Biological diversity in Polynesia-Micronesia

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Published: January 22, 2008, 12:00 am
Updated: December 1, 2011, 12:58 pm
Topic Editor: Mark McGinley
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This hotspot includes all the islands of Micronesia and Polynesia, plus Fiji, scattered across 40 million km2 of the Pacific Ocean. Included in this enormous expanse are at least 4,500 islands, representing 11 countries, eight territories, and one U.S. state (Hawaii). The hotspot, which is one of the smallest hotspots in terms of land area, covering only 46,488 km2 (the size of Switzerland), stretches from the Mariana and Palau archipelagos in the northwest to Easter Island (Rapa Nui) in the east, and from the Hawaiian Islands in the north to the Cook Islands, Tonga, and Niue in the south.

Geologically, the islands of Polynesia-Micronesia vary from rocky islets, low-lying coral atolls, and uplifted limestone islands to larger, higher volcanic islands such as those found in Hawaii, Fiji, and Micronesia that support most of the human population in the region. Ongoing or potential volcanic activity is found in Hawaii, Tonga, Samoa, and the Northern Mariana Islands.

A wide range of ecosystems are found throughout this hotspot. There are 12 principal vegetation biomes, the most widespread of which is strand vegetation, consisting of salt-tolerant plants found along the shores of most Pacific Islands. Other principle vegetation associations include mangroves, coastal wetlands, tropical rainforests (Terrestrial biome), cloud forests, savannas (Terrestrial biome), open woodlands, and shrublands.

Unique and Threatened Biodiversity

The wide geographic range and thousands of isolated island ecosystems have led to extremely high levels of endemism in the Polynesia-Micronesia hotspot.

Plants

There are roughly 5,330 species of vascular plants native to Polynesia-Micronesia, of which more than 3,070 (58 percent) are endemic. One family, the Degeneriaceae, is endemic to Fiji, and includes a single tree species, Degeneria vitiensis , which is of considerable scientific interest because of its unique primitive floral characters. In some isolated parts of the hotspot, like Hawai’i, endemism is quite marked; indeed, 87 percent of the vascular plants on Hawai’i are endemic, such that it is sometimes treated as a single floristic region.

Among the noteworthy plants found in the hotspot are the Hawaiian silverswords (Argyroxiphium spp.), a group of five endemic species found only on the slopes of Hawai’i's highest volcanoes. When the plants are about 10-15 years old, they grow two-meter high stalks that briefly display magnificent blossoms before dying.

Unfortunately, many of these plants are highly threatened. Alarmingly, there are currently more invasive than native plant species in Hawai’i. More than half of the remaining native flora on Hawaii have fewer than 5,000 individuals each in wild populations. At least 14 species are down to only a single remaining individual in the wild, and an additional 46 species have only 2-10 individuals remaining in the wild.

Vertebrates

Birds

Collared lory.jpg The collared lory (Phigys solitarius) is found exclusively in the Fijian Islands. Nearly 70 percent of the bird species in this hotspot are found no where else in the world. (Source: © James Stanfield/National Geographic Society)

Birds are the dominant terrestrial vertebrates in the Pacific, and the Polynesia-Micronesia hotspot is home to about 290 regularly occurring species, roughly 160 of which are endemic (an additional 25 species that were endemic became extinct after the arrival of Europeans). In general, avian endemism increases with the isolation and topographic diversity of the islands, with most endemic species being found in the larger and higher islands. The high level of endemism seen at the species level is also manifested at the genus level, with around one-quarter of the genera represented found only in this hotspot. Perhaps not surprisingly then, BirdLife International has identified no less than 15 Endemic Bird Areas confined entirely to the islands in Polynesia-Micronesia.

The Hawai'i honeycreepers, belonging to the finch subfamily Drepanididae, are one of the best-known bird groups in the region. They represent one of the world's most splendid examples of adaptive radiation. Eighteen genera and 34 extant and recently extinct species are believed to have evolved from a single North American finch ancestor. Bill morphology is vastly different among these species, ranging from massive, conical, seed-cracking beaks, to slender, recurved, nectivorous beaks, and even a spectacular wood-pecking variation in the 'Akia pola'au (Hemignathus lucidus). Unfortunately, in addition to eight Critically Endangered species, six more are considered Endangered and four Vulnerable. Thirteen honeycreepers have already gone extinct, and another, the Po'o-uli (Melamprosops phaeosoma ), currently listed as Critically Endangered, was declared by scientists in Hawai'i to be extinct after the last individual died in captivity in November, 2004.

