Philippine Mammals - Distributional Patterns

In describing the distributions of species, we often refer to the zoogeographic regions of the country; these are shown in the figure below (from Heaney, 1986). The map is based on the extent of islands in the Philippines during the late Pleistocene period, about 20,000 years ago, when the development of immense continental glaciers had, in effect, removed water from the world's oceans, so that sea level was 120m lower than it is today (Heaney, 1991a). Each of these Pleistocene islands defines the limit of a distinct fauna (Alcala, 1976; Dickerson, 1928; Everett, 1889; Heaney, 1985b, 1986, 2004). The three largest faunal regions thus defined are the Luzon Faunal Region (including Luzon, Catanduanes, Marinduque, Polillo, and several small islands), the Mindanao Faunal Region (including Mindanao, Basilan, Bohol, Leyte, Samar, and adjacent small islands), and the Palawan Faunal Region (including Palawan, Balabac, Busuanga, Culion, Cuyo, and adjacent small islands). Other islands coalesced into Pleistocene islands larger than those of today (e.g., there was a single island fromTawi-tawi to Jolo, and an island including Negros, Panay, Cebu, and Masbate), whereas other islands remained isolated (e.g., Camiguin, Sibuyan, Siquijor, and Mindoro).

The recognition of these faunal regions is an important aid in understanding the present distribution of Philippine mammals. However, our knowledge of distribution is far from complete. The mammals on many small islands have never been surveyed, those on many moderately large islands are poorly known, and many mountain ranges on the largest islands remain unexplored. New distributional records are discovered by virtually every regional survey, particularly among the more poorly known taxa (especially bats and rodents). Further field work is essential to determine the distributions and habitat requirements of many species, to document the faunas of the smaller island groups, and to carry out the basic taxonomic studies that are necessary to determine species limits and to discover new species.

The distribution of marine mammals in this synopsis is based on surveys, published records of occurrence, strandings, fishery by-catch, and skeletons found on beaches. Not all of the marine habitats have been surveyed, and thus the absence of records of a given species from any given area may result from lack of surveys rather than real absence. Most surveys have been focused on the waters of the Visayan region such as the eastern Sulu Sea, Tanon Strait, Bohol Sea, Panay Gulf, and parts of the Visayan Sea. Other areas recently surveyed include the southern Sulu Sea, Davao Gulf, Verde Island Passage, Celebes/Sulawesi Sea, Davao, Babuyan Islands, offshore of Sierra madre, around Palawan, and portions of the South China Sea.

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