21 September 2011

Rani Asmarayani

BIOL 6889Space Seminar

Biogeography and Line: The Malay Archipelago and Wallace’s Line

Introduction

Biogeography has become an important discipline. It integrates the information from the biological and Earth sciences to explain the history and the future of our planet (Riddle & Hafner, 2010). Since its development as a discipline, one of the major focus of the biogeographers is delineating boundary between two adjacent area reflecting different history/organism distribution. Several version biogeographic region systems have been proposed based on either faunal or floral distribution pattern, inferred from the presence/absence of the organism or level of endemicity. Considering different dispersal ability and climate toleranceof each group of taxa, one can easily guess that biogeographic region system inferred from a group of taxa may differ from that inferred from other group of taxa, as seen on faunal and floral biogeographic system.

The Malay Archipelago or Malesiais one of the three most diverse areas in the world, and it provides a good example to examine the biogeographical boundary. It is ordained as a floristic region by van Steenis – and this become the groundwork of Flora Malesiana Project –, and inside the region lay the sharpest, the most famous, and the most discussed biogeographic boundary: Wallace’s Line, which separate Oriental and Australian zoogeographic region. It is obvious here, that the determination of floristic region differs greatly from that of zoogeographic region. The line itself (the Wallace’s Line) has become subject of modification by many zoogeographers. Later, it is found difficult to draw a single line accross those two different zoogeographic region since there is intermediate zone, Wallacea, which has never be a part of both regions.

Recall from “the sharpest” boundary on earth, the bibliography below tries to answer : Does Wallace’s Line act as a boundary for all organism, including plant, in the Malay Archipelago? How does this line influence the distribution and evolutionary patterns of a taxa?

Conclusion

Accompanied by the advance of other disciplines – i. e. plate tectonic theory, paleoclimate reconstruction, molecular genetics, and statistical methods –, researchers can easily explore the biogeographical pattern inferred by various taxa, which in the end can be assembled to a big picture of the biogeography of the Malay Archipelago. A lot of works are still needed though for this area. The biogeographic position of several islands, e.g. Java, has not been well elucidated. Although molecular genetics has been a powerful tool, since it is a useful tool for elucidating historical and evolutionary aspects of the organism dispersal, it has not been explored thoroughly yet.

Annotated Bibliography

  • Cox, C. B. (2001). The biogegraphic regions reconsidered. Journal of Biogeography, 28, 511-523.

This is an argument paper that reviewedand analyzed floral and faunal biogeographic region concepts, from de Candolle to Takhtajan and from Sclater and Wallace, respectively.There are four main conclusions from the paper, i. e.: (1) Criticizing the inconsistencies in using level of endemism methodology in Takhtajan’s floristic kingdom and proposing a revision in the concept; (2) AcceptingWallace’s zoogeographic region concept, but suggesting that it was mammal zoogeographic regions since other animal groups have different dispersal ability; (3) Suggesting that Wallace’s Line concept was not helpful for delimiting Oriental and Australian regions since there is intervening islands area called Wallacea; (4)Suggesting modified names for some floral and faunal biogeographic regions in order to simplify the term. This paper is a good review for reconsidering, as the title, what the biogeographical concept is. The paper is important in the field since the author offered a revised biogeographical concept together with maps. However,although the author pointed out that there were differences between floral and faunal biogeographic regions– due to the dispersal nature of each organismal group and the differences in interest between botanists and zoologists (historical biogeography versus ecological biogeography) –in spite of trying to build a universal concept (i. e. based on plate tectonics)to reconcile them, he kept providing two different revised maps for floral and faunal biogeographic regions. The later left question “shouldn’t biogeographic region concept be applied in all organisms?”

  • Kreft, H. & Jetz, W.(2010). A framework for delineating biogeographical regions based on species distributions. Journal of Biogeography, 37, 2029-2053.

Kreft and Jetz attempted to develop a methodological framework to delineate, analyse and interpret biogeographical regionializations at the global scale based on species distribution using multivariate approach. Using global mammal fauna from IUCN as a model group, they occupied non-metric multidimensional scaling ordination method and nine different hierarchical clustering methods. In general, their grid-assemblage clustering havea broad congruence with Wallace’s six zoogeographic regions. Furthermore their result reaffirm Cox’s (2001) arguments about African realm. The strength of the research lies on their attempt to explore statistical methods rigorously for delineating biogeographic regions, so that the framework is promising to reconcile different biogeographical concepts (i.e. flora and faunal biogeographical concepts). However, as other statistical methods, the reliability of the result depends on the data used. Lack of appropriate, complete data will bias the result. This paper is important in the field for the replicable, quantitative methodological framework the authors built.

