Krakatau Group Research Articles

How to go extinct: lessons from the lost plants of Krakatau

AbstractAimFew data sets exist that allow measurement of long‐term extinction and turnover rates for islands of the size of the three main islands of the Krakatau group. We test the reliability of previous estimates of plant species extinction and examine structure within the extinction data.LocationThe data analysed are for the three older Krakatau islands: Rakata, Sertung and Panjang in the Sunda Strait, Indonesia.MethodsOur analysis is based on a comprehensive database incorporating all species records for each island since recolonization began after the 1883 sterilization, plus attributes such as distribution, phylogeny, population status and dispersal mechanism for each species. We employ a combination of univariate and multi‐term analyses in analysing structure, and derive Minimal Adequate Models using binary logistic analyses of variance and covariance. We compare the 1883–1934 data set with the contemporary flora as represented by (1) 1979–83 records (as used in previous analyses) and (2) 1979–94 data (original).ResultsThe improved data for the contemporary flora reduces the number of missing species by one‐third. We show that a variety of estimates of extinction rate can be produced depending on what assumptions are made concerning the status of particular species groups. Structural features in the extinction data persist despite the reduction in overall numbers of losses. Losses relate to: (1) the number of islands on which a species originally occurred, (2) the primary dispersal mode, and (3) the original abundance of a species (e.g. whether it was known to have established a successful resident population, and whether it was in decline or increasing in c. 1930). The ‘best’ descriptive model employs the variables denoted under (3). A high proportion of losses comprised species introduced by people and rare or ephemeral species. Losses of ‘residents’ that had colonized naturally could largely be accounted for by reference to (1) successional loss of habitat and, to a lesser degree, (2) other habitat disturbance or loss.Main conclusionsPrevious analyses, based on a more limited data set, have significantly over‐estimated extinction from the Krakatau flora. Few naturally colonizing and established species have become extinct. The findings indicate that caution is necessary in interpreting ‘headline’ island ecological rates, and in analysing and modelling such data. Examination of structural features of the data appear to be valuable both in providing ecological insights in their own right, and in enabling refinements to estimates of extinction and thus turnover.

Pollinator Limitation of Fig Tree Reproduction on the Island of Anak Krakatau (Indonesia)

Each species of fig tree (Ficus spp., Moraceae) is pollinated by its own unique species of fig wasp (Agaonidae). We examined pollination rates and functional sex-ratios among the fig trees that have colonized the recently formed volcanic island of Anak Krakatau. Four fruiting Ficus species were present. Two of these, F. fistulosa and F. hispida, occurred in small numbers and were receiving sufficient pollinators. In contrast, pollination rates were estimated at 81 percent for F. septica (80 trees fruiting) and only 18 percent for F. fulva (approximately 200 trees fruiting). Both these species had higher pollination rates on the older islands in the Krakatau group. Their functional sex ratios (the proportion of male/female trees bearing fruits) did not differ significantly from 50:50, and there were indications of preferential pollination of female figs. The shortage of pollinators (and therefore mature figs) on Anak Krakatau is likely to have consequences for the frugivorous birds and bats on the island.

An interpretation of the 1883 cataclysmic eruption of Krakatau from geochemical studies on the partial melting of granite

Pumice flow from the 1883 Krakatau eruption significantly differs in both mineral and chemical compositions from any other volcanic rocks or ejecta of the Krakatau group, which belong to the tholeiitic series. Lithic fragments of granitic Rock, discovered in the pumice flow, are similar to West Malayan granitic rocks. No other granitic rock occurs throughout the Krakatau group, therefore, we consider that the granitic fragments came from the underlying complex at depths, where they were captured as foreign materials by the magma.

Post-1883 ash fall on Panjang and Sertung and its ecological impact

This paper describes the post-1883 history of volcanic disturbance to the islands Panjang and Sertung, within the Krakatau group, Indonesia. Historical data are reviewed briefly, together with previous stratigraphic and geochemical data. In 1989 six profiles of soils, ashes and buried soils were described and sampled on each island, along with two on Rakata and one (in Krakatau ash) on Sebesi island. The results of analyses of chemical, physical and particularly of mineral magnetic properties are presented, with the aim of assessing spatial variation in ash fall history across Panjang and Sertung. We take a multivariate approach to analysis of the mineral magnetic data (employing an agglomerative classification), which has proved highly informative as a means of characterising ash fall “events” separated by (in geological terms) very short intervals.

