the springtail (hexapoda, collembola) fauna of wrangel island

14
ISSN 0013-8738, Entomological Review, 2010, Vol. 90, No. 5, pp. 571–584. © Pleiades Publishing, Inc., 2010. Original Russian Text © A.B. Babenko, 2010, published in Zoologicheskii Zhurnal, 2010, Vol. 89, No. 7, pp. 804–816. 571 The Springtail (Hexapoda, Collembola) Fauna of Wrangel Island A. B. Babenko Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow 119071, Russia e-mail: [email protected] Received January 25, 2010 Abstract—Analysis of the collembolan fauna of Wrangel Island based on published data and recent sampling was performed. The species richness of springtails on the island (89 species from 41 genera and 12 families) exceeds the levels characteristic of most other insular territories of the Arctic Ocean, except for Greenland and some small islands located within the southern tundra belt. The specificity of the species composition of the springtail fauna on the island depends on a high proportion of species with amphi-Pacific ranges, reflecting its formation within the Beringian Arctic sector. At the same time, the structure of the springtail fauna of the island is rather similar to those of the known tundra faunas of the Siberian sector, with no anomalies being detected. DOI: 10.1134/S0013873810050040 Wrangel Island can be justly regarded as one of the best studied territories in the Arctic, quite comparable with the “international laboratory” of Spitsbergen Archipelago. There are numerous publications devoted to the Wrangel Island biota, starting from the pilot studies of soils and vegetation based on the data of the complex expedition organized by the USSR Academy of Sciences in 1938 (Gorodkov, 1943, 1952a, 1952b, etc.). The good level of knowledge of the island results not only from its protected territory status (i.e., the presence of permanent research staff and relative availability of the territory, at least in the Soviet pe- riod), but also from the specificity of his biota attract- ing specialists in various fields of biology. Despite the southern position of Wrangel Island, lying between 70°47'N and 71°35'N, i.e., at the latitude of eastern Taimyr forest-tundras, the communities of the island are traditionally considered to belong to the arctic tundra subzone (Aleksandrova, 1971, 1977; Yurtsev, 1987). Many plant and animal taxa present on the is- land are characterized by unusually high species diver- sity, distinct endemism (a situation not typically ob- served in the Arctic), obvious genetic connections with the biota of American Beringia, and a consider- able proportion of the Eastern Palaearctic cryo-steppe complex regarded as a “Pleistocene relict.” These and some other specific features of the Wrangel Island biota are traditionally explained by its continuous de- velopment within the vast paleogeographic territory of Beringia, which remained free of ice during the Pleis- tocene and periodically united the territories of South- east Asia, North America, and the exposed continental shelves (Gorodkov, 1952; Petrovskii, 1978; Berman, 1986; Yurtsev, 1986, 1987, 1994; Stishov, 1988, 2004; Khruleva, 2007; Alsos et al., 2009, etc.). This communication presents a review of the re- cently available data on the springtail fauna of Wrangel Island. It was especially interesting to find out if the “anomalous” features of the island’s biota, named above, could be also observed in the fauna of springtails, one of the most typical and numerous groups of Arctic arthropods. There is, in fact, only one special publication devoted to the springtails of this territory (Martynova et al., 1973), which lists 33 spe- cies of this class. There are also some fragmentary descriptions and records of species collected on the island (Martynova, 1969, 1970, 1971; Chelnokov, 1988; Potapov, 1992; Babenko, 1997; Bretfeld, 2000; Potapov and Babenko, 2000; Pomorski, 2001). In addi- tion, the data obtained during a short-term visit within the framework of the Swedish-Russian “Tundra Ecol- ogy—94” expedition in 1994 were included in the Catalogue of Springtails of the Arctic Region (Ba- benko and Fjellberg, 2006). Preparation of this paper was stimulated by the material collected by O.A. Khruleva in 2006 in several important areas of the island, which has essentially changed our estima- tions of its faunistic diversity. I am using this opportu- nity to express my sincere gratitude to O.A. Khruleva

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ISSN 0013-8738, Entomological Review, 2010, Vol. 90, No. 5, pp. 571–584. © Pleiades Publishing, Inc., 2010. Original Russian Text © A.B. Babenko, 2010, published in Zoologicheskii Zhurnal, 2010, Vol. 89, No. 7, pp. 804–816.

