Polynesia-Micronesia

Allen Allison⁸⁷ and Lucius g. Eldredge⁸⁷

The Polynesia-Micronesia Hotspot consists of all of Micronesia and tropical Polynesia, and also Fiji, which is generally considered a transitional area between Melanesia and Polynesia. Furthermore, we include the Hawaiian Islands within this hotspot, although its flora is so distinct, with 87% of 1 170 total native vascular plant species endemic (updated from Eldredge and Evenhuis, 2003), that it is usually treated as a separate floristic kingdom (Takhtadzhëiìan and Cronquist 1986). Although it stretches over an enormous area of some 21.6 million km² of Pacific Ocean (2.6 times the size of the continental United States), it is in fact one of the smallest hotspots in terms of land area (roughly 47 000 km² in size).

Stretching from the Mariana and Palau archipelagos in the west to Easter Island (Rapa Nui) in the east, and from the Hawaiian Islands in the north to the Cook Isands, Tonga, and Niue in the south, the Polynesia-Micronesia Hotspot includes at least 1 415 islands belonging to 11 countries, eight territories, and one American state. In Polynesia, the independent nations are the Cook Islands (237 km²), Niue (259 km²), Samoa (2 935 km²), Tonga (649 km²), and Tuvalu (26 km²), and Fiji (18 333 km²) and, in Micronesia, the Federated States of Micronesia (701 km²), Kiribati (811 km²), the Marshall Islands (181 km²), Nauru (21 km²), and Palau (488 km²). The territories in Polynesia include the French territories of Wallis and Futuna (274 km²) and French Polynesia (3 521 km²), the American territory of American Samoa (200 km²), the British territory of Pitcairn Islands (47 km²), the New Zealand territory of Tokelau (10 km²), and the Chilean territory of Easter Island (166 km²). In Micronesia, the American territories are Guam (541 km²) and the Northern Mariana Islands (477 km²). Finally, the one American state in the region is Hawaii (16 642 km²) (SPC 2003).

The islands in the region differ widely in geological composition, ranging from ancient highly weathered rocky islets, low-lying coral atolls, and uplifted limestone islands (makatea) to much larger, high volcanic islands such as those found in Hawaii, Fiji, and Micronesia that support most of the human population in the region (Stoddart 1992). Ongoing volcanic activity is found in Hawaii, Tonga, Samoa, and the Northern Mariana Islands.

This region is biologically very diverse, with Pacific Island plants occurring in 12 principal vegetation associations or biomes (Mueller-Dombois and Fosberg 1998). The most widespread association is strand vegetation, consisting of salt-tolerant plants found along the shores of most Pacific Islands. Inland areas with high rainfall support various types of mesic forest or rainforest, generally typified by high stature trees at low elevations, and lower stature trees and a higher percentage of shrubs and epiphytes at higher elevations. Areas at the cloud line are dominated by cloud forest, while areas above the cloud line – which in this region are limited to mountain summits on Maui and the island of Hawaii – are covered in an open woodland association of grassland and xerophytic shrubs. In addition, there are some 515 wetlands scattered throughout the region, with 386 in the Hawaiian Islands alone and 129 in the remainder of the region. Included among the wetlands are some 500 km² of mangrove forests, composed of 22 species, declining in diversity from west to east across the Pacific, reaching a limit in American Samoa, where only a single mangrove species is present.

In general, there is a high degree of endemism among both vascular plants and certain animal groups. The actual number of native vascular plants (ferns and flowering plants) in the hotspot is unknown. Davis et al. (1997) listed 3 074 species of endemic vascular plants. The overall rate of vascular plant endemism in the hotspot is about 58%; based on this, we estimate that the hotspot flora includes about 5 330 native species of vascular plants; these are represented by 159 families and 802 genera, of which 63 genera are endemic to the hotspot (Van Balgooy 1993). One of the families, the Degeneriaceae, is endemic to the hotspot and is represented by a single species, Degeneria vitiensis, which is endemic to Fiji.

