By Jeanmaire Molina
The Philippines is a country of Southeast Asia, with its 7,107 islands
strewn over the Western Pacific Ocean, approximately 13 N of the
equator and 122 E of Greenwich. Its collective land area is about
300,000 sq. km, about the size of the state of Arizona. This island archipelago
is one of the most megadiverse countries in the world, housing over 5%
of the entire world’s flora in an area not even 1% of the
world’s total. An estimated 10,000 to 11,000
species of plants are believed to occur in the Philippines and likely many more if the tropical forests were
fully explored and documented. Over half of the named plants are
endemic. This high level of endemism is also present in the animals.
Forty-four percent of its vertebrate species and almost 70% of its
insects are also found nowhere else in the world (Catibog-Sinha and
Heaney 2006). Among the world’s 25 top biological hotspots the
Philippines ranks second in the number of species per square kilometer,
thus the endemic species are concentrated in exceptionally small areas
(Myers et al. 2000). Only 7% of its old growth closed-canopy forests
remain from over 60% in 1945 (Heaney et al. 2004). Therefore, these
species are under extremely high threats for extinction. As with any
other developing nation, poverty, overpopulation, ignorance, and
political corruption continue to threaten the remaining biological
riches of this country.
With so many islands, the Philippines surpasses Hawaii and the
Galapagos in species biodiversity and endemism, and would be the
perfect system to understand why it is a cauldron of evolution. In
fact, the Philippines has been described as tenfold more diverse than
Galapagos (Heaney and Regalado 1998). As predicted by Wilson and
MacArthur’s (1967) theory of island biogeography, different
island sizes, ages and distance from mainland Asia have influenced
colonization, extinction, and diversification rates of Philippine
biota. These island features coupled with their individual geological
histories throughout the Cenozoic may hold the answer as to why the
Philippines is one of the world’s most biodiverse regions.
Ancient geological history of the Philippine archipelago
drifted northward and began to collide with Asia, tectonic pressure
caused parts of the Pacific seafloor to uplift, producing volcanoes
that gave rise to the Philippine islands. Sometime in the
mid-Oligocene, about 30 mya, the Philippines was starting to take shape
with the development of three major geological blocks (Fig. 1A). The
first unit, which now comprise modern day Palawan and Mindoro and other
smaller islands, rifted from the Asian continental shelf, south of the current location of
Taiwan. At about the same time, hundreds of kilometers southeast
of its present-day location, proto-Luzon, which began as a string of
small volcanic islands developing beneath a shallow sea, was moving
northwest. Further southeast of proto-Luzon, the islands of the Visayas
and Mindanao were borne out of the continued subduction of the
converging plates in the Pacific, and were also migrating northwest.
Throughout the Cenozoic, these major geological units were approaching
one another, but it was only in the Miocene that they began to emerge
above sea level (Fig. 1B). About 10 mya (Fig. 1C) Mindoro was uplifted
and large land areas were already exposed for the two other geological
units. Starting in the Pliocene, 5 mya (Fig. 1D), Palawan emerged,
while other smaller islands and peninsulas such as Bicol, Camiguin and
Sibuyan, and the Sulu islands only surfaced much later (Hall 1998;
Heaney and Regalado 1998; Steppan et al. 2003).
The 7000+ islands of the Philippines had never been connected to
other Asian landmass, except for Palawan, which became contiguous with
Borneo when sea level dropped repeatedly during the
Pleistocene, accounting for Palawan’s biotic similarity to
the former. The isolation of the Philippines from the rest of Asia
allowed it to
develop its unique flora and fauna, thus explaining its staggering
levels of endemism. Moreover, many species are not only endemic to the
Philippines but unique to individual Philippine islands. Other islands,
like Negros and Panay, share faunal species which surprisingly are
different from those on other adjacent Visayan islands such as Leyte
and Samar, whose fauna are, in turn, more similar to those of Mindanao.
Masbate’s fauna are also more related to Negros and Panay’s
than they are to the more proximal Luzon. These patterns were observed
in many vertebrates including birds (Peterson et al. 2000), amphibians
(Evans et al. 2003), mammals (Heaney and Regalado 1998; Steppan et al
2003; Roberts 2006; Esselstyn and Brown 2009), reptiles (McGuire &
Heang 2001), and fishes (Carpenter and Springer 2005).
Fig. 1. Postulated distribution of land and sea in Southeast Asia in
the Cenozoic. A. 30 mya. B. 20 mya. C. 10 mya. D. 5 mya. Figures from
Philippine Pleistocene Islands
Though the country’s ancient
geology, beginning at least in the Oligocene, had undoubtedly shaped
Philippine biodiversity, biotic similarities of certain island groups
only make sense in the light of the country’s Pleistocene
history. About 2 mya, water evaporating from the oceans formed very
thick glaciers that blanketed temperate regions for thousands of years,
thereby resulting in global sea levels 120 m below present. This
allowed certain islands of the Philippines to coalesce, forming
Pleistocene island groups (Heaney and Regalado 1998; Fig. 2), but after
some time, the glaciers melted thereby disconnecting these islands.
