Geography | Studies, essays, thesises » Marek-Wolfgang - The krakatau islands as a model area for zoogeographical study a salticidae perspective

A N N A L E S Z O O L O G I C I (Warszawa), 2002, 52(3): 465-474 THE KRAKATAU ISLANDS (INDONESIA) AS A MODEL-AREA FOR ZOOGEOGRAPHICAL STUDY, A SALTICIDAE (ARACHNIDA: ARANEAE) PERSPECTIVE MAREK ¯ABKA1 and WOLFGANG NENTWIG2 1Katedra 2Zoological Zoologii AP, 08-110 Siedlce, Poland, e-mail: zabka@ap.siedlcepl Institute, University of Berne, Baltzerstrasse 3, 3012 Bern, Switzerland, e-mail: wolfgang.nentwig@zosunibech Abstract.— Since 1883-volcanic eruption, 44 salticid species have been recorded on the Krakatau Islands. Of 36 species found during 1984–91 surveys, Anak Krakatau had the richest fauna of 28 species, 22 species were recorded on Rakata, 20 on Panjang and 16 on Sertung Of all the species eight ones were found on all the islands and 13 on only one island The data for Panjang investigated at two time intervals (1883–1931 and 1931–1984/1991), showed a stable number of species (18 and 20 respectively) and a very high changeover rate (13 species gained, 11 lost). Sumatra and

Java were the main sources of colonisation No correlation between area and species diversity was found: despite the smallest area, the salticids of Anak Krakatau appeared the most diverse – partly as the result of the highest biota variety and dynamics. To consider the Krakatau Islands a “good colonisation model” for Salticidae, much effort has to be made standardising collecting methods, selecting appropriate habitats and research time-intervals. Ë Key words.— Island biogeography, Krakatau, Salticidae INTRODUCTION The island life has been the subject of research for over a century and has resulted in hundreds of biogeographical papers, including famous syntheses by MacArthur and Wilson (1967) and Carlquist (1965, 1974). Of all the islands, the archipelago of Krakatau has been one of the most intensely researched, becoming a unique text-book model (MacArthur and Wilson 1967, Thornton 1995, Thornton and New 1988, Thornton et all. 1990, Bush and Whittaker 1991) The studies of the

Krakatau Islands started shortly after the 1883 events and even intensified after the appearance of Anak Krakatau in 1930 (for review see: Thornton and Walsh 1992, Thornton et al. 1992) According to most authors (e.g, Thornton and New 1988, Whittaker et al. 1989, Bush and Whittaker 1991) there are some good reasons to make the Krakatau Islands an excellent example of primary colonisation in the tropics: (1) known starting point of colonisation; (2) little human influence; (3) well defined sources of colonisation (Sumatra and Java); and (4) well documented biological history. We try to discuss all those circumstances from the perspective of jumping spiders and also: (1) analyse colonisation and extinction (changeover) for different biota, island sizes and periods from perturbation; (2) answer whether the equilibrium model proposed by MacArthur and Wilson can be applied to Krakatau jumping spiders; and (3) define the basic methodical requirements necessary for future study. MATERIAL

AND METHODS The spiders were collected by various methods (Tab. 2) during five research expeditions in 1984–1991 (Thornton 1985, 1986, 1987, Thornton and Rosengren 1988, Thornton et al. 1988) Exploited habitats represented various successional stages (Tabs 5, 6) The bulk of Rakata Sertung Anak K. Panjang Not specified males 23 females 33 21 48 juveniles 67 131 443 123 162 539 73 Σ 10 48 6 Σ 4 91 9 8 119 58 45 744 57 954 Table 1. Number of salticid specimens collected on the Krakatau Islands in 1984–91. 466 M. Ż ABKA and W N ENTWIG beating Rakata Sertung 69 71.6 pitfall traps 2.4 hand 2.4 Malaise (aerial?) traps 2.4 8.6 Anak K. Panjang 63.4 69.8 25.4 2.7 6.3 2.6 Table 2. Percentage of specimens collected by selected methods in 1984–91 (for some specimens the data on collecting method were missing). Species 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33.

