The Philippines is a center of endemism, with many species occuring on specific islands only. The reason for this extremely high rate of endemicity is its history during the ice ages. As can be seen in figure 1, even during the last ice-age (approximately 12.000-15.000 years ago) the Philippines were already an archipelago and not connected to mainland Asia as so many other islands. When climate changes and global temperatures drop, the north and south poles expecially, become much colder and sea water freezes there to create glaciers and ice caps. The storage of all this water in the form of ice, causes global ocean water levels to drop up to more than 100 meters! The result is that some islands, which were previously separated from each other or the mainland, all of a sudden become connected, allowing easier movement of species across land, and thus exchange of genetic material between previously separated populations. Especially in South-east Asia this is very visible, as can be seen in figure 1. However while other islands in South-east Asia were at that time connected to the mainland (like Borneo, Java and Sumatra), the Philippines was separated by deep water channels. The result is that many of the species living in the Philippines have been separate populations for a very long time, allowing them to develop into separate species and subspecies, while other islands in the region share a lot of animal and plant species with the mainland and each other.
However, also within archipelagos, such as the Philippines, these land bridges developed up to a point. As can be seen in Figure 2, the Philippines looked different then. Many of the 7107 islands that exist today were then linked together into bigger islands. These islands are called the ‘Greater Islands’ or ‘Ice-age Islands’ and represent the major Philippine faunal regions. Species could at that time freely distribute along those larger areas which later became separate islands. There are six major faunal regions in the Philippines. These are:
- Greater Luzon (Luzon Island with Catanduanes, the Pollilos and other small satelite islands)
- Mindoro (which is surrounded by deep water and has only very few small islands around it that were connected to it then, such as Ilin Island)
- West Visayas (Negros, Panay, Cebu, Guimaras, Masbate & Ticao)
- Greater Mindanao (Mindanao mainland including Samar, Leyte, Bohol and smaller islands such as Basilan, Dinagat and Surigao)
- Sulu Archipelago (Tawi-Tawi, Jolo etc.)
- Greater Palawan (Palawan, Calamianes Islands, Balabac)
Besides these faunal regions, there are some smaller islands/Island groups, that were not connected to other islands at that time, such as the Batanes and Babuyan Islands, Romblon and Tablas, Siquijor & Camiguin Sur. These smaller islands also developed their own set of animals, many of which are unique to each island.