The use of mineral magnetic analyses as an aid in investigating the recent volcanic disturbance history of the Krakatau Islands, Indonesia

The recent disturbance of vegetation on islands within the Krakatau group, Indonesia, by a succession of ash falls from Anak Krakatau, has complicated studies of tropical ecosystem recovery since the major eruption of 1883 provided a 'clean slate'. Mineral magnetic analyses are applied to a series of ash/soil profiles from Sertung, Panjang and Rakata Islands to determine whether the technique can provide a means of stratigraphic correlation of horizons both between sites and between islands (and in particular, correlation and separation of ash layers). The initial results suggest that the technique is sensitive enough to distinguish between particular horizon types (as identified in the field) such as contemporary top-soils, post-1927 ash layers and material of 1883 age. Good agreement is found between the mineral magnetic and traditional geochemical data. The former appear to hold further potential for the separation of (geologically) very close eruptive events from the same magma chamber. The results indicate considerable potential for the approach in the Krakatau context and warrant further investigation of these mineral magnetic properties. If successful, the technique could also find application in other localities where multiple volcanic disturbance events characterize Holocene sediments.

Seismicity of the Sunda Strait: Evidence for crustal extension and volcanological implications

The Sunda Strait is located in the transitional zone between two different modes of subduction: the Java frontal subduction and the Sumatra oblique subduction. This setting implies that the Sunda Strait region is a key to the understanding of the geodynamic processes involved. In order to study the shallow seismicity, a microearthquake survey was carried out in that region. Twelve stations, accurately located by the aim of satellite positionning, recorded about 300 local events in the summer 1984. From this set, 174 shallow earthquakes have been precisely located. The results of this study reveal that the crustal earthquakes in the Sunda Strait area occurs in three main areas: (1) beneath the Krakatau complex, where earthquakes are generated by double‐couples and are of tectonic origin; (2) inside a graben in the western part of the strait; and (3) in a more diffused zone to the south of Sumatra. The individual and composite focal mechanisms from the events inside the strait show an extensional regime. A stress tensor, which have been deduced from the individual focal mechanisms of earthquakes of the Krakatau group shows that the tensional axis is oriented N130°E. This study confirms that the Sunda Strait is in an extensional tectonic regime as a result of the northwestward movement of the Sumatra sliver plate along the Semangko fault zone.

The terrestrial vertebrate fauna of the krakatau islands, sunda strait, 1883-1986

The results of terrestrial vertebrate collecting on the Krakatau Islands, Sunda Strait, during La Trobe University-L.I.P.I. expeditions in 1984, 1985 and 1986 are reported and previous records from the islands are consolidated and reviewed. Since the 1883 eruption of Krakatau, 15 species of terrestrial vertebrates (13 reptiles and 2 mammals) have been recorded from the Krakatau Group. Two of the species records (Crocodylus porosusandCosymbotus platyursareonly incidental but the remaining thirteen species have at some stage established breeding populations on one or more islands. In the first 50 years up to 1933, ten species (eight reptiles and two mammals) reached the islands, eight of which (Hemidactylus frenatus, Lepidodactylus lugubris, Emoia atrocostata, Mabuya multifasciata,Varanus salvator, Python reticulatus, Rattus rattusandRattus tiomanicus) had established breeding populations. Results of collections made over the period 1982-1986 showed that two of the species (L. lugubris and E. atrocostata) with breeding populations in 1933 had become extinct, whereas five new species (Gekko gecko, Gekko monarchus, Hemiphyllodactylus typus, Chrysopelea paradisiandRamphotyphlops braminus) have reached the islands and established breeding populations. Therefore at the end of 100 years, eleven species of terrestrial vertebrates have extant breeding populations on one or more islands in the Krakatau group; two species have become extinct; and two species have incidental records. Significant ecological changes in the development of the present day terrestrial fauna are discussed. These include canopy closure of the forests and continual marine erosion of the coasts that together have eliminated most of the open habitats on Rakata, Sertung and Panjang; heavy ash falls from volcanic eruptions on Anak Krakatau that have periodically disrupted successional stages and habitats on Sertung, Panjang and Anak Krakatau. The dispersal of terrestrial vertebrates in the Sunda Strait is discussed in the light of the heavy boat traffic and the predominant southwest ocean currents. It is concluded that dispersal by human agency on boats is highly significant, seven of the 15 recorded species (46%) being most likely to have reached the islands in this way; and the prevailing southwest flow of water in Sunda Strait makes Sebesi and Sumatra the probable source areas for the eight species most likely to have dispersed on ocean currents by swimming or rafting. Anak Krakatau, the volcanic island that became permanent in Aug. 1930, has three species of terrestrial vertebrates (H. frenatus, V. salvator. andC. paradisi) all of which have established breeding populations on Rakata, Sertung and Panjang. The early arrival ofH. frenatusandV. salvatorand their present abundance on all four islands distinguishes them as the most successful terrestrial vertebrate colonizers of the Krakatau group.