In terms of animal diversity, the terrestrial animal associations of Polynesia-Micronesia include rich arrays of birds, reptiles, land snails, and insects, all groups adept at crossing gaps of open sea. Birds are the dominant terrestrial vertebrates in the Pacific, and many groups have radiated extensively throughout the region. There are around 300 regularly occurring species in the region, of which 242 regularly breed within the hotspot and 170 are endemic (an additional 25 species that were endemic went extinct since the arrival of Europeans) (updated from Pratt et al. 1987). In general, the number of endemic species increases with the geographic isolation and topographic diversity of the different archipelagos, with most of the endemic species being forest birds found in the larger and higher islands. Generic endemism is also high, with 28 of 111 genera endemic. Not surprisingly then, no less than 15 Endemic Bird Areas have been identified within the Polynesia-Micronesia Hotspot (Stattersfield et al. 1998). One of the best-known bird groups, and one of world's most spectacular cases of adaptive radiation and speciation in an isolated island ecosystem, involves the endemic honeycreepers (Drepanididae). Believed to have originated from a single ancestor from North America, the family has evolved into 34 extant and recently extinct species (in 18 genera), although numerous fossil taxa have also been described (Olson and James 1991; James and Olson 1991).

Among reptiles, there are 61 terrestrial species found in Polynesia-Micronesia, including seven species of terrestrial snakes, the saltwater crocodile (Crocodylus porosus), and 53 species of lizards, mostly skinks and geckos, but also including two iguanas, the Fiji banded iguana (Brachylophus fasciatus, EN) and Fiji crested iguana (B. vitiensis, CR), which are endemic to the Fiji-Tonga area. In addition, there are two land-breeding species of marine snakes (Laticauda spp.) and six species of marine turtles found within the hotspot (updated from Allison 1996). Thirty-one reptile species are endemic. This herpetofauna is almost entirely Indo-Pacific in origin, except for the iguanas, whose closest living ancestors are in the Americas (Gibbons 1981). Two reptile genera are endemic to the hotspot: the genus Brachylophus (two species; see above), and the genus Ogmodon, represented by a single species, the Fiji snake (O. vitianus, VU) which, as its name implies, occurs only on Fiji. A third endemic genus, Tachygia, which included a single skink species formerly restricted to Tonga, is extinct. It is likely that there are no native terrestrial species found east of the Cook Islands (Crombie and Steadman 1986).

Other vertebrate groups are characterized by low diversity but high endemism. The native terrestrial mammal fauna, for example, consists entirely of bats. Fifteen living native species of bats are known from this hotspot (including Myotis insularum, which may not represent a valid record for the area), and 11 are endemic, most restricted to the high islands (Mariana Islands, Palau, Chuuk (= Truk), Kosrae, Pohnpei, Yap, Samoa, Fiji, and the Hawaiian Islands) (Tomich 1986; Flannery 1995). An endemic bat, the Fijian monkey-faced bat (Pteralopex acrodonta, CR), is one of the most primitive species of fruit bat known and is the only mammal endemic to Fiji. Similarly, amphibian diversity in this hotspot is also low; only three native amphibians are known to occur, all of them ranid frogs of the genus Platymantis: the Palau frog (P. pelewensis), endemic to Palau; and the Fiji ground frog (P. vitiana, EN) and Fiji tree frog (P. vitiensis), both endemic to Fiji (Allison 1996).

There are no truly freshwater fishes in Polynesia and Micronesia other than some 86 introduced species, such as tilapia, mosquitofish, and others (Eldredge 2000), but at least 96 native species are found as adults in freshwater; 20 species are endemic. Gobioid fishes (Gobiidae and Eleotridae) comprise the largest element of the freshwater fish fauna, especially members of the genera Lentipes, Sicyopterus, Sicyopus, Stiphodon, and Stenogobius. Information on their life history is limited, but it appears that they all have a pelagic marine larval stage. Most have a very limited geographic range, and there are many island or island-group endemics. Hawaii, representing the northernmost island group in Polynesia, has five species of gobioid fishes, whereas Guam in western Micronesia has four times that of Hawaii (Fitzsimmons et al. 2002). Four of the five species in Hawaii are considered endemic (McDowall 2003).

Invertebrate diversity in the region is high for certain groups. Particularly impressive are the land snails, 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 (Cowie 1996). The Hawaiian Islands have a total of 763 native species, of which a staggering 748 are endemic (Cowie et al. 1995); the Samoan Islands have 99 native species, of which 64 are endemic (Cowie and Robinson 2003). The land snails of the subfamily Achatinellinae are considered by many to be the most remarkable of all land snail faunas. Another example of a spectacular adaptive radiation, these brilliantly colored little jewels of the Hawaiian forests reach perhaps as many as 2 000 individuals per tree in some areas (Hadfield 1986).

