ESSAY 3
Island Life along Wallace’ Line: Biogeography and patterns of Endemism in the Philippines Indonesia
Lawrence R. Heaney
When Alfred Russell Wallace published his description of the biogeographic line that now bears his name, he not only described a pattern of diversity and endemism but also made a prediction that deserves mention as one of the first testable biogeographic hypotheses. Wallace knew that the Malay Peninsula, Sumatra, Java, Bali, and Borneo share faunas that are generally similar and that Lombok, Sulawesi, and islands to the east have very different faunas. For example, marsupials live only to the east of the line, tree shrews and apes only to the west. From recent mapping carried out by the British Admiralty, Wallace also knew that the islands to the west (on what we now call the Sunda Shelf) were separated by shallow waters (not more than about 80 meter) but that those to the east were surrounded by water usually more than 200 meters deep. Wallace hypothesized that at some time in the past the land was higher or the water lower by 100 meters or more. This exposed the islands of the shallow Sunda Shelf as a continuous past of the Asian continent. However, the islands to the east remained isoland, with perhaps occasional to New Guinea, which lies still further east (Wallace 1860, 1880).
Wallace was startlingly correct, and his thoughtful observations are essential to anyone striving to understand the complex pattern of biodiversity in the Indo-Pacific. We now know that there were twenty-one or more cycles of continental glacial development during the Pleistocene, the period of more than 2 million years popularly known as the Ice Ages. During this period, the transfer of liquid water from the oceans to solid ice on land resulted in the sea level declines that often exceeded 100 meters. The most recent Glaciation, which peaked about 18000 years ago, dropped sea level to 120 meters below the present level, resulting in exactly what Wallace envisioned: a massive peninsula extending south from Indochina to Borneo and Java, surrounded by deep water (figure 2.4; Heaney 1991a). To the east lay a smaller number of larger island we see today, but these islands remained isolated from one another by deep straits (Heaney 1985, 1986, 1991b). The repeated pattern of periodic connection between some-but not all-of the region’s islands had shaped patterns of distribution and endemism among plants and animals. On Borneo, one of the largest islands in the world (743,000 km), the native, nonflying mammals include about 30 species that are endemic out of 130 (ca. 23 percent); Sumatra has fewer endemic species (about 10 out of 112; 9 percent) and Java fewer still (ca. 8 out of 62; 13 percent; Heaney 1986). Most of the endemic species are found in montane or mossy forest above 1,500 meters (Md. Nor, in press) in contrast, majority of lowland mammals range widely from northwest Sumatra to eastern Borneo. At 125,000 km, Java is the smallest island on the Sunda Shelf with any endemic mammals
Just a short distance away across wallace's Line, things are dramatically different: on Sulawasi, with about seventy species of native nonflying mammals, all but two species are endemic (Musser 1987), and the many small islands east of Java and Sulawesi are rich in endemic species (flannery 1990, 1995). The pattern remains the same in the Philippines, where the island faunas are well known: on the lce Age islands of Greater Mindanao and Greater Luzon, respectively, 79 and 71 percent of their nonflying native mammals are endemic (figure 2.5; Heaney et al. 1999; Heaney and Regalado 1998), and even the medium-sized islands such as Mindoro (9,800 km) have 45 to 50 percent endemism. Sibuyan, an island of 463 km, has four endemic nonflying mammals (plus one bat; Goodman and lngle 1993; Heaney et al. 1999), and Camiguin, with an area of 265 km, has two endemic species (Heaney and Tabaranza 1997). We now recognize that every islands that remained isolated during the Pleistocene periods of low sea is a unique center of biological diversity (Heaney and Regalado 1998). Species richness remains highly correlated with island area, so small islands have fewer species than large ones, but each lce Age island is a distinctive center of biodiversity.
On the other hand, islands that were connected during the period of low sea level have highly similar faunas. All the islands that made up Greater Luzon Island share the same mammal fauna; there are no differences in the lowland fauna. Only the high elevations on Luzon have localized endemic species, where mossy forest habitats are isolated from one another (Rickart et al. 1998). The same is true, with only a few exceptions, throughout the rest of the Philippines and indonesia.
These same patterns of endemism hold strongly among reptiles and amphibians in the philippines (Alcala and Brown 1998), where endemism percentages can run even higher than among the nonflying mammals. Bats and birds show similar patterns to herpetofauna but with some interesting differences. The places where endemic species occur are similar. but the percentage of endemism is much less: usually 10-20 percent rather than 40-80 percent (Heaney 1991b; Stattersfield et al. 1998). The reasons seem clear: animals that are able to fly can maintain gene flow across permanent sea channels whereas nonflying animals cannot (Peterson and Heaney 1993). Thus, birds and bats are diverse and widespread, but greater degrees of isolation are needed to form distinct species than among the nonflying mammals, reptiles, or amphibians. lnvertebrates such as butterflies in this region show patterns similar to those of birds and bats, confirming the observations based on vertebrates (Holloway 1987, 1998).