Plant Recolonization and Vegetation Succession on the Krakatau Islands, Indonesia

The development of the vegetation and floras of the Krakatau Islands in the Sunda Straits, Indonesia, since their "sterilization" in 1883 is described. Key features of the post—1883 environment, such as pedogenesis, geomorphology (coastal change), human influence, and recent volcanic activity are detailed, and their possible influence on spatial and temporal patterns in both vegetation and flora is discussed. Field work conducted in 1979, 1983, and 1984 has enabled an assessment of the present state of vegetation development, aided by plot—based sampling and analysis of the arboreal component, employing numerical classification (by TWINSPAN) and ordination (by DCA). The coastal communities were established early and have remained little changed, although the distribution of the various components has changed according to the influence of a dynamic coastal geomorphology. Fifty years after forest closure, the forest of the interiors remain species—poor and composed of typical early—seral species. Rakata was dominated inland by Neonauclea calycina and Ficus pubinervis up to ≈550 m altitude, above which a mossy forest of Ficus spp. and Schefflera polybotrya scrub was recorded. The main inland forest types on Rakata Kecil and Sertung were of young, evenaged stands of Timonius compressicaulis (extensive) and older stands of Dysoxylum gaudichaudianum (often with a T. compressicaulis understory). The principal axes of variation within the data were found to be between extremes of the Rakata forest types, with Sertung and R. Kecil stands remaining undifferentiated until lower levels of the analyses. These patterns were ascribed to a mix of environmental variation (coastal and altitudinal factors), chance variations in colonization, and to volcanic action following the emergence of Anak Krakatau in 1927. Disturbance by volcanism (e.g., in 1930, 1934—1936, 1939, 1952—1953, 1961) has resulted in the deflection of vegetation succession on R. Kecil and Sertung into a different pathway from that followed on Rakata, which has remained unaffected by the activity. On Anak Krakatau, volcanic action has prevented successful colonization away from accreting coastal deposits, and has several times eliminated the entire flora. In addition, the major source of propagules for Anak Krakatau is from within the group, and for these several reasons the new island is shown to be a poor analogue for the early recovery phases of the other islands. Complete floral lists are given for each recorded survey for each island in the group, including data from surveys in 1979, 1982, and 1983. These data have been revised from previous publications on the basis of recent herbarium work and literature searches. The data are analyzed according to several different models: cumulative species totals, species totals for particular combinations of surveys, and totals calculated on the assumption of minimum turnover. The early beach spermatophyte assemblages of Rakata have undergone relatively few losses in comparison to the assemblages of the interior, while within the latter there has been a relatively high proportion of losses among the pioneering pteridophytes. The possession of major habitat types has been identified as critical in determining the shape of the overall colonization curve, through the passive sampling of different source pools. The diversity of the floras of the group as a whole and of Rakata and Anak Krakatau has continued to increase. The curves of species present on Sertung and R. Kecil have levelled and fallen respectively, as a result of the volcanic activity of Anak Krakatau. It is shown that the number of animal—transported species on the Krakatau group has continued to increase over the last 50 yr, and that this accounts for the majority of the increase in the size of the spermatophyte flora. The animal—transported species and the early sea—dispersed species appear to be species—stable groups. Later sea—dispersed species included ephemerals and species of temporary habitats, and have experienced a relatively high proportion of losses. Few beach species that have established on all of the three main islands have subsequently become extinct from the group. The number of pteridophytes on the islands has increased over the last 50 yr, mainly through the addition of forest species. A large proportion of plant species has been found only on Rakata, which samples an upland source pool not represented on the other islands. It is argued that the assumptions of "classical" island biogeography are inappropriate to these data and that the pattern in floral recolonization can best be understood as a successional process involving broad habitat and dispersal mechanism determinants. The implication of these findings is that community dynamics are highly significant in determining rates of immigration, colonization (i.e., successful immigration), and extinction, and that the probabilities of each vary among different groups of species and through time.