The dispersal of birds to the islands in the middle of the vast Pacific Ocean is just as remarkable. Fruit doves, imperial pigeons, lorikeets, reed warblers, monarch flycatchers, kingfishers, and, strangest of all, rails and ground doves, have repeatedly crossed vast expanses of ocean to colonize islands in Polynesia and Micronesia.

Mammals

The only terrestrial mammals native to Polynesia-Micronesia are 15 species of bats, of which 11 are endemic. Two other endemic bat species have gone extinct. Most bat species are restricted to the high islands (Mariana Islands, Palau, Chuuk (or Truk), Kosrae, Pohnpei, Yap, Samoa, Fiji, and the Hawaiian Islands). The Fijian monkey-faced flying fox (Pteralopex acrodonta , CR), one of the most primitive species of fruit bats in the world, is the only mammal endemic to Fiji.

A single pinniped species, the Hawaiian monk seal (Monachus schauinslandi, EN) is an endemic breeding species in this hotspot and brings the total number of mammals to 16. Breeds mainly on the northwestern Hawaiian islands, they are thought to number fewer than 1,500 individuals.

Reptiles

Banded iguana.jpg The banded iguana (Brachylophus fasciatus, EN) is found throughout Fiji and Tonga and has been introduced to Vanuatu. (Source: © Jean-Paul Ferrero/Ardea London)

There are more than 60 species of native terrestrial reptiles in Polynesia-Micronesia, including seven snakes, the saltwater crocodile (Crocodylus porosus) and more than 50 lizards. Over 30 reptile species are endemic. This reptile fauna is almost entirely Indo-Pacific in origin, with the exception of two species of iguana, the Fiji banded iguana (Brachylophus fasciatus, EN) and Fiji crested iguana (Brachylophus vitiensis , CR), which are endemic to the Fiji-Tonga area and the only species with close relatives from the Americas. The sub-fossil remains of a giant iguana species have been found in Tonga and Fiji.

A fascinating phenomenon among reptiles has been the spread of Lepidodactylus geckos across the region. These geckos are parthenogenic, meaning that they do not need males to reproduce, and can colonize new islands more easily than other geckos that rely on finding other individuals to reproduce sexually.

Besides the 30-odd species endemic to this hotspot, two reptile genera are endemic: the genus Brachylophus (which comprises the two species of iguanas), and the genus Ogmodon, represented by a single species, the venomous 'bola' or Fiji snake (O. vitianus, VU) which, as its name implies, occurs only on Fiji and is a member of the cobra family. A third endemic genus, Tachygia, which included a single skink species formerly restricted to Tonga, is extinct.

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Amphibians

Only three amphibians are native to the hotspot, and all are ranid frogs of the genus Platymantis. Two species are endemic to Fiji, the Fiji tree frog (Platymantis vitiensis) and Fiji ground frog (P. vitiana, EN), and one, the Palau frog (P. pelewensis), is endemic to Palau. All three species are related to other Platymantis species in the Solomon Islands and in New Guinea.

Freshwater Fishes

Although there are no truly freshwater fishes in Polynesia-Micronesia, other than introduced species, nearly 100 native species are found in freshwater as adults (having pelagic marine larval stages); about 20 of these are endemic. Goboid fishes of the families Gobiidae and Eleotridae comprise the largest element of the freshwater fish fauna in the hotspot, and many of these are restricted to a single island or island group. Hawai'i has five species of gobioid fishes (four endemic), while Guam in western Micronesia has four times as many.

Invertebrates

Invertebrate diversity in Polynesia-Micronesia is high for certain groups, particularly land snails, which are a conspicuous feature of Pacific Island ecosystems. Of the 13 major indigenous pulmonate land snail families on the Pacific Islands, four are endemic to the central Pacific. The Hawaiian Islands have more than 763 species, of which a staggering 748 are endemic. The Samoan Islands have 99 native species, of which 64 are endemics. The land snails of the subfamily Achatinellinae are among the most remarkable: in some parts of Hawai’i, these brilliantly colored snails may number as many as 2,000 individual snails per tree.

Human Impacts

Iiwi.jpg The I'iwi (Vestiaria coccinea) is a member of the honeycreeper family (Drepanididae), endemic to Hawaii. This family has suffered numerous extinctions in recent times. (Source: © Peter LaTourette/Vireo)

As a result of their isolation and small size, the island ecosystems of the Polynesia-Micronesia hotspot are exceedingly vulnerable to habitat degradation and the introduction of [[invasive] species]. Due mainly to these threats, species in this hotspot are some of the most endangered in the world. Species extinction rates are among the highest in the world, especially for birds and reptiles.