571

The Springtail (Hexapoda, Collembola) Fauna of Wrangel Island

A. B. Babenko Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow 119071, Russia

e-mail: [email protected] Received January 25, 2010

Abstract—Analysis of the collembolan fauna of Wrangel Island based on published data and recent sampling was performed. The species richness of springtails on the island (89 species from 41 genera and 12 families) exceeds the levels characteristic of most other insular territories of the Arctic Ocean, except for Greenland and some small islands located within the southern tundra belt. The specificity of the species composition of the springtail fauna on the island depends on a high proportion of species with amphi-Pacific ranges, reflecting its formation within the Beringian Arctic sector. At the same time, the structure of the springtail fauna of the island is rather similar to those of the known tundra faunas of the Siberian sector, with no anomalies being detected. DOI: 10.1134/S0013873810050040

Wrangel Island can be justly regarded as one of the best studied territories in the Arctic, quite comparable with the “international laboratory” of Spitsbergen Archipelago. There are numerous publications devoted to the Wrangel Island biota, starting from the pilot studies of soils and vegetation based on the data of the complex expedition organized by the USSR Academy of Sciences in 1938 (Gorodkov, 1943, 1952a, 1952b, etc.). The good level of knowledge of the island results not only from its protected territory status (i.e., the presence of permanent research staff and relative availability of the territory, at least in the Soviet pe-riod), but also from the specificity of his biota attract-ing specialists in various fields of biology. Despite the southern position of Wrangel Island, lying between 70°47'N and 71°35'N, i.e., at the latitude of eastern Taimyr forest-tundras, the communities of the island are traditionally considered to belong to the arctic tundra subzone (Aleksandrova, 1971, 1977; Yurtsev, 1987). Many plant and animal taxa present on the is-land are characterized by unusually high species diver-sity, distinct endemism (a situation not typically ob-served in the Arctic), obvious genetic connections with the biota of American Beringia, and a consider-able proportion of the Eastern Palaearctic cryo-steppe complex regarded as a “Pleistocene relict.” These and some other specific features of the Wrangel Island biota are traditionally explained by its continuous de-velopment within the vast paleogeographic territory of Beringia, which remained free of ice during the Pleis-

tocene and periodically united the territories of South-east Asia, North America, and the exposed continental shelves (Gorodkov, 1952; Petrovskii, 1978; Berman, 1986; Yurtsev, 1986, 1987, 1994; Stishov, 1988, 2004; Khruleva, 2007; Alsos et al., 2009, etc.).

This communication presents a review of the re-cently available data on the springtail fauna of Wrangel Island. It was especially interesting to find out if the “anomalous” features of the island’s biota, named above, could be also observed in the fauna of springtails, one of the most typical and numerous groups of Arctic arthropods. There is, in fact, only one special publication devoted to the springtails of this territory (Martynova et al., 1973), which lists 33 spe-cies of this class. There are also some fragmentary descriptions and records of species collected on the island (Martynova, 1969, 1970, 1971; Chelnokov, 1988; Potapov, 1992; Babenko, 1997; Bretfeld, 2000; Potapov and Babenko, 2000; Pomorski, 2001). In addi-tion, the data obtained during a short-term visit within the framework of the Swedish-Russian “Tundra Ecol-ogy—94” expedition in 1994 were included in the Catalogue of Springtails of the Arctic Region (Ba-benko and Fjellberg, 2006). Preparation of this paper was stimulated by the material collected by O.A. Khruleva in 2006 in several important areas of the island, which has essentially changed our estima-tions of its faunistic diversity. I am using this opportu-nity to express my sincere gratitude to O.A. Khruleva

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for making it possible for me to process this interest-ing material.

MATERIALS

This communication is based on the published data concerning the fauna of Wrangel Island (see above), collections of 1994 (the lower course of the Mamon-tovaya), and the material collected in 2006 in several areas of the island (the Somnitelnaya Bay area, the upper and middle course of the Somnitelnaya, the middle course of the Mamontovaya, the upper course of the Neizvestnaya, and the middle course of the Neozhidannaya). The main collection areas are shown in Fig. 1. The published data included in the Cata-logue of Springtails of the Arctic Region (Babenko and Fjellberg, 2006) and the author’s long-term collections from various regions of northern Holarctic were used for comparison.

RESULTS

To date, 89 species of springtails have been reliably recorded on Wrangel Island (Table 1). Martynova and co-authors (1973) reported five more species: Hypo-gastrura viatica (Tullberg), Ceratophysella armata (Nicolet), “Isotoma” sp. n.?, Desoria fennica (Reuter),

and Folsomia cf. litsteri Bagnall, whose presence on the island, in my opinion, still remains to be con-firmed. In particular, H. viatica sensu Martynova, hav-ing 7 setae on the dens (Martynova et al., 1973), is probably another species of the viatica group, namely H. sensilis, which commonly occurs in hydromorphic stations of Wrangel Island. The extent and status of the remaining three forms identified to species by Martynova have changed drastically since 1973, so that these names cannot be reliably interpreted now. The presence of Schaefferia czernovi (Martynova)1 is quite probable but still has not been confirmed; the species was mentioned by Stebaeva (1976) with refer-ence to Martynova’s data.