Colonization of the Krakatau Islands by Psocoptera (Insecta)

Eighty species of Psocoptera, of 15 families, were collected on the four Krakatau islands in 1982—86, about a century after the 1883 eruption of Krakatau. The most abundant species on the Krakataus (in the families Lepidopsocidae, Ectopsocidae and Peripsocidae, which are also three of the four most diverse families on the Krakatau group) are typical early colonizing forms, but several ecologically more specialized taxa are also present, and some are limited to particular kinds of vegetation. Families characteristic of forest habitats, Pseudocaeciliidae, Myopsocidae and Psocidae, are poorly represented on the Krakataus. The faunas of Rakata and Panjang are markedly more diverse than those known for Sertung or Anak Krakatau, and the first pair of islands, the only one of the six possible pairs to consist wholly of mixed secondary forest, show the greatest faunal similarity. By reference to the presumed source faunas, there is evidence that the most diverse family on the Krakataus, Caeciliidae, (18 species present) is typical of the order as a whole in colonizing ability, whereas the Lepidopsocidae (11), Ectopsocidae (13) and Peripsocidae (11) are relatively good colonizers, and the Pseudocaeciliidae (3), Myopsocidae (2) and Psocidae (4) relatively poor ones. Within the archipelago, the same trends are apparent for the colonization of the young island of Anak Krakatau, which emerged from the sea in 1930. Taking the three other Krakatau islands as the source, the Caeciliidae again show average colonizing ability, and Lepidopsocidae and Ectopsocidae again are relatively good colonizers. The Peripsocidae, however, show up as rather poorer ones in this model. Because species of this family are predominantly bark dwellers their habitat would not be available as early as that for species of the other families, which are found largely on leaf litter and on living leaves. Progressive development of the psocopteran fauna of the archipelago is discussed in relation to vegetational succession.

Antibiotic-resistance patterns of enteric bacteria of wild mammals on the Krakatau islands and west Java, Indonesia.

Apart from feral pigs on Panjang, rats ( Rattus rattus and Rattus tiomanicus ) and bats (various families, genera and species) are the only mammals resident on the Krakatau Islands. The two species of rat occur on separate islands, R. rattus on Rakata and R. tiomanicus on Panjang and Sertung. Both occur on Java. Of the two genera of bats examined, species of Cynopterus were found on Java and all the Krakatau islands, whereas Myotis muricola muricola was detected only on Java and Rakata. The main faecal bacteria of these mammals were shown to be Escherichia coli and species of Klebsiella , Enterobacter and Citrobacter , with other bacteria (e.g. Proteus sp., Pseudomonas sp., Aeromonas sp., Serratia sp., Proteus/ Providenca sp., Morganella sp. and Streptococcus faecalis ) being present in only a minority of individuals Significant differences were noted between the faecal floras of the two rat species. E. coli was always present in R. rattus , but was less frequent in R. tiomanicus (p < 0.05), whereas species of Klebsiella and Citrobacter were less frequent in R. rattus than in R. tiomanicus (p < 0.05). Differences between the faecal floras of the two bat genera were less significant, with the four main faecal bacteria being present in each genus. However, some individual M. muricola muricola yielded S. faeclis, Morganella sp. and Proteus/Providencia sp. whereas species of Cynopterus did not ( p < 0.05). S. faecalis was detected in rats and the bat M. muricola muricola on Java, but not in mammals on the Krakataus. This may be related to the absence of humans and their domesticated animals on the Krakatau islands. Only on Java did rats carry tetracycline-resistant E. coli or tetracycline-resistant species of Klebsiella . This may be related to the widespread use of tetracycline by humans on Java, where tetracycline is available without medical supervision. Isolates of E. coli from rats on Panjang were more resistant to chloramphenicol than were E. coli isolated from rats on the other islands of the Krakatau group, and isolates of Klebsiella from bats on Panjang were more resistant to sulphamethoxazole than were Klebsiella species isolated from bats on Rakata. The reason for faecal bacteria from Panjang mammals being more antibiotic resistant than those from mammals on other islands of the group is unclear, but may be related to differences in diet and vegetation, or the presence of feral pigs on Panjang only.