This cycle went on repeatedly several times with the last glacial
episode culminating 12,000 yrs ago and could explain the biogeographic
patterns seen in many Philippine vertebrate taxa (Catibog-Sinha and
During glacial events, five major Pleistocene island groups became
prominent: Greater Luzon (composed of Luzon, Catanduanes, Marinduque
and Polillo); Greater Mindanao (Mindanao, Bohol, Leyte, Samar,
Basilan); Greater Negros-Panay (Cebu, Masbate, Negros, Panay); Greater
Sulu (Tawi-Tawi, Sulu); and Greater Palawan. Except for Palawan, these
Pleistocene island groups have never been connected to one another nor
to the Asian mainland. The islands of Mindoro, Sibuyan, Camiguin, and
Siquijor have also remained isolated from any other island (Heaney and
Regalado 1998; Catibog-Sinha and Heaney 2006; Fig. 2). Thus, it is not
surprising that each of these Pleistocene islands harbors unique set of
species. For example, 76% of the non-flying mammals in Greater Luzon do
not exist anywhere else, and the number for Greater Mindanao is even
higher at 79% (Catibog-Sinha and Heaney 2006). Even the tiny, less than
500 sq. km and solitary island of Sibuyan, has its own impressive array
of endemic species, in spite being only a few kilometers away from
It would seem reasonable to think that the recurring coalescence and
fragmentation of certain islands during the Pleistocene were
responsible for generating much of Philippine biodiversity, i.e. the
Pleistocene speciation hypothesis (Steppan et al. 2003). However, this
was not the case, at least for the species of a Philippine endemic
rodent, in which the timing of speciations occurred pre-Pleistocene,
during the Pliocene (Steppan et al 2003; Jansa et al. 2006). The same
story was reported for an endemic Philippine fruit bat, whose
genetically different populations resulted from Pliocene
diversifications (Roberts 2006). Nonetheless, for both taxa,
monophyletic groups are generally confined within the boundaries of
each Pleistocene island. This has led Heaney et al. (2005) to conclude
that distributional patterns of non-vagile mammal species are generally
consistent with the expectations of Pleistocene geography, and that the
latter may be predictive of the biogeography of other species in
However, not all Philippine species obey the Pleistocene geography
model and show complex diversification patterns; many even exemplify
cryptic speciations. For many Philippine bird species, allopatric
differentiations occurred after colonization of different islands
(Oliveros and Moyle 2010; Jones and Kennedy 2008). This was also
observed in Philippine shrews (Esselstyn et al. 2009) and skinks (Siler
et al. 2011). In their study of Philippine geckos, Siler et al. (2010)
were convinced that, though the Pleistocene geography model has
influenced terrestrial biodiversity patterns, it might be an
oversimplified paradigm, and that clade age, phylogenetic
diversification, ease of dispersal, and post-Pleistocene geography may
be invoked to explain vertebrate species diversity.
Philippine plant biogeography
But do the same biogeographic
expectations hold for Philippine plants? Do non-vagile species have
distributions that reflect the predictions of the Pleistocene model,
while more easily-dispersed species show more complex biogeographic
patterns? Surprisingly, this model has never been examined in
Philippine plants. In fact, of the 74 references in ISI Web of Science
that included the search terms “Philippine biogeography”,
only three were on plants (Tan 1996; Linis 2009; Linis 2010). All
three studies concerned mosses, they were based soley on distribution
data for individual Philippine islands, and none of them used
phylogenetic methods to test the model. Biodiversity studies on
Philippine plants are greatly lacking. A complete flora for the
country is lacking with the checklist of Merrill dating to 1923.
Botanical surveys for the Philippines lag behind other comparable
Malesian regions, with Java and Peninsular Malaysia having at least 187
and 145 plant specimen collections per 100 sq km, respectively, while
the Philippinesis a paltry 84 (Tan and Rojo 1989). Only <2% of the
country’s flora have also been evaluated by the International
Union for Conservation of Nature (IUCN; Catibog-Sinha and Heaney 2006).
Even several species of Rafflesia, the world’s largest flower,
known to grow to over 3 feet in diameter, have practically gone
undetected in the Philippines for the past 150 yrs, and it was only in
the last decade that 8 new species have been discovered, thus bringing
the national total to 10 (Barcelona et al. 2009, 2011). Incredibly, all
but one of these species are single-island endemics, and seem to follow
the Pleistocene model. A phylogenetic study of the group is
underway to confirm this.
We hope that through this website, we can motivate phylogenetic and
biogeographic studies on Philippine plants, to learn the mechanistic
processes of evolution in island archipelagoes, to understand how
ancient geology, Pleistocene geography, and tropical climate, acting on
a matrix of many islands of varying sizes, ages and proximities have
come together to produce a unique smorgasbord of species. This
work is urgent given that many of these species, sadly teetering on the
brink of extinction, exist in one of the world’s most severely
threatened biological hotspots.
Barcelona, J. F., P. B Pelser, D. S. Balete, and L. L. Co. 2009.
Taxonomy, ecology, and conservation status of Philippine Rafflesia
(Rafflesiaceae). Blumea 54: 77-93.