The Wrangel Island fauna still includes 9 species of questionable status, which cannot be precisely identi-fied owing to the available specimens being juveniles (Parisotoma sp., Pygmarrhopalites sp.), taxonomic problems (Oligaphorura cf. schoetti, Xenylla cf. ob-scura, Ballistura sp., Folsomia cf. ozeana, Isotoma cf. variodentata), or clearly insufficient material (Lepido-

_____________ 1 The species was mentioned under an unpublished working name

Hypogastrura (Ceratophysella) duodecimocellata spp. de-cemoculata.

Fig. 1. The main sites of springtail collection on Wrangel Island.

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Table 1. The list of springtail species recorded on Wrangel Island

Mar

tyno

va, 1

969

Mar

tyno

va, 1

970

Mar

tyno

va, 1

971

Mar

tyno

va e

t al.,

197

3

Steb

aeva

, 197

6

Mar

tyno

va, 1

978

Che

lnok

ov, 1

988

Pota

pov,

199

2

Bab

enko

, 199

7

Bre

tfeld

, 200

0

Pota

pov

and

Bab

enko

, 20

00Po

mor

ski,

2001

Bab

enko

and

Fje

llber

g,

2006

Th

is p

aper

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Podura aquatica Linnaeus, 1758 + + Mesaphorura macrochaeta Rusek, 1976 + + Multivesicula dolomitica Rusek, 1982 + + Hymenaphorura palaearctica Pomorski, 2001

+

H. similis (Folsom, 1917) + + Oligaphorura alnus (Fjellberg, 1987) + O. groenlandica (Tullberg, 1876) + + O. cf. schoetti (Lie-Petersen, 1896) + O. ursi (Fjellberg, 1984) + Protaphorura borealis (Martynova, 1973) +* + P. neriensis (Martynova, 1976) + P. octopunctata (Tullberg, 1876) + P. pjasinae (Martynova, 1976) + + Ceratophysella czelnokovi Martynova, 1978 +1 +* + + C. denticulata (Bagnall, 1941) + C. longispina (Tullberg, 1876) +*2 + C. palustris Martynova, 1978 + + Hypogastrura concolor (Carpenter, 1900) + + H. sensilis (Folsom, 1919) + H. trybomi (Schött, 1893) + H. tullbergi (Schäffer, 1900) + + Bonetogastrura nivalis (Martynova, 1973) +* Willemia anophthalma Börner, 1901 + W. denisi Mills, 1932 + W. fjellbergi Potapov, 1994 + W. multilobata Gers et Deharveng, 1985 + W. scandinavica Stach, 1949 + + W. similis Mills, 1934 + + Xenylla cf. obscura Imms, 1912 sensu Ste-baeva et Potapov, 1994

+

Brachystomella parvula (Schäffer, 1896) + + Anurida alpina Agrell, 1939 +*3 + + A. decemoculata Hammer, 1953 + + A. kolymensis Tshelnokov, 1988 + A. martynovae Fjellberg, 1985 + +

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Table 1 (Contd.)

Mar

tyno

va, 1

969

Mar

tyno

va, 1

970

Mar

tyno

va, 1

971

Mar

tyno

va e

t al.,

197

3

Steb

aeva

, 197

6

Mar

tyno

va, 1

978

Che

lnok

ov, 1

988

Pota

pov,

199

2

Bab

enko

, 199

7

Bre

tfeld

, 200

0

Pota

pov

and

Bab

enko

, 20

00Po

mor

ski,

2001

Bab

enko

and

Fje

llber

g,

2006

Th

is p

aper

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 A. polaris (Hammer, 1954) +4 +5 +*6 + + A. similis Fjellberg, 1985 + Micranurida pigmaea Börner, 1901 + Morulina gigantea (Tullberg, 1876) + + M. mackenziana Hammer, 1953 + M. thulensis Hammer, 1953 + Friesea claviseta Axelson, 1900 + F. mirabilis (Tullberg, 1871) + F. quinquespinosa (Wahlgren, 1900) + + Agrenia bidenticulata (Tullberg, 1876) + Anurophorus nitrophilus Potapov, 1997 + Ballistura sp. + B. wangeliensis Martynova, 1973 +* Folsomia atropolaris Potapov et Babenko, 2000