34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. Artabrus erythrocephalus (C.L Koch) Cosmophasis cyprina (Thorell) Myrmarachne ramosa Badcock Phintella debilis (Thorell) Plexippus paykulli (Audouin) Pseudicius sp. nov Siler semiglaucus (Simon) Zenodorus sp. Bavia sexpunctata (Doleschall) Carrhotus sannio (Thorell) Cosmophasis marxii (Thorell) Cytaea sp. Hasarius adansoni (Audouin) Thyene imperialis (Rossi) Bristowia heterospinosa Reimoser Cosmophasis sp. 1 Cosmophasis sp. 3 Evarcha pococki ¯abka Evarcha sp. nov Hyllus diardi (Walckenaer) Langona bhutanica Prószyñski Marengo sp. nov Menemerus bivittatus (Dufour) Neon sumatranus Logunov Pancorius minutus ¯abka Phlegra pisarskii ¯abka Portia labiata (Thorell) Rhene albigera (C.L Koch) Telamonia caprina (Simon) Thiania bhamoensis Thorell Zenodorus epiphigerus (Simon), comb. n Cocalodes sp. nov Cosmophasis sp. 2 Neon sp. nov Cosmophasis laticlavia (Thorell) Cosmophasis thalassina (C.L Koch) Cosmophasis viridifasciata (Doleschall) Cytaea

guentheri Thorell Portia fimbriata (Doleschall) Pseudicius reiskindi Prószyñski Rhene bufo (Doleschall) Rhene rubigera (Thorell) Thiania demissa (Thorell) Gen. sp Total number of species Species collected in 1984-91 material came from Anak Krakatau (Tab. 1) Altogether, 954 salticid specimens representing 36 species from at least 27 genera were collected (Tab. 3) Of 744 juveniles, only 104 were identifiable. At least 5 species appeared new to science (as the result of limited knowledge of the entire Oriental salticid fauna rather than Krakatau endemism). The species list for different study periods and particular islands is given in Tab. 3 The salticid data R S A 1984–91 1984–91 1984–91 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +? + + + 1984–91 + + + + + + + + + + + + + + + + + P 1931 + + + + + + + +? +? + + + + + + + +? + + + + + + + + + + + + + + + + 22 16 28 18 20 36 Table 3. Salticid

species recorded from the Krakatau Islands R - Rakata, S – Sertung, A – Anak Krakatau, P – Panjang Horizontal lines divide groups of species according to the number of inhabited islands. THE KRAKATAU ISLANDS (INDONESIA) AS A MODEL-AREA FOR ZOOGEOGRAPHICAL STUDY Sumatra/ Other Java distribution Species on the Krakatau Islands 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. Artabrus erythrocephalus (C.L Koch) Cosmophasis cyprina (Thorell) Cosmophasis marxii (Thorell) Zenodorus epiphigerus (Simon), comb. nov Bavia sexpunctata (Doleschall) Cosmophasis laticlavia (Thorell) Cosmophasis thalassina (C.L Koch) Cosmophasis viridifasciata (Doleschall) Hasarius adansoni (Audouin) Hyllus diardi (Walckenaer) Menemerus bivittatus (Dufour) Neon sumatranus Logunov Plexippus paykulli (Audouin) Portia fimbriata (Doleschall) Portia labiata (Thorell) Rhene albigera (C.L Koch) Rhene bufo (Doleschall) Rhene rubigera

(Thorell) Thiania demissa (Thorell) Bristowia heterospinosa Reimoser Carrhotus sannio (Thorell) Cytaea guentheri Thorell Evarcha pococki ¯abka Langona bhutanica Prószyñski Myrmarachne ramosa Badcock Pancorius minutus ¯abka Phintella debilis (Thorell) Phlegra pisarskii ¯abka Pseudicius reiskindi Prószyñski Siler semiglaucus (Simon) Telamonia caprina (Simon) Thiania bhamoensis Thorell Thyene imperialis (Rossi) + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Table 4. Distribution of Salticidae species ever recorded on the Krakatau Islands (species new for science and identified only to the genus level have been excluded). Rakata rain forest grass Casuarina woodland 92 Sertung Anak K. Panjang 55 1.5 24 24 32 34 30 lava 1 shore vegetation 7 Table 5. Percentage of specimens collected from selected habitats in 1984-91 (for some specimens there were no data on habitat). for early stages of colonisation (1883–1931) are