Barcelona, J. F., E. S. Fernando D. L. Nickrent, D. S. Balete,
and P. B. Pelser. 2011. An amended description of Rafflesia
leonardi and a revised key to Philippine Rafflesia (Rafflesiaceae).
Phytotaxa 24: 11-18.
Carpenter, K.E. and V.G. Springer. 2005. The center of the center of
marine shore fish biodiversity: the Philippine Islands. Environmental
Biology of Fishes 72: 467–480.
Esselstyn, J.A. and R.M. Brown. 2009. The role of repeated sea-level
fluctuations in the generation of shrew (Soricidae: Crocidura)
diversity in the Philippine Archipelago. Molecular Phylogenetics and
Esselstyn, J.A. et al. 2009. Do geological or climatic processes drive
speciation in dynamic archipelagos? The tempo and mode of
diversification in Southeast Asian shrews. Evolution 63-10:
Evans, B.J. et al. 2003. Phylogenetics of fanged frogs: testing
biogeographical hypotheses at the interface of the asian and Australian
faunal zones. Systematic Biology 52:794–819.
Hall R. 1998. The plate tectonics of Cenozoic SE Asia and the
distribution of land and sea. In: Hall R and Holloway JD, eds.
Biogeography and Geological Evolution of
South East Asia. Leiden: Backhuys Publishers, 99–131.
Hall R. 2002. Cenozoic geological and plate tectonic evolution of SE
Asia and the SW Pacific: computer-based reconstructions and animations.
Journal of Asian Earth Sciences 20: 353–434.
Heaney, L.R. and J.C. Regalado, Jr. 1998. Vanishing Treasures of the Philippine Rainforest. The Field Museum, Chicago.
Heaney, L.R. et al. 2004. Philippines. In R.A. Mittermeier, P.R. Gil,
M. Hoffman, J. Pilgrim, T. Brooks, C.G. Mittermeier, J. Lamoreux, and
G.A.B. da Fonseca (eds.), Hotspots Revisited: Earth’s
Biologically Richest and Most Endangered Terrestrial Ecoregions. Mexico
Heaney, L.R. et al. 2005. The roles of geological history and
colonization abilities in genetic differentiation between mammalian
populations in the Philippine archipelago. Journal of Biogeography 32:
Jansa, S.A. et al. 2006. The pattern and timing of diversification of
Philippine endemic rodents: evidence from mitochondrial and nuclear
gene sequences. Systematic Biology 55:73–88.
Jones, A.W. and R.S. Kennedy. 2008. Evolution in a tropical
archipelago: comparative phylogeography of Philippine fauna and flora
reveals complex patterns of colonization and diversification.
Biological Journal of the Linnean Society 95: 620–639.
Linis, V.C. 2009. Biogeography of Mindoro mosses. Blumea 54: 290–296.
Linis, V.C. 2010. The moss flora of Camiguin Island, Philippines and
their floristic relations to some adjacent islands in the archipelago.
Telopea 12: 525–542.
MacArthur, R.H. and Wilson, E.O. 1967. The Theory of Island Biogeography. Princeton, N.J.: Princeton University Press.
McGuire, J.A. and K.B. Heang. 2001. Phylogenetic systematics of
Southeast Asian flying lizards (Iguania: Agamidae: Draco) as inferred
from mitochondrial DNA sequence data. Biological Journal of the Linnean
Society 72: 203–229.
Myers, N. et al. 2000. Biodiversity hotspots for conservation priorities. Nature 403: 853–858.
Oliveros, C.H. and R.G. Moyle. 2010. Origin and diversification of
Philippine bulbuls. Molecular Phylogenetics and Evolution 54:
Peterson, A.T. et al. 2000. Distribution of the birds of the
Philippines: biogeography and conservation priorities. Bird
Conservation International 10:149–167.
Roberts, T.E. 2006. Multiple levels of allopatric divergence in the
endemic Philippine fruit bat Haplonycteris fischeri (Pteropodidae).
Biological Journal of the Linnean Society 88: 329–349.
Siler, C.D. et al. 2010. Phylogeny and biogeography of Philippine
bent-toed geckos (Gekkonidae: Cyrtodactylus) contradict a prevailing
model of Pleistocene diversification. Molecular Phylogenetics and
Siler, C.D. et al. 2011. Phylogeny of Philippine slender skinks
(Scincidae: Brachymeles) reveals underestimated species diversity,
complex biogeographical relationships, and cryptic patterns of lineage
diversification. Molecular Phylogenetics and Evolution 59:53–65.
Sinha, C.C. and L.R. Heaney. 2006. Philippine biodiversity: Principles and Practice. Manila: Haribon Foundation Inc.
Steppan S.J. et al. 2003. Molecular phylogeny of the endemic Philippine
rodent Apomys (Muridae) and the dynamics of diversification in an
oceanic archipelago. Biological Journal of the Linnean Society 80:
Tan, B.C. 1996. Biogeography of Palawan mosses. Australian Systematic Botany 9: 193–203
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Co's Digital Flora of the Philippines. www.philippineplants.org
Copyright © 2011, Co's Digital
Flora of the Philippines
Last updated October 21, 2012