+7 +* +

F. bisetosa Gisin, 1953 + + F. bisetosella Fjellberg, 2005 + F. coeruleogrisea (Hammer, 1938) + +8 + F. cryptophila Potapov et Babenko, 2000 + F. longidens Potapov et Babenko, 2000 +* + F. microchaeta Agrell, 1939 + + F. cf. ozeana Yosii, 1954 +9 + + F. quadrioculata (Tullberg, 1871) + F. regularis Hammer, 1953 + F. taimyrica Martynova, 1973 +* + + Desoria atkasukiensis (Fjellberg, 1978) + + D. blufusata (Fjellberg, 1978) + D. neglecta (Schäffer, 1900) + + D. pjasini (Martynova, 1974) + + + D. propinqua (Axelson, 1902) + + D. tshernovi (Martynova, 1974) +10 + D. sp. group olivacea + Isotoma gorodkovi Martynova, 1970 +* + + I. cf. variodentata Dunger, 1982 + Isotomodella alticola (Bagnall, 1949) +

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Table 1 (Contd.)

Mar

tyno

va, 1

969

Mar

tyno

va, 1

970

Mar

tyno

va, 1

971

Mar

tyno

va e

t al.,

197

3

Steb

aeva

, 197

6

Mar

tyno

va, 1

978

Che

lnok

ov, 1

988

Pota

pov,

199

2

Bab

enko

, 199

7

Bre

tfeld

, 200

0

Pota

pov

and

Bab

enko

, 20

00Po

mor

ski,

2001

Bab

enko

and

Fje

llber

g,

2006

Th

is p

aper

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Isotomurus stuxbergi (Tullberg, 1876) + + Metisotoma grandiceps (Reuter, 1891) + + Pachyotoma crassicauda (Tullberg, 1871) + Parisotoma sp. juv + Pseudisotoma sensibilis (Tullberg, 1876) + + Scutisotoma ananevae (Babenko et Bulav-intsev, 1993)

+ +

Tetracanthella sibirica Deharveng, 1987 +11 +11 + + Vertagopus arcticus Martynova, 1969 +* + V. pseudocinereus Fjellberg, 1975 + Corynothrix borealis Tullberg, 1876 + + Entomobrya bermani Tshelnokov, 1977 + + E. erratica Brown, 1932 + Lepidocyrtus sp. +12 Megalothorax minimus Willem, 1900 + + Sminthurides malmgreni (Tullberg, 1876) + + S. schoetti Axelson, 1903 + + Sphaeridia pumilis (Krausbauer, 1898) + Stenacidia violacea (Reuter, 1881) + Pygmarrhopalites sp. juv + Heterosminthurus borealis Bretfeld et Zöller, 2000

+

Sminthurus orientalis Bretfeld, 2000 +13 +* +

Notes: * Original descriptions of species. 1 Recorded as Ceratophysella sp. (group communis), described later. 2 Described as Ceratophysella arctica sp. n. 3 Described as Anurida tundricola sp. n. 4 Recorded as Anurida remyi Denis, 1947. 5 Recorded as Anurida frigida spp. orientalis, nomen nudum. 6 Described as Anurida wrangelensis sp. n. 7 Recorded as a dark form of Folsomia regularis Hammer, 1953. 8 Recorded as Folsomia alpha Grow et Christiansen, 1977. 9 Recorded as a pale form of Folsomia regularis Hammer, 1953. 10 Recorded as Isotoma olivacea Tullberg, 1971. 11 Recorded as Tetracanthella arctica Cassagnau, 1959. 12 Mentioned as Lepidocyrtus sp. (group violaceus); the species identity is still uncertain. 13 Recorded as Sminthurus viridis (Linné, 1758).

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cyrtus sp., Desoria sp. group olivacea). Although some of them may in the future be described as new to science, their strict association with Wrangel Island is doubtful. In particular, Xenylla cf. obscura was al-ready recorded in central Yakutia (Stebaeva and Pota-pov, 1994) and is quite common in Transbaikalia (Po-

tapov, pers. comm.). Folsomia cf. ozeana and Isotoma cf. variodentata typically occur in arctic landscapes from the Urals to the Chukchi Peninsula. The same species of the genus Ballistura is known from the tun-dras of the Indigirka delta and forest habitats of Ma-gadan Province.

Fig. 2. Cumulative curve of discovery of “new” species on Wrangel Island.