Human activities have threatened the unique biodiversity in Polynesia-Micronesia for at least 3,000 years, since the first Polynesian people began to migrate east from Southeast Asia and New Guinea. Micronesians are linguistically different from the Polynesians and show a clear migration from the Philippines, both prehistorically and contemporarily. These earliest settlers introduced several plants and animals, which they used for food, medicine, building materials, and ornamentation. They converted land for agriculture and hunted many birds and reptiles to extinction. The fossil record for the Pacific Islands reveals that as many as 2,000 bird species may have disappeared since humans colonized the islands.

Over the years, human-induced disturbance has resulted in the establishment of savannas, grasslands, and secondary forests throughout the region. Small islands, in particular, are heavily impacted by conversion of natural vegetation to anthropogenic landscapes. In many Pacific islands, there is no natural lowland vegetation left, because the land is under such demand from human populations, which are growing by one to three percent a year. In Fiji, for example, logging has affected nearly all the lowland forests. Overall, the combined effects of agriculture, logging and development have left only 10,015 km2, or 21 percent of the region's original vegetation, in more or less pristine condition throughout the Polynesia-Micronesia hotspot. Increasing urbanization and commercialization has also led to the loss of traditional knowledge and resource management techniques in many areas, leading to further environmental degradation.

Isolation has left the island biota extremely vulnerable to invasive alien species, especially introduced predators and browsers. The native biota of the islands evolved for millions of years in the absence of mammalian predators, and the introduction of rats, pigs, goats, feral cats, and mongooses has had a devastating effect on small vertebrate populations on many islands. In some areas, birds also are threatened with extinction from avian malaria that was introduced with alien mosquito species. Some non-native species of ants and snails have also been highly destructive when introduced.

Two classic case studies serve to highlight the severity of the threat of invasive alien species on the endemic native fauna of the Pacific. The first example concerns the impact of the brown tree snake (Boiga irregularis) in Guam. The snake was inadvertently introduced in the early 1950s to the island by military ships and has already caused the extinction of nine native bird species and all endemic lizard species on the island. This mainly arboreal and nocturnal tree snake, which has reached densities of 4,600 per km2 on Guam, has now been found on neighboring islands (it has even been found on cargo ships docked in Hawai'i on several occasions) as well and may be established on Saipan. The second classic example concerns the introduction of the predatory snail Euglandina rosea from the southeastern United States to the Society Islands for purposes of biological control. This species single-handedly resulted in the loss of 57 of the {C}archipelago's 61 endemic partulid land snails.

The impacts of non-native plants can be just as damaging, as invasive species out-compete and replace native ones. Habitat fragmentation and degradation increases the destructiveness of invasive plant and animal species, many of which favor secondary forest and edge areas. Sadly, in present-day Hawaii there are more non-native plant species than native ones. One fast-growing South American tree species, Miconia calvescens, has crowded out much of the native vegetation in Tahiti, and is now estimated to cover 65 percent of the island.

Other pressures on biodiversity include the hunting and trapping of bats, birds, and other species. Species at risk include the coconut crab (Birgus latro) and pigeons (especially Ducula and Ptilinopus). The overharvesting of birds and bats can be particularly harmful, since these species often act as pollinators and seed dispersers for native plant species. Another threat is fire, which is often used to clear land. Sea level rise due to global warming is a major concern, as low-lying atolls, including Tokelau, Tuvalu, Kiribati, and the Marshall Islands, are at risk of disappearing completely under rising waters. Natural phenomena such as cyclones and floods can also extirpate isolated populations.

Conservation Action and Protected Areas

Mount otemanu.jpg Mount Otemanu on Bora-Bora island in French Polynesia. (Source: © Art Wolfe)

At least 356 protected areas exist in the Polynesia-Micronesia hotspot, covering 18,722 km2 of land and sea. Almost one-third of these are found in Hawaii. Excluding Hawaii, about 154, or 60 percent, of these protected areas are terrestrial, accounting for about 6.7 percent of the land area of the hotspot. However, figures relating to coverage must be taken as approximates for two reasons. The first is that many protected areas have no recorded size, partly because boundaries have not been defined or updated. Also, communities are sometimes hesitant about publicizing information about locally managed areas. There are many temporary and permanent closures that constitute protected areas, but which are not recognized by national governments. An analysis using the World Database on Protected Areas gives a lower number of protected areas in the hotspot.