given after Bristowe (1931), Reimoser (1934) and Dammerman (1948). The whole collection is deposited in the Naturhistorisches Museum, Bern, Switzerland. 467 SS GR CAS RF HH L Langona bhutanica Plexippus paykulli Myrmarachne ramosa. Artabrus erythrocephalus Carrhotus sannio Phlegra pisarskii Pseudicius reiskindi Siler semiglaucus Thyene imperialis Thiania bhamoensis Bristowia heterospinosa Cytaea sp. Evarcha pococki Evarcha sp. nov Hasarius adansoni Hyllus diardi Marengo sp. nov Menemerus bivittatus Neon sumatranus Phintella debilis Phintella debilis Portia labiata Rhene albigera Telamonia caprina. Zenodorus epiphigerus + + Species per habitat 9 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 8 11 13 4 NH 5 5 4 3 3 3 3 3 3 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 Table 6. Habitat preferences of selected species in 1984–91 (SS – shore/sand, GR – grassland, CAS – Casuarina woodland, RF – rain forest, HH – human habitations (=

camp site), L – lava, NH – number of habitats from which particular species were found. The horizontal line within the table is arbitrarily proposed for eurytopic species (above) and stenotopic species (below). THE STUDY AREA The Krakatau Islands are situated in the Sunda Strait, some 40 km from Sumatra and Java (Maps 1–3). The islands differ in size, shape, topography, habitat diversity and floristic formations – the parameters influencing immigration and colonisation. On August 26–27th, 1883 the island-volcano Krakatau was destroyed by the gigantic eruption. The island itself and adjacent Sertung and Panjang were sterilised by thick layer of ash, lava and pumice, creating excellent conditions for study on primary colonisation. Today the Krakatau archipelago consists of four islands: Rakata, Panjang, Sertung and Anak Krakatau, the first being the remnant of the ancient pre-1883 volcano and the latter emerging from post-1883 caldera in August 1930. Rakata is the largest (11.5

km2) and the highest (above 800 m) island (Fig. 1) It has the most diverse vegetation Some 330 species (Whittaker et al 1989) constitute various plant communities, depending on altitude 468 M. Ż ABKA and W N ENTWIG SUMATRA N Sunda Strait Sebesti 10° 0 0 BORNEO S U 0° Karkatau Is. 400 km Carita 50 km M A T R A Ujung Kulon Peninsula Java Sea Indian Ocean JAVA JAVA Krakatau 10° 110° 100° 120° Map. 1 Sunda strait showing the Krakatau Islands, after Thonton (1987) spit SERTUNG PANJANG Sandy Foreland N N. Foreland summit of outer cone lava flows E. Foreland 195 m craters ANAK KRAKATAU Pre-1883 lavas Coral Sand Survey control points, Volcanology survey of Indonesia Pre-1883 Krakatau Ravines 0 1 km Bootsmansrots Zwarte Hoek Turtle Beach Cliff Stacks 813 m RAKATA 2 Bouldr Ridge Map. 2 Krakatau Islands in 1985 after Thornton (1987) Owl Bay South Bay Handl’s Bay and soil: from pioneer shore vegetation through grasslands, single Casuarina

trees and Casuarina forest to secondary rainforest. Sertung is the second largest (7.9 km2, 182 m high, 8 km long, 2 km at its widest point). After 1883 eruption the island increased three times as the result of accumulation of 70 m thick pyroclastics layer. The western surface is now dissected by deep gullies while the eastern part is made of deep forested coastal slopes. The main body is covered by tropical monsoon rainforest. Panjang is the second smallest (2.7 km2, 140 m high, 3 km long, 15 km wide). Over 160 plant species are known there, making mostly Casuarina-Dyosoxylum and rainforest associations. Anak Krakatau is the smallest island (2.35 km2, 250 m high, 2 km in diameter). It emerged in 1930 and has erupted many times ever since, the 1952 events being probably sterilising. Despite (thanks?) frequent perturbations, the island has a vari- THE KRAKATAU ISLANDS (INDONESIA) AS A MODEL-AREA FOR ZOOGEOGRAPHICAL STUDY SALTICID DISPERSAL poll caves PANJANG PHPA post N

Pyroclastics pyre 1883 volcanics lava 1960–1981 N cliff in pyroclastics main divide ravine 0 1 bluff km marine cliff summit SERTUNG coral submerged coral 0 1 2 km inner crater rim depression contour N ANAK KRAKATAU contours in metres sandy lowland sandy beach steep forested slope crater floor outer crater rim 500 0 metres vegetation over 90% covr (Anak Krakatau) Map. 3 Anak Krakatau, Panjang and Sertung: topography and habitats, after Thornton (1987) ety of habitats, from pioneer vegetation through grassland to Casuarina forests and rainforests (Figs 2–4). HUMAN INFLUENCE Human influence on Krakatau has been rather limited (Thornton and New 1988). Since 1888 the islands have been visited by scientific expeditions spending some 500 days there, mostly on Rakata and Anak Krakatau. Between August 1896 and January 1897 a small topographical survey team was operating on Panjang and in 1915–1922 a group of people lived on Rakata. In 1928–1931 the Volcanological