Table 2. Main structural parameters of the springtail fauna of Wrangel Island as compared to those of other northern re-gions

Ratios Region Code

Number of species

found species/ genus

species/ family

genus/ family

Continental tundras of Chukchi Peninsula Ch 141 2.5 8.8 3.5 Taimyr, Ladannakh Lake (southern tundras) T1 121 2.4 7.6 3.2 Putorana Plateau (northern taiga and mountain tundras) P 111 2.1 6.9 3.3 Taimyr, lower course of the Ragozinka (typical tundras) T2 111 2.4 7.4 3.1 Dolgii Island, Pechora Sea (southern tundras) Dol 107 2.4 7.6 3.2 Greenland G 91 2.3 7.6 3.3 Wrangel Island W 89 2.2 7.4 3.4 Taimyr, mouth of the Uboinaya (arctic tundras) T4 83 2.5 7.5 3.0 Taimyr, nothern shore of Taimyr Lake

(northern belt of typical tundras) T3 79 2.0 6.6 3.3

Spitsbergen Archipelago (with nearby islands) Sv 70 1.9 6.4 3.3 Canadian Arctic Archipelago (as a whole) C 59 1.7 5.9 3.4 Novosibirskie Islands (arctic tundras) Ns 51 2.0 4.7 2.3 Novaya Zemlya Archipelago (arctic tundras) NZ 42 1.7 5.1 3.0 Ellesmere Island, Canadian Arctic Archipelago

(arctic tundras) E 42 1.7 4.7 2.8

Devon Island, Canadian Arctic Archipelago (arctic tundras) D 37 1.5 4.1 2.7

Severnaya Zemlya Archipelago (polar deserts) SZ 36 1.6 4.0 2.6 Franz Josef Land (polar deserts) FJL 14 1.4 3.5 2.5 Ellef Ringnes Island, Canadian Arctic Archipelago

(polar deserts) ER 13 1.6 2.6 1.6

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In 1969–2000, 13 new species of springtails were described based on material from Wrangel Island: Protaphorura borealis, Ceratophysella czelnokovi,

C. arctica (= C. longispina), Bonetogastrura nivalis, Anurida tundricola (= A. alpina), A. wrangelensis (= A. polaris), Ballistura wrangeliensis, Folsomia

Fig. 3. Results of cluster analysis of similarity of springtail faunas in various Arctic regions (A) and structure of these faunas at the genus (B) and family (C) level. The analysis was performed with 1—Ics, where Ics is the qualitative (A) or quantitative (B, C) Czekanowski-Sørensen similarity index (Pesenko, 1982). The initial matrices for quantitative indices comprised data on the number of species of a given genus (family) in the fauna of a given region. The region codes correspond to the second column of Table 2.

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atropolaris, F. longidens, F. taimyrica, Isotoma gorodkovi, Vertagopus arcticus, and Sminthurus ori-entalis. This number corresponds to nearly 15% of the known fauna of the island. However, none of these species is endemic to Wrangel Island or at least re-stricted to the Beringian sector.

It is natural that the springtail fauna of Wrangel Is-land is still incompletely studied. Even though collec-

tions have been made in nearly all the most typical plant communities of the island, some types of bio-topes remain insufficiently examined or not examined at all; in particular, no data are available for the littoral stations. On the whole, the territory of the island is not uniformly studied (Fig. 1). The bulk of the material was obtained from the southern (plain) and central (mountain) areas; at the same time, there are no data

Fig. 4. Ordination (scaling) diagrams of similarity of springtail faunas in various Arctic regions (A) and structure of these faunas at the genus (B) and family (C) level. For explanations see Fig. 3.

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on Tundra Akademii (a bogged northern plain where some high-arctic species may occur), and also the eastern and western parts of the island subjected to a noticeable “marine” influence. The cumulative curve showing the history of discovery of “new” species on the island (Fig. 2) also indicates that its fauna is still far from being “exhausted,” the known fauna increas-ing by a third with each consecutive survey. However, considering the available estimations of the Arctic springtail faunas and the potential species pool, one may hardly expect to find many new species on Wrangel Island. In my opinion, the actual springtail fauna of the island comprises about 100 species, which considerably exceeds the values known for most is-lands in the Arctic Ocean (Table 2). A similar level of diversity is characteristic of specific faunas (i.e., fau-nas of small and relatively homogenous regions) at the boundary of typical and arctic tundras in Taimyr, and also of the entire Greenland. Within the southern tun-dra subzone, even small islands may have noticeably richer faunas (see, e.g., Dolgii Island, Table 2).

In the general composition and structure, the spring-tail fauna of Wrangel Island more closely resembles

not those of insular Arctic territories but those of the mainland tundra landscapes; not only of Chukchi Pen-insula, but also of Taimyr (this is the only region where the mainland tundra fauna has been quite com-pletely studied). This was unequivocally demonstrated by cluster analysis and ordination diagrams based on the qualitative index of faunistic similarity (Figs. 3A and 4A) and quantitative parameters of faunistic struc-ture, such as the diversity of particular genera and families (Figs. 3B, 3C, 4B, 4C) and the species/genus, species/family, and genus/family ratios (Table 2). As usual, the greatest number of species was observed in the genus Folsomia (11 species), which appears to be the most diverse in nearly all the humid regions of the Palaearctic. The genus Desoria (7 species) is also well represented; it occupies the second place in the Wrangel Island fauna, which is typical of most Arctic and alpine faunas except the most high-latitude ones (Table 3). The third and fourth places in the fauna of Wrangel Island are shared by two genera, Anurida and Willemia, each represented by 6 species. This might be regarded as one of the specific features of the Wrangel Island fauna. However, an increased diversity of the former genus is generally typical of faunas of the Ber-

