21 September 2011
Rani Asmarayani
BIOL 6889 Space 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 tolerance of 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 Malesia is 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 reviewed and 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) Accepting Wallace’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 have a 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 the major reference addressing Malesia as 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
name of 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 process using 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 authors have 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 obeys Wallace’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), 4156.
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.