific Ocean and with new elevations, have taken place on a permanent basis in this region. Some attenuation of volcanic activity occurred only at the end of the Paleocene and the Pliocene.
The history of the geological development of the Kuril Islands has been traced on the basis of accumulated scientific data from the Late Cretaceous, when the territory of the Kuril Range was the eastern margin of the continent, on the shore of the Pacific Ocean (Zhelubovskiy, 1964; Goryachev, 1966). Transgression of the sea commenced in the Upper Cretaceous epoch, enclosing the modern Kuril Islands, Kamchatka, Hokkaido, and Sakhalin. Several small chains of volcanic islands, extending in the northeasterly direction, existed at that time in the region of Kamchatka; the largest of these was situated at the site of the present Sredinniy Range. The Greater Kuril Range, found at the boundary of the continent and the ocean and already then rimmed on its outer aspect by a deep-water trough, was its continuation.
Following the transgressions, a substantial elevation, clearly marked on Kamchatka, as well as on Hokkaido and in the southern portion of the Kuril Range (Figure 61), took place in the zone of the Kuril-Kamchatka island arc at the boundary of the Cretaceous and Tertiary periods. There are thus far no direct geological data which make it possible to form an opinion of the paleogeography of the entire Kuril Range at this stage. However, A. V. Goryachev (1966, p. 121) suggests on the basis of indirect information that ôthe central Kamchatka rise extended even farther to the south, all the way to Hokkaido, i.e., dry land existed in the Paleocene on an enormous area of the southern portion of the modern Sea of Okhotsk. The central rise also apparently took in the southern islands of the Lesser Kuril Range ...ö The appearance of the Western Kamchatka trough, which separated Kamchatka and the islands of the Greater Kuril Range from Okhotia, relates approximately to this period (the Eocene).
The period of the Middle Oligocene-Early Miocene was marked by a sharp intensification of volcanism and tectonic movements of the Earth's crust in the region of the Kuril-Kamchatka zone, where active fragmentation of the dry land took place due to the formation of numerous depressions that became marine straits. Nevertheless, dry land which encompassed the eastern part of Kunashir and the territory of the Lesser Kuril Range and which apparently was periodically connected with Hokkaido continued to exist in the south of the Kuril Range.
During the Neogene, right up to the very end of the Pliocene, active volcanic processes, especially intense on its inner aspect, continued within the limits of the Kuril Range. The Greater Kuril Range existed in the form of a garland of volcanic islands which extended between Kamchatka and Hokkaido, and whose outlines varied. According to the hypothesis of A. V. Goryachev, individual islands stood a great distance from one another. But there is no precise information regarding the location and outlines of the islands. It is only reliably known that there was dry land at the site of Iturup in the Middle Miocene, and a dark coniferous taiga flourished. Information on the existence at that time of the Central Kuril Islands is entirely lacking; it is possible that they did not yet exist. A stable elevation was preserved in the region of the Lesser Kuril Range and volcanism was lacking. In the south the Kuril Range was evidently periodically connected with Hokkaido, since marine transgressions and regressions sequentially succeeded one another. The shores, surrounded by a shallow sea at the south and north of the Range, judging by sediments, were markedly incised and had many lagoons. Geologists assume the existence of individual islands or an entire archipelago comprised of raised remnants of the Okhotia which had subsided here, along the western shore of the Greater Range within the limits of the modern Kuril basin; this is suggested by detrital materials of Pliocene age which have drifted onto the Kuril Islands from the Sea of Okhotsk (Goryachev, 1966).
Volcanic activity lessened at the end of the Pliocene in the Kuril-Kamchatka zone, and tectonic movements of the Earth's crust ceased. Smoothing out of the relief took place gradually under the influence of erosion and wear. According to the assertion of Yu. S. Zhelubovskiy (1964, p. 636), ôa more or less even surface of the dry land, divided by several straits into separate large areas extended from Hokkaido to Kamchatka probably by the beginning of the Quaternaryö.