Even after taking into account traditionally managed areas, many more protected areas are needed to conserve the varied and unique biodiversity of this region. One way of ensuring that the network of protected areas adequately conserves biodiversity is through the identification and conservation of Key Biodiversity Areas (KBAs), globally important sites for biodiversity conservation. For Polynesia-Micronesia, KBAs this process was led by CI's Melanesia program in partnership with the Secretariat for the Pacific Regional Environment Programme (SPREP), WCS-Pacific Islands, TNC-Micronesia, the Societe d'Ornithologie de la Polynasie, the Delegation a la Recherche de la Polynasie francaise, Te Ora Fenua (Tahiti Conservation Society) and the Bishop Museum. Of the 162 sites, only roughly one-third are within existing or planned protected areas.

Most current conservation investment in the region occurs in the form of relatively small grants. Multilateral donors include the Asian Development Bank (ADB) and United Nations agencies, mainly through GEF enabling activities and mid-size projects. Bilateral donors include mainly the governments of New Zealand, Australia, Japan, France and the United States. Except in the most developed nations, a lack of capacity and technical infrastructure impedes the ability of governments to implement conservation projects. Nevertheless, it is important to highlight successes such as the Takitumu Conservation Area in the Cook Islands.

During the past several thousand years, the Pacific has arguably lost more species to extinction than any other region on Earth. Thus, coordinated regional efforts above and beyond the establishment of protected areas are needed to share information and address common threats, such as invasive alien species, are showing great promise and offer the best hope for preserving what remains of the extraordinary biota of the Polynesia-Micronesia Hotspot. One example is the technique of translocating threatened species to nearby islands and eradicating [[invasive] species]. For example, the Rarotongan monarch or Kakerori (Pomarea dimidiata, EN) was downlisted from Critically Endangered to Endangered status in the Cook Islands, following 15 years of intensive management involving predator control and translocation to the nearby rat-free island of Atiu. An important Pacific-wide effort was funded in 2004 by the New Zealand Government: the Pacific Islands Cooperative Initiative on Invasive Species, which aims to control and eradicate alien invasive species. The main partners in this initiative are the IUCN Invasive Species Specialist Group, Cl, SPREP and SPC.

Because so much of the biota of Polynesia-Micronesia remains unknown, there is a crucial need for a comprehensive biological survey to guide conservation in the region. Plants, land snails, and flying foxes are particularly understudied. The Pacific Science Association, the Bishop Museum, SPREP, the U.S. Geological Survey (USGS), and others are working on major initiatives such as the Pacific Biological Survey and the Pacific Basin Information Facility. More localized biodiversity surveys are also underway, initiative by Fiji, French Polynesia and other nations.

Using a $10 million grant from the Global Environment Facility (GEF), through UNDP, SPREP executed the South Pacific Biodiversity Conservation Programme (SPBCP) to establish and manage a series of large, diverse Conservation Areas throughout the region between 1993 and 2001. The Roundtable for Nature Conservation, facilitated by SPREP, is working with national governments to determine regional priorities and develop and implement the resulting action plans for combating invasive species and conservation whales and dolphins, marine turtles, dugongs and avifauna.