  • Riddle, B. R., Dawson, M. N., Hadly, E. A., Hafner, D. J., Hickerson, M. J., Mantooth, S. J., & Yoder, A. D. (2008). The role of molecular genetics in sculpting the future of integrative biogeography. Progress in Physical Geography, 32 (2), 173-202.

The paper reviewed the important role of molecular approaches in shaping the biogeography field nowaday. Molecular phylogenetics has become a powerful tool for biogeographers to reconstruct historical evolution/dispersability or taxa in relation with space and time where they occured. This is an excellent review of the use of molecular genetics in the biogeography. It gave examples to illustrate its purpose, and this is the strength of the paper.

  • Wallace, A. R. (1860). On the zoological geography of the Malay Archipelago. Journal of the Proceedings of Linnean Society (Zoology), 4, 172-184.

This is the landmark, but not the first, study of the biogeographical of the Malay Archipelago. In his famous essay, Wallace described the discontinuity of birds and mammals distribution accross Malay Archipelago. Here, he defined that Lombok Strait to Makasar Strait marked the limits and abruptly separates two zoological regions – Indian and Australian regions – and assigned the Philippine Islands as part of the Indian region. Although relied mostly on the qualitative observation on species distribution (which is the weakness of the paper due to the subjectivity), Wallace has been able to demonstrate and relate the reliability of what later is called Wallace’line, by explaining the evolutionary and geological process underlying the pattern.

  • Simpson, G. G. (1977). Too many lines; The limits of the Oriental and Australian zoogeographic regions. Proceedings of the American Philosophical Society, 121 (2), 107-120.

In this paper, Simpson critically reviewed the seven biogeographical lines assigned in the the Malay Archipelago to mark the boundary of Oriental and Australian zoogeographic regions.In his conclusion, he suggested to (1) keep Huxley’s line and Lydekker’s line as they were clear-cut boundaries of Oriental (Sunda shelf) region and Australian (Sahul shelf) region respectively, and (2) not assign the intervening islands to any region or transitional zone. As an essay, the strength of this paper lies on the considerable aspects of the lines the author reviewed and used to justify his conclusion, i.e. geological background, fossil evidence, and methods to draw the line accros the boundary.This paper has been a good meditation on how different taxonomic group studied can result on different line, the problem which in the recent time begin to be resolved by molecular tools.

  • van Steenis, C. G. G. J.(1950). The delimitation of Malaysia* and its main plant geographical division. In: van Steenis, C. G. G. J. (ed.), Flora Malesiana, Series 1, 1. Noordhoff-Kolff n. v., Djakarta. Pp. 70-75.

This is themajor referenceaddressing Malesiaas a floristic region. Based on literature and herbarium study in Herbarium Bogoriense, Van Steenis applied “generic demarcation knots” method to delimit Malesia – along with three floristic provinces in it, i.e. West Malesia, East Malesia, and South Malesia – and to argue that the demarcation knot in the north part of Malesia correspond to the original Wallace’s Line – than to other lines. In the end, he outlined the contradictions between geology and the phytogeography of Malesia and recommended further reconsideration in the future. The strength of the paper lies on the application of quantitative method to delimit biogeographical region. This paper holds important position until now as the groundwork for Flora Malesiana Project.

* “Malaysia” is the old term for “Malesia”, the term was replaced with “Malesia” to avoid confusion with the nameof the country, “Malaysia”, which gained its independence in 1957.

  • Lohman, D. J., de Bruyn, M., Page, T., von Rintelen, K., Hall, R., Ng, P. K. L., Shih, H. T., Carvalho, G. R., & von Rintelen, T. (2011). Biogeography of the Indo-Australian Archipelago. Annuals of Rev. Ecology, Evolution, Systematics, 42, 205-226.

Lohman et al. presented a synthesized of geological and paleoclimate reconstruction of the archipelago. They also reviewed the recurrent biogeographical patterns inferred from the recent molecular phylogenetic and phylogeographic evidence.Based on the study by Balke et al. (2009) and Jonsson et al. (2008), they showed that Wallace’s Line (or Huxley’s line) and Lydekker’s line are not a rigid boundaries and multiple dispersal events from the beetle genus Rhantus and bird family Campephagidae have been documented. This is the most recent paper of biogeographical study in the Malay Archipelago. It shed new light in the geological and paleoclimate pattern in this area. Furthermore, the incorporation of molecular based studies to infer the biogeographical patterns in the archipelago have been the strength of this paper.