Service carried out observations on Panjang. In 1951 a cottage and cultivated garden were found on Sertung, both destroyed by the eruption of Anak Krakatau in 1952. Tourism has been very restricted to short periods of time (Fig. 5) 469 The beaches of the Krakatau Islands are covered with logs, pumice, human debris, seeds, etc. (Figs 6, 7), showing the possibility of rafting – especially for tree trunk and bark dwellers. In addition, floating masses of living vegetation seem an important source of immigrants (Thornton and New 1988). Salticidae are known to constitute only 1%–7.5% of spider aeroplankton (data for other areas) but they can balloon great distances – especially small juveniles and openarea and/or tree-canopy inhabitants (Horner 1975, Salmon and Horner 1977, Decae 1987, Greenstone et al. 1987, Blandenier and Fürst 1998, Patoleta and ¯abka 1999, ¯abka and Nentwig 2000). In Krakatau case only 17 spiders (7 juveniles) were captured by Malaise traps, including adults of

Myrmarachne ramosa, Plexippus paykulli and Siler semiglaucus. As Malaise traps are not selective for aerial trapping, the role of ballooning here is difficult to estimate. For some species anthropodispersal is known to be effective. At least five human habitation dwellers are known to occur in SE Asia, two of them, Plexippus paykulli and Menemerus bivittatus found on the Krakatau Islands. Two other Krakatau species, Langona bhutanica and Siler semiglaucus, are also widely distributed in the region and are likely to be dispersed by man. THE SOURCE OF FAUNA The role of source depends on its size, faunistic richness and distance from destination. Sumatra and Java (425,000 km2 and 132,200 km2, respectively) virtually surround the Krakatau Islands and seem the most natural sources of colonisation. The salticid diversity in Sumatra and Java can be estimated at hundreds of species. For the time being, however, only 121 and 72 species have been recorded for each island respectively (158

species altogether, 35 species in common) (Prószyñski 2002). Of 44 species ever found on Krakatau, 11 were excluded from our analysis as being identified only to the genus level or new to science, with no data on distribution outside Krakatau. Of remaining 33 species, 4 were exclusively known from Sumatra and Java and 15 were additionally found elsewhere in SE Asia (Tab. 4) Fourteen Krakatau species were even more widely distributed in Asia and SW Pacific and, although not formally recorded on Sumatra and Java, they are likely to occur there. 470 M. Ż ABKA and W N ENTWIG Figure 2. The view of Anak Krakatau in 1970 Figure 1. Rakata – the remnant of pre-1883 volcano (taken in 1991 by W. Nentwig) Figure 4. The mixture of rain forest and Casuarina forest on Anak Krakatau (taken in 1991 by W. Nentwig) MEANS OF ARRIVAL AND TURNOVER RATE The distance between source and destination is the main factor influencing means of arrival. The distance acts as selective sieve (Thornton

1996) and is more or less effective, depending on species dispersal power. In majority of cases, however, the actual migration distance is difficult to estimate. Some Krakatau immigrants may Figure 3. Coastal grassland and Casuarina trees on Anak Krakatau (taken in 1991 by W. Nentwig) (at least in theory) have departed from anywhere in Sumatra and/or Java or even from elsewhere in the region, covering much greater distances than 40 kilometres separating Krakatau from Sumatra and Java. The case becomes even more complicated when we consider individual islands of the archipelago as separate sources or destinations (“stepping-stones”). Our data suggested that the exchange of salticids between the islands was THE KRAKATAU ISLANDS (INDONESIA) AS A MODEL-AREA FOR ZOOGEOGRAPHICAL STUDY 471 Figure 5. The groups of tourists approach the Krakatau Islands occasionally (taken in 1991 by W Nentwig) Figure 6. Masses of driftwood and human debris cover the beaches of Krakatau giving the