Further Reading

  • Allison, A. 1996. Zoogeography of amphibians and reptiles of New Guinea and the Pacific region. In A. Keast & S.E. Miller. (Eds.), Origin and Evolution of Pacific Island Biotas, New Guinea to Eastern Polynesia: Patterns and Processes. Amsterdam: SPB Academic Publishing.
  • Allison, A. 2003. Biological surveys: New perspectives in the Pacific. Organisms Diversity and Evolution 3:103-110.
  • Allison, A. & Miller, S.E. 2000. Hawaii biological survey: Museum resources in support of conservation. In P.H. Raven & T. Williams. (Eds.), The Quest for a Sustainable World. pp. 281-290. Washington, D.C.: National Academy Press. ISBN: 0309065550.
  • Balgooy, M.M.J. van. 1993. Pacific Plant Areas, Vol. 5. Leiden, The Netherlands: Rijksherbarium.
  • Coote, T. & Loeve, E. 2003. From 61 species to five: Endemic tree snails of the Society Islands fall prey to an ill-judged biological control programme. Oryx 37:91-96.
  • Cowie, R.H. 1996. Pacific island land snails: Relationships, origins, and determinants of diversity. In A. Keast & S.E. Miller. (Eds.), Origin and Evolution of Pacific Island Biotas, New Guinea to Eastern Polynesia: Patterns and Processes. pp. 347-372. Amsterdam: SPB Academic Publishing.
  • Cowie, R.H. 1998. Catalog of the non-marine snails and slugs of the Samoan Islands. Bishop Museum Bulletin in Zoology 3:1-122.
  • Cowie, R.H. & Robinson, A.C. 2003. The decline of native Pacific island faunas: Changes in status of the land snails of Samoa through the 20th century. Biological Conservation 110:55-65.
  • Cowie, R.H., Evenhuis, N.L. & Christensen, C.C. 1995. Catalog of the Native Land and Freshwater Mollusks of the Hawaiian Islands. Leiden: Backhuys Publishers.
  • Crombie, R.I. & Steadman, D.W. 1986. The lizards of Rarotonga and Mangaia, Cook Islands group, Oceania. Pacific Science 40(1-4): 44-57.
  • Eldredge, L.G. 2000. Non-indigenous freshwater fishes, amphibians, and crustaceans of the Pacific and Hawaiian Islands. In Invasive Species in the Pacific: A Technical Review and Draft Regional Strategy. Apia: South Pacific Environment Programme. ISBN: 982040214X.
  • Eldredge, L.G. & Evenhuis, N.L. 2003. Hawaii's biodiversity: A detailed assessment of the numbers of species in the Hawaiian Islands. Bishop Museum Occasional Papers 76:1-28.
  • Fitzsimmons, J.M., Parham, J.E. & Nishimoto, R.T. 2002. Similarities in behavioral ecology among amphidromous and catadromous fishes on the Oceanic islands of Hawaii and Guam. Environmental Biology of Fishes 654:123-129.
  • Flannery, T.F. 1995. Mammals of the South-West Pacific and Moluccan Islands. Sydney: Reed. ISBN: 0801431506.
  • Gibbons, J.R.H. 1981. The biogeography of brachylophus (iguanidae) including the description of a new species, B. vitiensis, from Fiji. Journal of Herpetology 15(3):255-273.
  • Hadfield, M.G. 1986. Extinction in Hawaiian achantinelline snails. Malacologia 27:67-81.
  • Holland, B. S. & Hadfield, M.G. 2002. Islands within an island: Phylogeography and conservation genetics of the endangered Hawaiian tree snail, Achatinella mustelina. Molecular Ecology 11:365-375.
  • Ineich, I. & Zug, G. 1996. Tachygia, the giant tonga skink: Extinct or extant. Cryptozoology 12:30-35.
  • James, H. F. & Olson, S. L. 1991. Descriptions of Thirty-two New Species of Birds from the Hawaiian Islands: Part II. Passeriformes, volume No. 46 of Ornithological Monographs. Washington, D.C.: The American Ornithologist's Union.
  • Lydeard, C., Cowie, R.H., Ponder, W.F., Clark, S., Bogan, A.E.,Bouchet, P., Cummings, K.S., Frest, T.J., Herbert, D.G., Hershler, R., Gargominy, O., Perez, K., Roth, B., Seddon, M., Strong, E.E. & Thomopson, F.G. In press. The global decline of nonmarine mollusks. BioScience April 2004.
  • McDowall, R.M. 2003. Hawaiian biogeography and the islands: Freshwater fish fauna. Journal of Biogeography 30:703-719.
  • Meyer, J.Y. & Florence, J. 1997. Tahiti's native flora endangered by the invasion of Miconia calvescens DC (Melastomataceae). Journal of Biogeography 23:775-781.
  • Mueller-Dombois, D. & Fosberg, F.R. 1998. Vegetation of tropical Pacific islands. New York: Springer-Verlag. ISBN: 038798285X.
  • Olson, S.L. & James, H.F. 1991. Descriptions of thirty-two new species of birds from the Hawaiian Islands: Part I. Non-passeriformes, Vol. 45 of Ornithological Monographs. Washington, D.C.: The American Ornithologist's Union.
  • Pratt, H.D., Bruner, P.L. & Berrett, D.G. 1987. The Birds of Hawaii and the Tropical Pacific. Princeton: Princeton University Press. ISBN: 0691084025.
  • Reti, I. 1993. The South Pacific Biodiversity Conservation Programme: Its concept and scope. Pacific Science Association Information Bulletin 45(1-2):9-14.
  • Ryan, P. A. 1991. The success of the gobiidae in tropical insular streams. New Zealand Journal of Zoology 18:25-30.
  • SPC (Secretariat of the Pacific Community)
  • SPREP (South Pacific Regional Environmental Programme). 2003. Action Strategy for Nature Conservation in the Pacific Islands Region, 2003-2007. Apia, Samoa: South Pacific Regional Environment Programme.
  • Stoddart, D.R. 1992. Biogeography of the tropical Pacific. Pacific Science 46(2): 276-293.
  • Takhtajan, A.L. & Cronquist, A. 1986. Floristic Regions of the World. Berkeley: University of California Press. ISBN: 0520040279.
  • Tomich, P.Q. 1986. Mammals of Hawaii. Honolulu: Bishop Museum Press. ISBN: 0930897102.

Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Conservation International. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the Conservation International should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.


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