  • Riddle, B. R. & Hafner, D. J. (2010). Integrating pattern with process at biogeographic boundaries: The legacy of Wallace. Ecography, 33, 321-325.

The paper summarized several highlights in the historical focus of biogeographers on boundaries, i. e.Wallace’s Line and Nearctic-Neotropical transition zone. The author also gave a brief illustration on the properties of biogeographic boundary which continue to draw attention of nowaday biogeographers, i. e. reconstructing Earth history, inferring pattern of species biodiversity and processusing molecular approach, and synthesizing the biogeographic pattern. This is a short paper which can give an idea of what has happened and what has been in progress in the field of biogeography of boundaries.

  • Lourie, S. A. & Vincent, A. C. J. (2004). A marine fish follows Wallace’s Line: The phylogeography of the three-spot seahorse (Hippocampus trimaculatus, Syngnathidae, Teleostei) in Southeast Asia. Journal of Biogeography, 31, 1975-1985.

Lourie and Vincent aimed to examine the phylogeographical pattern and to test the potential of two contrasting biogeographical hypotheses, Indian/Pacific Ocean-Basin and Wallace’s Line hypotheses, to explain the distribution of genetic diversity among populations of three-spot seahorse in Southeast Asia. They used cytochrome b gene from 100 samples collected from both sides of Wallace’s Line and from both the Indian and Pacific ocean basins. The result confirmed the Wallace’s Line hypothesis, i. e. two distinct lineages occupied different side of Wallace’s Line. However, separate analysis of samples from east of Wallace’s Line was also consistent with Indian/Pacific Ocean separation. The use of molecular approach to assess the phylogeography pattern is the strength of the paper, despite the way they obtained the samples from fishermen and buyers which could potentially bias the result (the authors have argued that they have carefullfy chosen and interviewed the persons from whom they got the samples). This paper is among the first to focus on marine phylogeography in Southeast Asia.

  • Schulte II, J. A., Melville, J, & Larson, A.(2003). Molecular phylogenetic evidence for ancient divergence of lizard taxa on either side of Wallace’s Line. Proceeding of the Royal Society of London, 270, 579-603.

The paper addressed to estimate divergence time of fauna on either side of Wallace’s Line. Using molecular phylogenetics and dating techniques for two lizard groups, Agamidae subfamily Amphibulorinae and Varanidae-Lanthanotidae, the authorshave been able to demonstrate the ancient fragmentation of the taxa on either side of Wallace’s Line as a result of Gondwanan fragment rifting from the northen margin of Australia or the Indian subcontinent during the Late Jurassic to Early Cretaceous.The taxa chosen for this purpose – i. e. poor aquatic disperser which has distribution on both side of Wallace’s Line –, along with the use of molecular approach and dating techniques – despite critiques on molecular dating – are the strengths of the paper. The paper is among the important ones which shows ancient divergence on either side of Wallace’s Line.

  • van Welzen, P. C. , Slik, J. W. F., & Alahuhta, J.(2005). Plant distribution patterns and plate tectonics in Malesia. Biologiske Skrifter, 55, 199-217.

Van Welzen et al. examined plant distribution patterns and reviewed plate tectonic history which shaped the patterns. Using only Malesian indigenous species published in Flora Malesiana series 1 and the Malesian Orchidaceae, they applied simple statistical methods and PCA to infer the patterns. The study concluded that : (1) Malesia is recognized as a phytogeographical area with three subareas, i. e. Sunda Shelf, Wallacea, and Sahul Shelf (this result is different with previous result by van Steenis); (2) Wallace’s Line is an area of transition, now better known as Wallacea; (3) Plant distribution pattern involved India or Pacific can be explained by plate tectonic history. The issues observed in this paper are partly revisiting the classic paper by van Steenis (1950). Using better data (revised taxonomical species), better tools (various but simple statistical methods), accompanied by recent progress in the field (including molecular phylogenetic data), the paper provides more comprehensive illustration and explanation of the patterns than the classic one. This strength of the paper is at once also describing the importance of the paper in the field. However, as a floristic study which relying the data on the presence and absence of the species, the study still leaves a problem in the biogeography field, that is the incongruency of the floristic biogeographical region and the faunal biogeographical region.

  • van Welzen, P. C., Parnell, J. A. N., & Slik, J. W. F. (2011) Wallace’s Line and plant distributions: Two of three phytogeographical areas and where to group Java? Biological Journal of the Linnean Society, 103, 531-545.

