CHAPTER 6

ZOOGEOGRAPHICAL CHARACTERISTICS OF THE ENTOMOFAUNA OF THE KURIL ISLANDS

SECTION 3. ZOOGEOGRAPHICAL SUBDIVISIONS

Attempts to regionalize the territory of the Kuril archipelago have been undertaken by botanists and zoologists of various specialties since the 1930s. However, a unified opinion has not as yet developed on this score, and the matter remains controversial, although a great deal of factual material has accumulated recently on the chorology of various groups of organisms that permits making an approach to the resolution of the problem of the biogeographical regionalization of the island Range comprehensively, and therefore more objectively.

Based on the geobotanical division of the Holarctic region proposed by a group of biogeographers (Lavrenko, et al., 1952), the Northern and Central Kuril Islands belong to the North Pacific Ocean meadow subregion, while the Southern Kuril Islands, in accordance with the correction of D. P. Vorob'ev (1963), belong to the Far Eastern coniferous-broadleaved forest subregion. Such a division does not elicit fundamental disagreements among the majority of investigators. The question of the finer regionalization of the Kuril Islands remains in dispute.

M. Tatewaki's (Tatewaki, 1933; see Figure 20) and D. P. Vorob'ev's (1963; see Figure 21) disparate schemes of the geobotanical regionalization of the Kuril archipelago have already been cited above. The opinions of zoogeographers in this regard, based on the distribution, most often of different groups of animals, over the Kuril Range also do not coincide in the details. For example, in regionalizing the territory of the south of the Far East and of the Kamchatka Peninsula, A. I. Kurentsov (1959a, 1963b) sets the northern and central islands apart in a special district of the Northern Kuril Islands, belonging to the Kamchatka province of the North Beringian subregion, and sets the southern islands apart in the district of the Southern Kuril Islands, included in the province of Southern Sakhalin and the Southern Kuril Islands. In addition, within the limits of the southern islands, he distinguishes a district of the mountain forests of the Greater Kurils, belonging to the Sakhalin province; from our point of view, this is not entirely acceptable, since vertical zonality is weakly expressed on the Kurils.

Zoologists who have been dealing with the littoral fauna (Kusakin, 1970, and others) assign the Southern Kurils to the Northern Japanese lower boreal province and the central and northern islands to the Upper Boreal Province. O. G. Kusakin (1970, p. 280) emphasizes that "a very important boundary, which fairly clearly divides two biogeographical subdivisions ranking no lower than provincial, crosses the region of Iturup".

A. G. Velizhanin (1970) divides the entire Kuril Range into three "zones" on the basis of an analysis of the vertebrate fauna: the northern continental islands, Paramushir and Shumshu; the ocean islands, the central part of the archipelago form Onekotan to Iturup, inclusively; and the southern continental islands, Kunashir and the Lesser Kuril Range. In their turn, he distinguishes three zoogeographical regions in "the zone of the ocean islands", to which he assigns: 1) the group of islands between the Fourth Kuril and the Krusenstern Straits; 2) all the remaining central islands, including Urup, up to Vries Strait; 3) an independent region, Iturup. A. G. Velizhanin's schema to a substantial degree does not correspond to the distribution of the zoogeographical groups of insects over the archipelago.

The Japanese entomologists Kasiwa (1933), Doi, Uchida (1936), Hori and Tamami (1937)², based mainly on the distribution of lepidopterans, have proposed their own schema of regionalization of the Kuril archipelago. In our view, Hori and Tamami's schema is the most interesting of these; according to it, following M. Tatewaki, the Shikotan-Iturup subregion is distinguished within the Southern Kuril Region, but its northern boundary does not pass through Vries Strait (the Miyabe line), but somewhat further south, evidently across Vetrovoy Neck (this corresponds to the boundary of D. P. Vorob'ev's second subregion). The known commonality of the lepidopteran fauna of Sakhalin, Iturup, and Shikotan, as well as the fact that a number of butterflies which are widely distributed in Japan and on Kunashir are absent on those islands (Sakhalin, Iturup, and Shikotan), was the reason for distinguishing this subregion. This is the basis of the inference regarding a direct link between the enumerated islands (besides Hokkaido and Kunashir) and regarding a dry-land link between Sakhalin with the Northern Kurils and Kamchatka.