Paleobotanical data which make it possible to make a judgment regarding the environment of the Kuril archipelago in the Tertiary are few in number and relate exclusively to its southern portion. At the same time, the Tertiary flora of Hokkaido, Sakhalin, Kamchatka, and the Komandorskiye Islands, i.e., of the surrounding regions, is quite well known; this offers the possibility of forming a general notion regarding the vegetation of the Kuril Islands and their climate in that period. Just as on Hokkaido, Sakhalin, and Kamchatka, multi-species warmth- and moisture-loving coniferous-broadleaved forests, containing, in addition to deciduous broadleaved species (hornbeam, filbert, zelkova, elm, maple, sweet gum, plantain, etc.), evergreen and taxodium family (Glyptostrobus, Metasequoia, Taxodium) species, complex in composition, apparently flourished in the Paleogene on the Kuril Range. These forests were undoubtedly populated by an equally thermophilous entomofauna. As has already been indicated, the climate was uniformly warm and moist in the Paleogene over the entire continent of Asia.
The climate on the Kuril Range began to change with the onset of cooling in the Late Oligocene-Early Miocene: while remaining moist, it became somewhat cooler overall, and features of latitudinal zonality appeared; this was reflected in the character of the vegetation, which, it must be assumed, became differentiated in various parts of the archipelago. Forests of broadleaved species were gradually transformed into broadleaved-dark coniferous forests. The most thermophilous forms disappeared from their composition; data of spore and pollen analysis of Iturup Middle Miocene sediments (Zhelubovskiy, 1964), which contain mainly the pollen of dark coniferous species (Pinus, Picea, Abies), attest to this.
An interesting schema of change in vegetation on Hokkaido during the Tertiary (Figure 62) is presented in one of the latest works of T. Tanai and K. Huzioka (Tanai, Huzioka, 1967). This schema, it would seem, must reflect similar floristic changes taking place in the Neogene on the Southern Kurils as well.
The definitive formation of the relief and natural conditions of the Kuril archipelago took place in the Quaternary; this was associated with substantial tectonic fluctuations of the Earth's crust and changes in climate in the Kuril-Kamchatka zone in the latest segment of geological history.
Volcanic activity again revived in the Lower Pleistocene; it brought
about the elevation of the Kuril Range, which was especially intense in
the north and south. Faults and fissures appeared in the process, through
which abundant discharges of lava took place, covering the previously leveled
denudation plains. As a result, large volcanic plateaus were formed in
many places. The elevation of the Range continued with some interruptions
until the end of the Pleistocene. Throughout this period, regressions of
the sea commenced at least four times, alternating with transgressions;
this was recorded on the shoreline of the islands in the form of a series
of cyclic1 above-water and underwater marine terraces (Chemekov,
1961; GalÆtsev-Bizyuk, 1968; Kulakov, 1970, etc.). The shallow straits
dried up during the regressions; the southern islands (Kunashir, the Lesser
Kuril Range, and, possibly, the southern part of Iturup) were connected
with one another and with Hokkaido, while the northern islands were connected
with Kamchatka, and the area of the islands themselves increased. In its
turn, Sakhalin was connected with Hokkaido and the continent, and the Japanese
Islands were connected with one another and with the Korean Peninsula (Figure
1Yu. F. Chemekov terms marine terraces which arose simultaneously in large segments of the shores during changes in sea level, cyclic by contrast with local.
A unitary flora and fauna undoubtedly existed on those territories which remained connected for a fairly prolonged period: in the south of the archipelago, a Sakhalin-Southern Kuril-Hokkaido flora and fauna, and in the north, a Northern Kuril-Kamchatka flora and fauna. In addition, plants and animals migrated along dry-land ôbridgesö from the continent. Representatives of a Boreal flora and fauna penetrated the islands through Sakhalin, and a Chinese and oriental flora and fauna through the Korean Peninsula. In particular, the penetration of the mammoth into Hokkaido relates approximately to this time period. Beringian and North American representatives of the plant and animal world penetrated to the north of the archipelago and possibly into its central portion through Kamchatka.
The elevation of the Kuril Range and regressions of the sea during the Pleistocene were accompanied by a gradually ever-intensifying cooling, which led to the formation first of mountain, and then of valley glaciers as well, leaving moraines on the surface of the marine terraces. The glaciation on Iturup and Hokkaido was semi-blanketing [?]; the glaciation was blanketing on the central and northern islands (Chemekov, 1959). Traces of glaciation have not been found on Kunashir and the Lesser Kuril Range; it is entirely probable that there was no glaciation there. The altered climatic conditions could not fail to influence the composition of flora and fauna that had lost a majority of southern forms and taken on a mainly Boreal appearance. But the succession of the vegetative formations and the fauna populating them did not take place suddenly, but to the contrary, very slowly.