Table 3. The most diverse genera of springtails in various regions of the Arctic Region Genera (with number of species)

Greenland Folsomia (13), Mesaphorura (9), Desoria (6) Spitsbergen Archipelago (with nearby islands) Folsomia (9), Desoria (5), Hypogastrura (4), Anurida (4),

Willemia (4), Archisotoma (4) Franz Josef Land (polar deserts) Hypogastrura (4), Folsomia (2) Dolgii Island, Pechora Sea (southern tundras) Folsomia (15), Protaphorura (8), Desoria (7) Novaya Zemlya Archipelago (arctic tundras) Folsomia (7), Hypogastrura (5), Protaphorura (4) Putorana Plateau (northern taiga and mountain tundras) Protaphorura (9), Desoria (8), Folsomia (7) Taimyr, Ladannakh Lake (southern tundras) Desoria (12), Folsomia (10), Protaphorura (10) lower course of the Ragozinka (typical tundras) Folsomia (12), Desoria (11), Protaphorura (9) nothern shore of Taimyr Lake (northern belt

of typical tundras) Folsomia (10), Desoria (8), Protaphorura (8)

mouth of the Uboinaya (arctic tundras) Folsomia (12), Desoria (9), Hypogastrura (7), Protaphorura (7)

Severnaya Zemlya Archipelago (polar deserts) Folsomia (6), Hypogastrura (5), Anurida (2), Willemia (2), Vertagopus (2), Protaphorura (2)

Novosibirskie Islands (arctic tundras) Folsomia (6), Desoria (6), Hypogastrura (5) Wrangel Island Folsomia (11), Desoria (7), Anurida (6), Willemia (6) Continental tundras of Chukchi Peninsula Folsomia (13), Anurida (12), Hypogastrura (10) Canadian Arctic Archipelago (as a whole) Folsomia (9), Hypogastrura (5), Desoria (4), Willemia (4) Devon Island (arctic tundras) Folsomia (7), Hypogastrura (3), Desoria (3), Willemia (3) Ellesmere Island, (arctic tundras) Folsomia (7), Willemia (4), Hypogastrura (3), Desoria (3) Ellef Ringnes Island (polar deserts) Folsomia (3), Hypogastrura (2), Willemia (2), Vertagopus (2)

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ingian sector (Fjellberg, 1985); in particular, the mainland tundras of the Chukchi Peninsula reveal even more species (at least 12). As for the genus Wil-lemia, all or nearly all its species recorded on Wrangel Island are broadly distributed polyzonal forms, which only sporadically occur in arctic landscapes and are usually associated with the best heated and drained patches. The large number of Willemia species re-corded on Wrangel Island may reflect a better level of knowledge of these particular habitats (various cryo-steppe stations), or the prevalence of well-drained soils in the mountain landscapes of the island. Among the specific features of the springtail fauna of the re-gion in question, one should mention a relatively low diversity of the genus Protaphorura, especially no-ticeable by comparison with the rich fauna of Onychi-uridae. Of the 4 species of this genus recorded on Wrangel Island, only P. borealis and P. pjasinae are common, the remaining 2 species being represented by occasional findings. This situation is uncommon for Siberian tundras but appears to be typical of the Euro-pean and American Arctic sectors.

The fauna of any Arctic region includes representa-tives of various zonal groups, from widespread boreal and polyzonal forms to true euarctic ones, whose ranges in plain regions do not extend beyond the boundary of the tundra zone. Wrangel Island is

no exception to this rule, since its fauna includes al-most all the species from the euarctic group of the Taimyr—Severnaya Zemlya region (Babenko, 2003), except Folsomia binoculata which is replaced on the island by several closely related species of group regu-laris. However, all these high-arctic species are scarce, occur sporadically, or are known only from occasional specimens. As a whole, the range of zonal-landscape groups of springtails of Wrangel Island occupies an intermediate position between those of typical and arctic Taimyr tundras (Fig. 5), showing a small but quite noticeable fraction of the hypoarctic complex. The ranges of cenotic groups based on species abun-dance would probably be even more demonstrative, but the corresponding data are not yet available.2 The core of the population of most of the plant communi-ties examined comprises hemiarctic forms, less fre-quently some hypoarctic ones. For example, 7 of the 10 most common species (found in more than 20% of the analyzed samples from Wrangel Island) may be regarded as hemiarctic (Ceratophysella czelnokovi, Protaphorura pjasinae, Morulina gigantea, Folsomia

_____________ 2 Since no quantitative sampling of springtails has been performed

on Wrangel Island, the estimations below are preliminary; they are based on the occurrence of species, rather than on their abun-dance.