Geologic significance of granitic fragments found from pumice flow of 1883 eruption at the Krakatau Group, Indonesia

Geologic significance of granitic fragments found from pumice flow of 1883 eruption at the Krakatau Group, Indonesia

Vegetation and succession on the Krakatau Islands, Indonesia

An analysis of the vegetation of four islands of the Krakatau group (Rakata Besar, Rakata Kecil, Sertung and Anak Krakatau), Indonesia, was conducted based on our two expeditions of 1982 in centennial commemoration of the great explosion in 1883. Pioneer communities on lava flow, ash fields, beaches, cliffs and on a scoriaceous slope were quite different from each other. Forest communities were grouped into nine types using Morisita's index of similarity, Cλ(W). Two new forest types which have never been described from Krakatau were identified: Timonius compressicaulis forest and Dysoxylum caulostachyum forest. Successional relations among these community types and the Neonauclea calycina forest were discussed from the viewpoint of seed morphology, dispersal, and the development of juvenile generations in the three types of forest. Dysoxylum forest is the most advanced forest community on the Krakatau Islands. The climax forest is supposed to be a tropical monsoon forest similar to that of the volcanic island Panaitan. A successional scheme is proposed. The invasion times of three forest dominants on the three old islands of Krakatau are compared and it is concluded that the difference in vegetation between these islands, the two Rakatas and Sertung, is determined by the earlier invasion of species which could then extend their cover and build up a forest thus preventing later invaders to establish. We are greatly indebted to Dr Fred Hehuwat, Director of the National Institute of Geology and Mining in Bandung, Mr Peter E. Hehanussa, Chief manager for soil and water resource development in the National Institute of Geology and Mining, Dr Soenartono Adisoemarto, Head of the Museum Zoologicum Bogoriense, Dr Kusuwata Kartawinata, Head of the Herbarium Bogoriense, National Institute of Biology, for their kind cooper-ation and use of their facilities. We also thank the staff of the Indonesian Institute of Sciences for their invaluable help in the field and Dr P. J. Grubb who kindly commented on the manu script. The identification of flowering plants was carried out by T. Partomihardjo, who compared samples with specimens in the Herbarium Bogoriense. The identification was counterchecked by Dr M. Hotta, Associate Professor at the Yoshida College, Kyoto University. Dr C. G. G. J. van Steenis taught us a correct name of a species of Bignoniaceae. Pteridophytes were identified by Dr S. Mitsuda, Dept. of Botany, Faculty of Science, Kyoto University, and bryophytes by Dr T. Seki, Dept. of Botany, Faculty of Science, Hiroshima University.

The Flora of Krakatau

THE eruption of Krakatau, from May 20 to the end of August 1883, which killed the vegetation of the three islands of the Krakatau group and destroyed some two thirds of the island of Krakatau itself, was perhaps the most important volcanic outburst, from the point of view of the biologist, that has occurred in historic times. Its biological importance is, of course, due to the fact that Krakatau is now one of a group of four (formerly three) islands in the middle of the Sunda Strait, Krakatau itself being 40 km. distant from the nearest point of west Java, and the same distance from the nearest point, Varkenshoek, of south-eastern Sumatra. The nearest island to the group is the volcanic Sebesy Island, some 13 km. to the north, where the vegetation was not wholly destroyed. If, as has generally been accepted,, the whole of the vegetation of the Krakatau islands was destroyed, then the study of the gradual reeoloniza-tion recently published by Dr. W. M. Docters van Leeuwen is of unique interest and importance. Krakatau's historic eruption, however, is only one of a series each of which, could it have been studied, would have afforded invaluable information as to methods of plant distribution. Prom the geological evidence, there was originally a single volcanic island in the Straits about 2,000 m. high. This was destroyed, and the three main remaining portions are represented by Krakatau, Verlaten and Lang Islands, surrounding a deep circular sea basin. This eruption was followed by another violent one, and later, by the fusion of the two volcanoes Perbuatan and Danan, the historic island of Bakata or Krakatau, 9 km. long and 5 km. broad, was formed, two thirds of which were erupted and dispersed in 1883. Recently Anak Krakatau has been erupted.