At the same time, the constantly active volcanism, the presence of various kinds of thermal springs in the intervals between catastrophic periods of eruptions of particular volcanoes, in combination with the features of the mountainous relief, apparently provided for the existence of local regions with more favorable ecological conditions, as also occurs at the present time as well (see Chapter 4, section 2). Despite the general cooling, thermophilous plants and animals were preserved in such shelters/refuges. This is confirmed by paleontological data of Japanese investigators, according to which thermophilous, and here and there even subtropical, plants and representatives of a cooler climate (Pinus, Picea, Larix, etc.) grew simultaneously in the Pleistocene on Hokkaido and North Honshu. Further, a more cold-loving flora was indigenous to the high mountains and seashores, while a thermophilous flora was indigenous to valley and internal regions of the islands. Judging by plant fossils, the climate in Japan and evidently the south of the Kuril archipelago varied repeatedly during the Pleistocene: temporary periods of warming, the interglacials, would begin in the periods of transgressions against the background of general cooling. The thermophilous flora and fauna would then again begin to spread more widely.
On the central and northern islands, where the glaciation was mainly blanketing, evidently annihilating all vegetation and animals, in the warm periods the sizes of the glaciers decreased and they persisted, it appears, only in mountains. The areas which had subsided, on the other hand, i.e., valleys and terraces, were covered by subalpine vegetation that penetrated there from the north, from Kamchatka and Beringia, and to some extent from the south.
The Kuril Range subsided at the boundary of the Pleistocene and Holocene. A powerful transgression decisively disengaged the islands from one another and from the mainland, following which the ancient dry-land links were no longer restored, despite the new elevation of the Range along its entire extent - the regression and formation of relatively small mountain valley glaciers, mainly on the northern islands - which then followed in the second half of the Holocene.
The relief of the Kuril Islands formed definitively in the Late Quaternary. The large calderas which exist today appeared as the result of explosions with large discharges of pumice: of the Golovnin volcano on Kunashir, the LÆvinaya PastÆ on Iturup, of the Zavaritskiy Volcano on Simushir, etc. Particular volcano islands that had been separated by latest transgression became connected by flat necks and were transformed into large islands of complex structure, like Kunashir and Iturup. Sections of transverse sags of the Earth's crust were began to show in the central section of the archipelago, in the center of the submarine VityazÆ Range. The sagging region was bounded by transverse faults at the site of the deepest straits, the Boussole (2,500 m) and the Krusenstern (1,000-1,300 m). The intensive sagging of this region has continued to the present time (Goryachev, 1966; Sergeev, 1966).
In addition to general elevations and subsidings of the entire range or of large parts of it, geologists (Zhelubovskiy, 1964; Markov, Suyetova, 1965; Goryachev, 1966, etc.) admit the possibility of tectonic movements of a local character; the existence of high marine terraces that does not agree with known eustatic fluctuations of the sea level, points to this. Such a conclusion makes it possible to explain the possibility of the emergence of dry-land links between individual islands independently of general tectonic processes which encompass extensive territories.
The orogenesis of the Kuril archipelago in the modern epoch cannot be considered completed. Tectonic movements of the Earth's crust, expressed in elevations of some sections of the archipelago and the subsidence of others, continue here. Volcanic activity continues to be active. The warming which has set in promotes the migration of plants and animals along the Range in the northerly and southerly directions (Nechaev, 1969; Velizhanin, 1970).
This is the geological history of the Kuril Islands in its general outlines; from this history it can be seen that the island conditions on the territory of the Range were maintained for a prolonged period beginning with the Paleogene. However, because of the incompleteness of the geological chronicle and the paucity of paleontological materials, many factors of the geological development of various sections of the archipelago are not completely clear. In particular, the time of the emergence of the Central Kuril Islands remains in dispute. According to some authors (Zhelubovskiy, 1964; Goryachev, 1966; Sergeev, 1966, etc.), they existed as early as the Miocene; in the opinion of others (Petrushevskiy, 1964, etc.), they have existed from the middle of the Quaternary. Many geologists (Udintsev, 1957; AverÆyanov et al., 1961; Kropotkin and Shakhvarstova, 1965, etc.) and some biogeographers (Velizhanin, 1970) in general deny the possibility of the existence of a dry-land link between Kamchatka and Hokkaido across a solid Kuril ôbridgeö. Let us examine the way in which the zoogeographical character of the Kuril entomofauna agrees with the paleogeographical constructions we have considered.
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