Fig. 5. Ratios of the zonal springtail groups in the faunas of Wrangel Island and Taimyr tundras: Ladannakh Lake, southern tundra sub-zone (a), Ragozinka River, typical tundra subzone (b), Uboinaya River mouth, arctic tundra subzone (c). Species groups: polyzonal and boreal (1), hypoarctic (2), hemiarctic (3), and euarctic (4).

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cf. ozeana, Isotoma gorodkovi, Tetracanthella si-birica, and Sminthurus orientalis), two species, as hypoarctic (Folsomia bisetosa and Metisotoma grandiceps), and one species (Willemia similis) is usually considered to be a polyzonal form with a no-ticeable preference for northern territories. It should be noted that a particular species from the Wrangel Island fauna can only conditionally be assigned to a particu-lar zonal group, judging by its latitudinal optimum in another Arctic sector, since quantitative data on the subzonal distribution of springtails are presently avail-able only for Taimyr tundras. In my opinion, the “be-havior” of a particular species in different Arctic re-gions may vary depending on the local conditions; such discrepancies were described in the literature (Chernov, 1975, 1978; Yurtsev, 1987). In addition, since the species lists of Taimyr and Wrangel Island do not overlap completely, the landscape preferences of some springtail species can only be hypothesized based on the total distribution range.

It should be noted that in my opinion, the springtail assemblages of Wrangel Island are more similar in general aspect to the impoverished communities of typical tundras, rather than arctic tundras. This general impression may be confirmed by several significant examples. In particular, soil trap surveys reveal high capture rates of Morulina gigantea and Sminthurus orientalis in the examined communities of Wrangel Island; similar values in Taimyr can be observed only in the southern part of the tundra zone. The same holds true for Folsomia bisetosa and the genus Tetra-canthella (which is represented by different but closely related species): these forms extend into arctic tundras in Taimyr but do not reach such levels of inci-dence and abundance as in the southern parts of the zone and on Wrangel Island. High abundance of En-tomobrya species, a typical feature of the Wrangel Island population, is observed only in the relatively southern areas of Taimyr Peninsula. One more hy-poarctic form typical of the island, Metisotoma grandiceps, is rare in Taimyr already in the typical tundra subzone. There are other similar cases; al-though they are generally not so numerous, they create a distinct “southern” aspect of the Wrangel Island population.

The extreme eastern position within the Palaearctic and the faunistic connections of the region with the American sector are quite adequately reflected in the springtail fauna of Wrangel Island, whose arealogical composition is almost identical to that of the mainland

tundras of Chukchi Peninsula (Fig. 6). Over 40% of the fauna is represented by cosmopolitan and trans-Holarctic forms that can be found in all the tundra regions. The trans-Palaearctic and Eastern Palaearctic species constitute 25%, the latter group being noticea-bly larger. A similar fraction of the fauna belongs to Siberian-American (Beringian and meta-Beringian) forms, which is also typical of tundra regions within the Siberian sector, even though such species are cer-tainly more numerous in the fauna of Wrangel Island and the Northeast in general. In addition, several spe-cies found on Wrangel Island, such as Morulina mackenziana, Entomobrya erratica, Folsomia regu-laris, Anurida similis, and M. thulensis, have mostly American ranges, most of them occurring not only in Alaska but also in the Canadian Arctic. The first two species have not been previously found in the Palae-arctic; in addition, Wrangel Island remains the only Palaearctic locality for F. regularis as well. However, since the inland tundra regions of Chukchi Peninsula are very poorly studied, it would be premature to state that the Palaearctic distribution of these three species is restricted to the southern part of Wrangel Island.

DISCUSSION

In view of the above, it may be concluded that the springtail fauna of Wrangel Island is indeed hardly

Fig. 6. Arealogical structure of springtail faunas of Wrangel Island (A) and mainland tundras of Chukchi Peninsula (B). Ranges: cos-mopolitan (1), trans-Holarctic (2), trans-Palaearctic (3), Eastern Palaearctic (4), Siberian-American (5), Northeast Asian (6), and uncertain (7).

