There are both great similarities and considerable diversity in the ecosystems that evolved on the islands of Oceania in and around the Pacific Ocean. The islands, such as New Zealand, that were originally parts of continents still carry some small plant and animal remnants of their earlier biota (animal and plant life), and they also have been extensively modified by evolution, adaptation, and the arrival of new species. By contrast, the other islands, which emerged via geological processes such as volcanism, possessed no terrestrial life, but over long periods, winds, ocean currents, and the feet, feathers, and digestive tracts of birds brought the seeds of plants and a few species of animals. Only those species with ways of spreading to these islands were able to undertake the long journeys, and the various factors at play resulted in diverse combinations of new colonists on the islands. One estimate is that the distribution of plants was 75 percent by birds, 23 percent by floating, and only 2 percent by wind.

The migration of Oceanic biota was generally from west to east, with four major factors influencing their distribution and establishment. The first was the size and fertility of the islands on which they landed, with larger islands able to provide hospitality for a wider range of species. Second, the further east the islands, generally the less the species diversity, largely because of the distance that had to be crossed and because the eastern islands tended to be smaller, more scattered, and remote. This easterly decline in species diversity is well demonstrated by birds and coral fish. It is estimated that there were over 550 species of birds in New Guinea, 127 in the Solomon Islands, 54 in Fiji, and 17 in the Society Islands. From the west across the Pacific, the Bismarck Archipelago and the Solomon Islands have more than 90 families of shore fish (with many species within the families), Fiji has 50 families, and the Society Islands have 30. Third, the latitude of the islands also influenced the biotic mix, as those islands in relatively cooler latitudes, notably New Zealand, were unsuited to supporting some of the tropical plants with which Pacific islands are generally associated.

Finally, a fourth major factor in species distribution, and indeed in the shaping of Pacific ecosystems, was wind. It takes little experience on Pacific islands to be aware that there are prevailing winds. To the north of the equator these are called north-easterlies, while to the south they are called south-easterlies. Further south, from about 30° south, the winds are generally from the west. As a result on nearly every island of significant size there is an ecological difference between its windward and leeward (away from the wind) sides. Apart from the wind action itself on plants and soils, wind has a major effect on rain distribution. The Big Island of Hawaii offers a prime example: one can leave Kona on the leeward side in brilliant sunshine and drive across to the windward side where the city of Hilo is blanketed in mist and rain.

While such localized plant life and climatic conditions are very noticeable, over Oceania as a whole there is relatively little biodiversity, and the smaller the island and the further east it lies, the less there is likely to be. When humans moved beyond the islands of Near Oceania (Australia, New Guinea, and the Solomon Islands), they encountered no indigenous mammals except for flying foxes, fruit bats, and seals on some islands. Other vertebrate species were restricted to flying animals and a few small reptiles. However, local adaptations and evolution over long periods of isolation promoted fascinating species adaptations to local conditions. Perhaps most notable, in the absence of mammals and other predators, are the many species of flightless and ground-nesting birds. Another consequence of evolution was that many small environments boasted their own endemic (native) species, often small in number, unused to serious predation, limited in range, and therefore vulnerable to disruption. In Hawaii, for example, the highly adapted 39 species and subspecies of honeycreepers, several hundred species of fruit flies, and more than 750 species of tree snails are often cited to epitomize the extent of localized Oceanic endemism (species being native to the area).

在太平洋及其周围的大洋洲岛上所演变出来的生态系统，具有很大的相似性和相当的多样性。新西兰等岛屿原本属于大陆的一部分，但大陆仍然保留了这些岛屿早期生物区系（动植物生命）的一些小型动植物，而且这些动植物也因演化，适应，以及新物种的到来而进行了很大的转变。相比之下，其他岛屿，通过如火山活动一类的地质过程而出现，虽然没有陆地生活，但长期以来，风，洋流，鸟类的脚，羽毛和消化道带来了植物的种子，以及一些动物。只有那些有传播到这些岛屿的物种才能进行漫长的旅程，而各种因素造成岛屿上新定居物种的不同组合。有人估计，植物的分布有百分之七十五是依靠鸟类的传播，百分之二十三是依靠漂流，只有百分之二是依靠风的传播。 海洋生物群的迁移一般是从西向东，其中有四个因素影响其分布和建立。第一是它们所迁移岛屿的大小和土壤肥力，并且较大的岛屿满足更多物种的需要。第二，岛屿越往东，物种多样性就越小，这主要是因为动物它们所必须跨越的距离，因为东部岛屿往往更小，更分散，更偏远。鸟类和珊瑚鱼较好地证明了这种物种多样性的下降。据估计，新几内亚有550多种鸟类，所罗门群岛有127种，斐济有54种，社会群岛有17种。从西面横跨太平洋，俾斯麦群岛和所罗门群岛有90多个海岸鱼类家族（家族内有许多物种），斐济有50个家族，社会群岛有30个。第三，这些岛屿的纬度也影响了生物的组合，因为在相对较冷的纬度地区，特别是新西兰，这些岛屿通常不适合太平洋岛屿上有关的一些热带植物生长。 最后，风是物种分布，以及太平洋生态系统形成的第四个主要因素。人们在太平洋岛屿上对于是否有盛行风，并没有多少经验。赤道以北称为北-东风带，而以南则称为南-东风带。再往南，向南方约30°的地方，风一般都来自西部。因此，几乎每个大小相当的岛屿都有着迎风面和背风面（远离风）的生态差异。除了风力作用本身对植物和土壤的影响外，风对雨水分布也有重要影响。夏威夷岛为我们提供了一个很好的例子：在阳光灿烂的阳光下，你可以在背风的一侧离开科纳，人们可以在灿烂的阳光下将科纳留在下风侧，并驱车穿过雾雨笼罩的希洛市风口处。 虽然这种当地的植物生命和气候条件非常明显，但整个大洋洲的生物多样性相对还是较少，而岛屿越小，离东部越远，就越不可能有生物多样性。当人类离开大洋洲附近（澳大利亚，新几内亚和所罗门群岛）时，除了在一些岛屿上的狐蝠，果蝠和海豹之外，他们没有遇到任何本土的哺乳动物。其他脊椎动物物种也仅限于飞行动物和一些小的爬行动物。然而，在长期的隔绝环境下，物种的局部适应和进化促使它们适应了当地环境。也许最值得注意的是，在没有哺乳动物和其他食肉动物的情况下，存在着许多种不能飞行和在地面筑巢的鸟类。而进化的另一个后果就是，许多小环境会都有自己的地方性（本地）物种，通常数量少，没有被严重掠夺，范围有限，因此易受干扰。例如，在夏威夷，适应度较强的39种蜂类和蜜旋木雀亚种，数百种果蝇和超过750种树蜗牛都被认为是当地特有的海洋物种典型（物种来源于该地区） 。