This paper is the next progress of previous paper by van Welzen et al. (2005). Here, the authors addressed whether Wallace’s Line constitutes a major phylogeographical boundary and whether Malesia can be subdivided into phytogeographical areas. They assigned indigenous species published in Flora Malesiana series 1 and the Malesian Orchidaceae on each biogeographical unit (Malay Peninsula, Sumatra, Borneo, so on.) and occupied three different statistical techniques to infer phytogeographical patterns in Malesia. In conclusion, they suggested that there is no sharp east-west boundary in plant distribution in Malesia, and it is better to recognize three phytogeographical areas on the basis of floristic afinities/similarities, those are Sunda Shelf, Wallacea, and Sahul Shelf. Wallacea was further divided to Oriental and Australian ones. This paper assigned more rigorous statistical analyses to infer plant distribution in Malesia and in that way had the more robust result. The paper has its importance in the field for it showed that Wallace’s Line also played an important role in floristic biogeographical region.

  • Aryanti, N. S. & Gradstein, S. R. (2007) Wallace’s Line and the distribution of the liverworts of Sulawesi. Cryptogamie Bryologie, 28 (1), 3-14.

Using herbarium specimens and literature study, Aryanti and Gradstein analysed the geographical and elevational ranges dispersibility of 177 species liverworts. Simply by observe the range of distribution of each species, they conclude that Wallace’s Line played an important role in hampering the dispersibility of the liverworts. They suggested that the limited availability of suitable habitats and reproductive constraints of the eastern Malesian species may have impeded the migration of the liverwort westwards across Wallace’s Line. This is a short paper about distribution pattern of wind-dispersed organism. The simplicity of the research perhaps is the strength of the paper, although it seems like this paper slightly different with “checklist”. It will be better if they can occupy molecular or morphological approaches to strengthen their conclusion. The significance of the paper in the field perhaps lies on the organism they chose, “proving” that wind-dispersed organism also obeysWallace’s Line.

  • Atkins, H., Preston, J., & Cronk, Q. C. B. (2001). A molecular test of Huxley’s Line: Cyrtandra (Gesneriaceae) in Borneo and the Philippines. Biological Journal of the Linnaean Society, 72, 143-159.

The paper examined the biogeography and phylogeny of Cyrtandra (Gesneriaceae) using nuclear ribosomal (ITS) DNA. The authors used 30 species of mostly endemic Cyrtandra from the Sundaland region (Borneo and Peninsular Malaysia) and the Philippines. The strict consensus tree revealed a major division between Sundaland and the Philippines (including Palawan) clades. However, not all of the Palawan species fell in to the Philippines clade, some of them are sister species to Sundaland clade, supporting Huxley’s Line. Atkins et al. suggested ancient vicariance event has occured between Palawan and the Philippines. The use of molecular data to reveal the patterns is the strength of this paper. The paper has contributed to the advance of Gesneriaceae phylogeny and biogeography.

  • McCallum, H. I., Roshier, D. A., Tracey, J. P., Joseph, L., & Heinsohn, R. (2008). Will Wallace’s Line save Australia from avian influenza?. Ecology and Society, 13 (2), 41-56.

This essay described the risk of avian influenza in Australia in relation to Wallace’s Line. There were a lot of highly pathogenic avian influenza incidents in Indonesia, the adjacent country of Australia,which caused more human death than any other countries. Most of the incidents occurred in the west of Wallace’s Line. However, in 2006 there were highly pathogenic avian influenza incidents in West Papua, the closest island to Australia, and this is where the paper began to analyze the risk for Australia. Using bird migratory patterns and avian influenza outbreaks/occurences pattern in Australia, the authors came in to the conclusion that Wallace’s Line probably has protected Australia from the most recent H5N1 avian influenza epizootic. Considering that the pathogen incidents usually occur within poultries, however, the authors has also pointed out the small number of poultries and the increase of vigilance in the government to prevent the widespread of avian influenza since 1997.In relation to the role of Wallace’s Line to protect Australia, the weakness of the paper is that the authors only focused on bird migratory routes in the Australian side of Wallace’s Line. They did not discuss any avian influenza outbreaks in the west side of Wallace’s Line in order to get answer how West Papua could get avian influenza – was that by human or by infection from wild birds – which may potentially give appropriate answer of the role of Wallace’s Line to protect Australia from H5N1 outbreaks. Aside from the weakness, the paper is a good review for the pattern of the disease in Australia. The paper also suggests the future steps to fill the gap of knowledge about the pattern of avian influenza in Australia, which can be a reference for the next step in the field.