possibility of rafting (taken in 1991 by W. Nentwig) Figure 7. The seeds collected on the beach of Anak Krakatau, showing possibility of dispersal across the water barrier (taken in 1991 by W Nentwig) limited. Of 36 identifiable species collected in 1984–91 only 8 were recorded on every island and as many as 13 were found only on one island (Tab. 3) Equally, if not more important than physical limitations are species niche requirements. Of 25 species for which the data on habitat were available, as many as 15 were found only in one habitat (Tab. 6) and it is easy to imagine that even those species of Sumatra and Java that “took a risk” of dispersal, have had a very limited chance of landing at the right habitat within Krakatau. As mentioned above, the year 1883 is generally considered the starting point of Krakatau colonisation, except for Anak Krakatau that emerged in 1930 and was (partly?) devastated by subsequent dramatic events (e.g, in 1953, 1972, 1988, 1992, 1993) of which

the 1952eruption was sterilizing (Thornton et all 1994) There are two 50 years long time intervals (1883–1931 and 1931–1984/91) and one island (Panjang) where means of arrival and turnover rate can be analysed. The Panjang salticid list (Tab. 3) comprised 31 species altogether, 18 and 20 of them recorded in 1931 and 1984–91, respectively. Seven species were common for the two analysed periods and as many as 13 species were gained and 11 were lost. Despite the changes in species composition, the number of species for Panjang remained almost stable though considering it the “equilibrium number” (in the meaning proposed by MacArthur and Wilson) would be risky for methodical reasons. The high turnover rate seems the result of rapid succession of biota and AREA AND NUMBER OF SPECIES According to Hamilton et all. (1964), the island’s area accounts for 80–90% of species diversity. Before starting the analysis, we needed to decide whether all the islands of the archipelago were to

be treated as one unit or each individually. Taking the first approach would require islands/archipelagos similar to Krakatau in size, habitats, history, climate and faunistic data to which the Krakatau results might be compared. Because of lack of such models, we considered the islands individually, keeping in mind that each of them had different study records (Tab. 1, 2, 5) Though such an approach brought a risk of overinterpretation, it had already been presented, especially for Rakata and Anak K. (eg, Thornton and Rosengren 1988) According to MacArthur and Wilson (1967) the number of species on the island can be calculated by means of the equation: S = CAz where S is the number of species of a given taxon, A is the island’s area, C is the parameter that depends on taxon and z is the parameter that depends both on taxon and parts of the world and varies between 0.20 and 035 As there was no salticid data for z, we have arbitrarily taken the value of 0.30 [(the same as given for

Ponerine ants by Wilson (in MacArthur and Wilson 1967)]. Then we needed to estimate the value of C from S = CAz-formula. For Anak K. (where A = 235 km2 and S = 28) the value of C = 21.67 On this basis, the theoretical (expectS) for other islands were: 4509 ed) numbers of species (S for Rakata, 40.28 for Sertung and 2919 for Panjang For the largest island of Rakata, where A = 11.5 km2 and S = 22, the value of C = 10.57 On this basis the theS) were: 1965 oretical (expected) numbers of species (S for Sertung, 14.28 for Panjang and 1396 for Anak K Our actual field data had very different values (Fig. 8, 9) Even more striking was the saturation in species: Anak Krakatau had 11.9 species per km2 while Rakata had only 1.91 species per km2 (Fig 10) Habitat diversity can only partly explain those differences. Equally, if not more responsible seem collecting methods and research intensity applied for every island. 35 12 30 10 25 8 20 6 15 4 10 2 5 number of species 14 0 0

Rakata Anak K K. Sertung Panjang area in square km number of species Fig. 8 Island area and number of salticid species found in 1984-91 30 number of species narrow species ecological requirements. As many as 15 salticid species were found only in one habitat and as narrow niche specialists they were more vulnerable to successional or dramatic habitat changes. The Anak Krakatau-case is a good illustration of colonisation dynamics in the tropics. During 39 years (1952–1991) as many as 28 species colonised the island. The “pressure” of surrounding faunas (Sumatra and Java) must have been very important, but equally favourable may have been variety of small-patch habitats maintained as the result of volcanic activity. area in square km M. Ż ABKA and W N ENTWIG 25 20 15 10 5 0 Rakata Sertung Panjang Anak K. K. actual field data expected number of species calculated on the basis of Rak Rakata ata expected number of species calculated on the basis of Anak Krak Krakatau atau