Unfortunately, the biota of the Polynesia-Micronesia Hotspot is under intense pressure from human-inuced disturbance and habitat loss, alien species introductions, and other factors, and its plants and animals are among the most highly threatened in the world. For example, in Hawaii, approximately 189 plant taxa exist in the wild as multiple populations with fewer than 50 individuals. At least 14 species of Hawaiian endemic plants are down to only one individual in the wild; an additional 46 are down to two to 10 individuals in the wild; and more than half of the native flora of 1 170 species (which is now exceeded in number by alien species) has fewer than 5 000 individuals each in wild populations (updated from Allison and Miller 2000).

Alien species, an especially insidious problem, have contributed to many of the extinctions in the region, including 50% of the achatinelline land snail species (or 50 out of a total of 99 species). Due to alien species and other threats, only 8-10 of these snail species are now considered extant (Holland and Hadfield 2002) and perhaps as many as 90% of the total Hawaiian land snails are extinct (Lydeard et al., in press). Alien plants are also a significant cause of degradation of Pacific ecosystems. Miconia calvescens, for example, is a small, fastgrowing South American tree that has taken over on Tahiti, where it has crowded out native species and covers at least 700 km², or about 65% of the island (Meyer and Florence 1997), while other aggressive plants, such as gorse (Ulex europaeus), banana poka (Passiflora mollissima), and other species, are estimated to have damaged at least 57% of the original forest of the Hawaiian Islands. In the Society Islands, the introduction of a predatory snail for biological control resulted in the loss of 57 of that archipelago's 61 endemic partulid land snails (Coote and Loève 2003).

As a result of all of these factors, and also the impact of guano mining and other land disturbances, more than three-quarters of the original vegetation of Polynesia-Micronesia has been destroyed or substantially modified, with an estimated 10 000 km² or 21% of the original vegetation remaining in more or less pristine condition for the entire hotspot.

The Polynesia-Micronesia Hotspot has a total of 259 terrestrial protected areas and community-based conservation areas that cover a little more than 5 000 km², or just under 11% of all land within the region (SPREP 2003). However, Hawaii has 105 (41%) of these protected areas, or a little more than 58% of the overall area for the region as a whole. The actual level of protection that the various parks and reserves receive varies widely within the region, from those that exist only on paper to the intensely managed national parks of Hawaii. Protected areas coverage is lower according to the World Database on Protected Areas (5.2%).

In terms of strategies, conservation activities will be most effective if undertaken on a regional basis through cooperation among nations, as many of the Pacific Island nations are simply too small and have too few resources to undertake this work individually. Furthermore, many of the problems are regional in nature. The twenty nations, territories, and states in Polynesia-Mironesia have a long history of cooperation in trade and development through the Secretariat of the Pacific Community (SPC) which, in 1978, established the South Pacific Regional Environment Programme (SPREP) to deal specifically with environmental issues. Equipped with a five-year, $10-million grant from the Global Environment Facility (GEF), SPREP was able to form the South Pacific Biodiversity Conservation Programme (SPBCP), and has used this funding to “establish and initially manage a series of large, diverse Conservation Areas (CAs) in which human activities will be guided to protect ecological function” (Reti 1993).

Much of the biota of the Polynesia-Micronesia Hotspot remains unknown, and there is an urgent need for a comprehensive biological survey to guide and inform the development of conservation priorities. Even in Hawaii, which is the best-known archipelago in the hotspot, more than a third of the biota – at least 7 000 species – have not yet been scientifically named (Allison 2003). Bishop Museum and a host of partners, especially the U.S. Geological Survey (USGS), are addressing this issue in Hawaii through the Hawaii Biological Survey, and are working with the Pacific Science Association and governments and NGOs throughout the region to develop a Pacific Biological Survey. The Pacific Science Association is also working with the USGS, the Global Biodiversity Information Facility (GBIF), SPREP, and others to develop a Pacific Basin Information Facility (PBIF) to facilitate Web access to a wide array of currently inaccessible biodiversity information.

During the past several thousand years, the Pacific has arguably lost more species to extinction than any other region on Earth (Steadman 1995). Coordinated regional efforts that are to being developed 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.

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