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² These studies were published in Japanese and are cited according to S. Kuwayama's paper (Kuwayama, 1967).

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S. Kuwayama (Kuwayama, 1967), guided by an analysis of the Kuril entomofauna as a whole, concluded that the distribution of the insects over the archipelago corresponds completely to the distribution of the vegetation, and fully accepted M. Tatewaki's regionalization schema (Tatewaki, 1933) as suitable for the entomofauna. As we assess the character of the entomofauna and its origin in the various parts of the Kuril Range. as well as the scope of the zoogeographical groups and the population size of the species belonging to one group or another, we are proposing our own schema of regionalization of the Kuril archipelago, which differs somewhat from the preceding (Figure 67).

We assign the Northern and Central Kuril Islands, following the terminology of A. I. Kurentsov, to the Northern Beringian zoogeographical subregion (from our point of view it would be better named the Northwestern Beringian) and the Kamchatka province. We divide this territory into two districts: the Northern Kuril, which includes the northernmost islands up to the Fourth Kuril Strait, with a richer entomofauna of the northern type; the Central Kuril, which encompasses the central part of the archipelago from the Fourth Kuril Strait up to Boussole Strait and is characterized by the extreme impoverishment of its entomofauna, weakly expressed island endemism, and the absence of southern forms.

We add the southern part of the archipelago, including Urup, to the Palaearctic subregion and the Sakhalin-Kuril-Hokkaido province, which is bounded by the limits of Southern Sakhalin, Hokkaido, and the Southern Kurils. We regard the territory of the Southern Kuril Islands as a separate Southern Kuril district, within which we distinguish three regions: 1) the Eastern Hokkaido-Kunashir; 2) the Shikotan-Iturup; 3) the Iturup-Urup.

In terms of the commonality of the natural conditions and the character of the vegetation and the entomofauna, it is advisable to assign, in addition to Kunashir, the easternmost region of Hokkaido, which combines the Siretoko and Nemuro peninsulas as well as the Kushiro River, to the first region. This is a region of broadleaved and coniferous-broadleaved forests, which is distinguished by an extremely rich entomofauna, containing a large number of southern forms and many general island and Kuril proper endemics.

The natural conditions of the second region are similar in many ways to those on Kunashir. However, as indicated above, the vegetation and entomofauna of Shikotan and Iturup are distinguished by a number of features that are characteristic only of these islands. In particular, plants and insects are encountered here that are lacking on Kunashir; the entomofauna is appreciably impoverished by comparison with the latter; the number of island endemics is lower, but on the other hand these are common endemic forms. The features enumerated, in our view, are sufficient to set these islands apart as an independent region, although each of these could in its turn be regarded as a separate subregion on the basis of some features, as D. P. Vorob'ev does.

The last region, the Iturup-Urup, encompassing the northern part of Iturup (the Medvezhiy Peninsula) and Urup, should be regarded as a transitional link between the entomofauna of the southern and central parts of archipelago. The Medvezhiy Peninsula, as has already been noted, was apparently relatively recently attached to Iturup by an aggradation isthmus, but it is closer to Urup in terms of the appearance of the vegetation and character of the fauna than to the central and southern parts of Iturup. Despite the marked impoverishment, representatives of southern zoogeographical groups, especially the Manchurian group, and palaearctic species typically associated with dark coniferous forests are present in the composition of the Urup fauna. We assume that in the future, when the insects of this region are carefully studied, its role as a transitional area in the character of the Kuril entomofauna should become even more evident.