Fig. 9 Actual and theoretical (expected) number of salticid species (1984-91). species/square km 472 10 9 8 7 6 5 4 3 2 1 0 9.36 6.76 1.65 Anak K. K. Panjang Rakata 1.51 Sertung Fig. 10 Species per square km found on particular islands (1984-91) HABITAT HETEROGENEITY AND SUCCESSION Habitat heterogeneity depends on island size, elevation and time since last perturbation. Theoretically, Rakata (the highest, the largest, the most diverse flora, undisturbed since 1883) should have the most diverse salticids. However, as Buckley (1982) pointed out, major and quick habitat changes switch the colonisation process into a sub-mode for each subsequent habitat (especially from open habitats towards closed forests). THE KRAKATAU ISLANDS (INDONESIA) AS A MODEL-AREA FOR ZOOGEOGRAPHICAL STUDY This is why the number of species and turnover rate are much higher for Anak Krakatau than for Rakata. Although the habitats were unequally studied (Tab. 5), we classified the species according

to their habitat requirements (Tab. 6) Only two of them were found in five studied habitats, and as many as 15 were collected in one habitat. This proves that great habitat diversity plays a key-role in supporting rich salticid fauna and increasing saturation of particular island. Again, Anak Krakatau with its open areas, disturbance zones, a number of small scale habitats is the best illustration of this phenomenon. The elevation influences both catching ratio and habitat diversity and is responsible for 2–15% of species occurrence (Hamilton et al. 1964) In the Krakatau-case we had no data for particular elevation zones. Furthermore, the elevation of particular islands did not differ much and habitat diversity depended on other factors rather than the elevation itself. CONCLUSIONS 1. Of 36 salticid species found on the Krakatau Islands in 1984–91, the majority were either widely distributed or pantropical and Sumatra and Java were the most important faunistic sources. 2. The

correlation between species diversity, island size and topography did not emerge from our study because of insufficient data and other co-influencing variables. For the same reason the influence of time since last perturbation proved impossible to verify. 3. The case of Panjang showed a very high turnover rate – a phenomenon typical for small, newly colonised islands. Whether the stable number of species, found within two analysed time intervals, is the “equilibrium number” as proposed by MacArthur and Wilson – it is a matter for further study. 4. The mosaic of biota on Anak K caused by volcanic activity seemed an important factor influencing salticid species number, faunistic diversity and saturation. 5. To consider the Krakatau Islands a “good colonisation model” for Salticidae, much effort has to be made standardising research intensity (the same for every island), collecting methods (e.g, pitfall traps), selecting appropriate habitats (appropriate successional stages for

every island) and research time intervals (e.g, every ten years). ACKNOWLEDGEMENTS Prof. Ian Thornton (La Trobe University, Vic, Australia) and all members of Krakatau expeditions in 1984–91 are acknowledged for collecting material for study. W Nentwig’s visits to Krakatau were supported 473 by the Wander Hochschulstiftung Universität Bern, Switzerland. M ¯abka’s research was supported by Akademia Podlaska, Siedlce, Poland (grants 18/91/S and 512/93/W) and his visit to the University of Berne was possible thanks to the help of the Zoological Institute of the University of Berne and kind hospitality of Prof. W Nentwig and Dr. L Kuhn-Nentwig Prof Jerzy Prószyñski (Warszawa, Poland), Dr Yuri Marusik (Magadan, Russia) and Prof. Wanda Weso³owska (Wroc³aw, Poland) read the manuscript and provided useful comments. Mr Graham Wishart (Gerringong, Australia) corrected the English. REFERENCES Blandenier, G. and P-A Fürst 1998 Ballooning spiders caught by a suction trap in an

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expeditions to the Krakatau Islands, 1984 and 1985: general introduction. Philosophical Transactions of the Royal Society of London, B, 322: 273–316. Thornton, I.WB and D Walsh 1992 Photographic Evidence of Rate of Development of Plant Cover on the Emergent Island Anak Krakatau from 1971 to 1991 and Implications for the Effect of Volcanism. GeoJournal, 282: 249–259 Thornton, I.WB, SA Ward, RA Zann, and TR New 1992 Anak Krakatau – a Colonization Model within a Colonization Model. GeoJournal, 28.2: 271–286 Whittaker, R.J, MB Bush, and K Richards 1989 Plant recolonization and vegetation succession on the Krakatau Islands, Indonesia. Ecological Monographs, 59(2): 59–123 ¯abka, M. and W Nentwig 2000 Salticidae (Arachnida: Araneae) of the Krakatau Islands (Indonesia) – a preliminary approach. Ekológia, 19, Suppl. 3, 293–306 pp Received: April 8 20, 2002 Accepted: June 2, 2002