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comparable with the known faunas of large Arctic archipelagoes in species diversity, composition, and structure. However, the opposite would be more sur-prising, since islands of comparable size and position are absent in the Arctic Ocean, except for the south-ernmost parts of Novaya Zemlya and the Canadian Arctic Archipelago, which remain practically unex-plored. The latitudinal position of a territory is natu-rally not the only factor determining its vegetation and fauna, since many macroclimatic parameters, in par-ticular the summer thermal conditions, vary at the same latitude in different Arctic sectors. Still, “plain territories with similar biotic components, positioned at different latitudes, should differ in certain climatic parameters” (Chernov, 1989, p. 52). The latitude dif-ference of 4° between the position of Wrangel Island and the central Novosibirskie Islands (the nearest is-land territory) cannot be insignificant. For example, in the western Taimyr Peninsula all the three tundra sub-zones occur within this latitude range. In my opinion, a higher diversity of the springtail fauna of Wrangel Island, as compared to other island territories of the Arctic, is as natural as, for example, the faunistic dif-ference between the small Dolgii Island (southern tundras) and the northern part of the southern Novaya Zemlya island (Table 2).

Comparison with more or less completely studied specific springtail faunas of Taimyr Peninsula indi-cates that the Wrangel Island fauna has no distinct anomalies. In general, the island fauna is quite typical of the northern part of the tundra zone. It reveals a medium and quite predictable level of diversity and high similarity to the Siberian tundra faunas. There are no endemic forms; the specificity of the species com-position is determined by a significant fraction of spe-cies with amphi-Beringian ranges, which agrees quite well with the meridional position of the island (in my opinion, this is the only specific feature of the spring-tail fauna directly connected with the history of its formation). The proportion of such species in the Wrangel Island fauna is not greater than that in the mainland fauna of Chukchi Peninsula, which is less thoroughly studied. The springtail fauna does not demonstrate “weakening of the taxa associated with hydromorphic habitats,” which is typical of other ar-thropods of Wrangel Island (Khruleva, 2007, 2009). Although it does include numerous representatives of the euedaphic life form (Willemia, Multivesicula, Iso-tomodella), which in the tundra zone prefer the best drained (the warmest and driest) soils, most of the species are hygrophilic forms typical of the tundra

zone. For example, almost all the euarctic forms found on the island are associated with excessively humid habitats, rather than with zonal ones. An increasing “arctic” aspect and reduction of the boreal, polyzonal, and hypoarctic species complexes, observed in the large arthropod fauna (Khruleva, 2007) and flora (Yurtsev, 1986, 1987) of the island, are not so appar-ent in the springtail fauna. On the contrary, the spring-tail fauna of Wrangel Island appears to have the most “southern” aspect of all the known faunas of arctic tundras, which in my opinion quite agrees with its landscape-zonal status.

It should be noted that the position of Wrangel Is-land in the system of zonal subdivision of the Arctic remains quite ambiguous, not only because of the varying approaches and criteria for distinguishing the tundra subzones3 (see, e.g., Stishov, 2004), but also owing to objective factors related to sharp climatic differentiation and complicated orography. The mean July temperatures, one of the commonest parameters correlated with species diversity of many taxa in the Arctic (Chernov, 1989), vary broadly on the island: from 2.4°C at Bay of Rogers (the SE part of the island) to 6.0°C and more in its central regions (Svatkov, 1970; Alfimov, 2007). This range corresponds to the boundary between the typical and arctic tundras of Taimyr Peninsula, which are usually delimited by the July isotherm of 5°C (Chernov and Matveyeva, 1979, 1997). In view of this, it is not surprising that the zonal vegetation of the central parts of Wrangel Island re-sembles the communities of the typical tundra subzone (Yurtsev, 1987; Sekretareva, 1998). The springtail fauna of the island, as a whole, also corresponds to those of typical tundras, rather than the arctic tundras of the Central Siberian sector. Although the specific faunas of Wrangel Island are less diverse than those of the typical tundras of Taimyr, the difference may be explained by incomplete data.

ACKNOWLEDGMENTS The author is very grateful to O.A. Khruleva, the

known expert in the insect fauna of Wrangel Island, for the kindly provided collection material on which this paper has been based. _____________ 3 Aleksandrova (1971, 1977) was the first to assign the plant com-

munities of Wrangel Island to arctic tundras; before this, they had been regarded as polar deserts (Gorodkov, 1943). Using the same criteria in Taimyr, Aleksandrova drew the boundary of the “arctic tundra subregion” along the southern Byrranga foothills, i.e., far to the south of its presently accepted position (Chernov and Matveyeva, 1979).

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The work was financially supported by the Russian Foundation for Basic Research (grants nos. 08-04-00926a, 08-04-00338a), the RAS Presidium programs “Inventory, Functions, and Preservation of Biodiver-sity” and “Origin of the Biosphere and Evolution of Geobotanical Systems,” and the Federal Support Pro-gram for Leading Academic Schools.

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