Much remains to be learned of details and exceptions, especially concerning the biogeographic processes by which the patterns are produced (whitmore 1987;hall and hollway 1998). however, there is now a clear and consistent guide to the centers of endemism in the vast archipelagoes that lie south of indochina and east to New Guinea. islands that have been connected to one another during periods of low sea level share very similar faunas, whereas each island (or set of islands)that remained isolated is a unique center of endemism. on an island or set of islands that has never been surveyed, chances are that endemic species will be found if a survey were conducted. this was the case for Sibuyan, where mammals were almost undocumented and where field studies were predicted to turn up new endemics. not surprisingly, recent field investigations discovered five new mammal species (goodman and lngle 1993; heaney et al. 1999).
There is one notable exception to this pattern, however: natural habitat must still be present for endemic species to be present. At the same time that Sibuyan and Camiguin were investigated, Siquijor, an island of similar size (253 km^2) off the southeast tip of Greater Negros-Panay, was also surveyed. No endemic mammals were found, nor was any of the old-growth rain forest that once covered the island (Lepiten 1997). if any endemic mammals once lived there-or reptiles or amphibians-loss of habitat has resulted in their extinction. Endemic mammals on other island in the Philippines, the Lesser Sunda Islands, and the Moluccas may have suffered the same fate (Flannery 1990; Heaney and Regalado 1998; Kitchener et al. 1990). In the Philippines, old-growth for-est has declined from originally covering about 97 percent of the country to 6-8 percent today, resulting in the country being listed as one of the hottest hotspots (Mittermeier et al.1999). Whereas some islands in Indonesia (such as Sulawesi) still have fairly good montane forest cover, other islands such as in the Moluccas and the Lesser Sundas have been severely deforested.
This combination of factors makes conservation of biodiversity in the islands of australasia especially challenging. first, a few large parks will miss much of the biodiversity because much of that biodiversity is scattered among many small centers of endemism, either in isolated mountain ranges or on scattered oceanic islands. second, many of the potential centers of endemism have never been inventoried and can thus easily by overlooked. and third, for some of the smaller centers of endemism, it may be too late: when the last of the mature rain forest disappears, so does the endemic biota. quick action is needed at all levels.
เรียงความ 3เกาะชีวิตตาม Wallace' บรรทัด: Biogeography และรูปแบบของ Endemism ในอินโดนีเซียฟิลิปปินส์ลอว์เรนซ์อาร์มุสฮีนีย์เมื่ออัลเฟรดรัสเซล Wallace เผยแพร่เขาอธิบายบรรทัด biogeographic หมีตอนนี้ ชื่อของเขา เขาไม่เพียงอธิบายรูปแบบของความหลากหลายและ endemism ได้ทำการคาดการณ์ที่สมควรกล่าวถึงเป็นหนึ่งในสมมุติฐาน biogeographic testable แรก Wallace รู้ว่า คาบสมุทรมลายู เกาะสุมาตรา ชวา บาหลี กับบอร์เนียวร่วม faunas ที่คล้ายกันโดยทั่วไป และลอมบอก Sulawesi และหมู่เกาะฝั่งตะวันออกมี faunas แตกต่างกันมาก ตัวอย่าง marsupials อาศัยอยู่เฉพาะในภาคตะวันออกของบรรทัด แผนภูมิ shrews และลิงเท่านั้นไปทางตะวันตก จากล่าสุดแมปที่ดำเนินการ โดยแอดไมรัลตี้อังกฤษ Wallace ยังรู้ว่า ที่เกาะทางตะวันตก (ตามที่เราตอนนี้โทรชั้นซุนดา) ถูกคั่น ด้วยตื้น (ประมาณไม่เกิน 80 เมตร) แต่ว่า ที่ฝั่งตะวันออกถูกล้อมรอบ ด้วยน้ำปกติมากกว่า 200 เมตรลึก Wallace ตั้งสมมติฐานว่าที่บางครั้งในอดีตแผ่นดินได้สูง หรือน้ำต่ำกว่า 100 เมตรหรือมากกว่านั้น นี้สัมผัสหมู่เกาะซันดาชั้นตื้นเป็นอดีตอย่างต่อเนื่องของทวีปเอเชีย อย่างไรก็ตาม หมู่เกาะฝั่งตะวันออกยังคง isoland ด้วยเป็นครั้งคราวอาจจะนิวกินี ที่อยู่ต่อไปยังตะวันออก (Wallace 1860, 1880)Wallace was startlingly correct, and his thoughtful observations are essential to anyone striving to understand the complex pattern of biodiversity in the Indo-Pacific. We now know that there were twenty-one or more cycles of continental glacial development during the Pleistocene, the period of more than 2 million years popularly known as the Ice Ages. During this period, the transfer of liquid water from the oceans to solid ice on land resulted in the sea level declines that often exceeded 100 meters. The most recent Glaciation, which peaked about 18000 years ago, dropped sea level to 120 meters below the present level, resulting in exactly what Wallace envisioned: a massive peninsula extending south from Indochina to Borneo and Java, surrounded by deep water (figure 2.4; Heaney 1991a). To the east lay a smaller number of larger island we see today, but these islands remained isolated from one another by deep straits (Heaney 1985, 1986, 1991b). The repeated pattern of periodic connection between some-but not all-of the region’s islands had shaped patterns of distribution and endemism among plants and animals. On Borneo, one of the largest islands in the world (743,000 km), the native, nonflying mammals include about 30 species that are endemic out of 130 (ca. 23 percent); Sumatra has fewer endemic species (about 10 out of 112; 9 percent) and Java fewer still (ca. 8 out of 62; 13 percent; Heaney 1986). Most of the endemic species are found in montane or mossy forest above 1,500 meters (Md. Nor, in press) in contrast, majority of lowland mammals range widely from northwest Sumatra to eastern Borneo. At 125,000 km, Java is the smallest island on the Sunda Shelf with any endemic mammalsJust a short distance away across wallace's Line, things are dramatically different: on Sulawasi, with about seventy species of native nonflying mammals, all but two species are endemic (Musser 1987), and the many small islands east of Java and Sulawesi are rich in endemic species (flannery 1990, 1995). The pattern remains the same in the Philippines, where the island faunas are well known: on the lce Age islands of Greater Mindanao and Greater Luzon, respectively, 79 and 71 percent of their nonflying native mammals are endemic (figure 2.5; Heaney et al. 1999; Heaney and Regalado 1998), and even the medium-sized islands such as Mindoro (9,800 km) have 45 to 50 percent endemism. Sibuyan, an island of 463 km, has four endemic nonflying mammals (plus one bat; Goodman and lngle 1993; Heaney et al. 1999), and Camiguin, with an area of 265 km, has two endemic species (Heaney and Tabaranza 1997). We now recognize that every islands that remained isolated during the Pleistocene periods of low sea is a unique center of biological diversity (Heaney and Regalado 1998). Species richness remains highly correlated with island area, so small islands have fewer species than large ones, but each lce Age island is a distinctive center of biodiversity.On the other hand, islands that were connected during the period of low sea level have highly similar faunas. All the islands that made up Greater Luzon Island share the same mammal fauna; there are no differences in the lowland fauna. Only the high elevations on Luzon have localized endemic species, where mossy forest habitats are isolated from one another (Rickart et al. 1998). The same is true, with only a few exceptions, throughout the rest of the Philippines and indonesia.These same patterns of endemism hold strongly among reptiles and amphibians in the philippines (Alcala and Brown 1998), where endemism percentages can run even higher than among the nonflying mammals. Bats and birds show similar patterns to herpetofauna but with some interesting differences. The places where endemic species occur are similar. but the percentage of endemism is much less: usually 10-20 percent rather than 40-80 percent (Heaney 1991b; Stattersfield et al. 1998). The reasons seem clear: animals that are able to fly can maintain gene flow across permanent sea channels whereas nonflying animals cannot (Peterson and Heaney 1993). Thus, birds and bats are diverse and widespread, but greater degrees of isolation are needed to form distinct species than among the nonflying mammals, reptiles, or amphibians. lnvertebrates such as butterflies in this region show patterns similar to those of birds and bats, confirming the observations based on vertebrates (Holloway 1987, 1998).
Much remains to be learned of details and exceptions, especially concerning the biogeographic processes by which the patterns are produced (whitmore 1987;hall and hollway 1998). however, there is now a clear and consistent guide to the centers of endemism in the vast archipelagoes that lie south of indochina and east to New Guinea. islands that have been connected to one another during periods of low sea level share very similar faunas, whereas each island (or set of islands)that remained isolated is a unique center of endemism. on an island or set of islands that has never been surveyed, chances are that endemic species will be found if a survey were conducted. this was the case for Sibuyan, where mammals were almost undocumented and where field studies were predicted to turn up new endemics. not surprisingly, recent field investigations discovered five new mammal species (goodman and lngle 1993; heaney et al. 1999).
There is one notable exception to this pattern, however: natural habitat must still be present for endemic species to be present. At the same time that Sibuyan and Camiguin were investigated, Siquijor, an island of similar size (253 km^2) off the southeast tip of Greater Negros-Panay, was also surveyed. No endemic mammals were found, nor was any of the old-growth rain forest that once covered the island (Lepiten 1997). if any endemic mammals once lived there-or reptiles or amphibians-loss of habitat has resulted in their extinction. Endemic mammals on other island in the Philippines, the Lesser Sunda Islands, and the Moluccas may have suffered the same fate (Flannery 1990; Heaney and Regalado 1998; Kitchener et al. 1990). In the Philippines, old-growth for-est has declined from originally covering about 97 percent of the country to 6-8 percent today, resulting in the country being listed as one of the hottest hotspots (Mittermeier et al.1999). Whereas some islands in Indonesia (such as Sulawesi) still have fairly good montane forest cover, other islands such as in the Moluccas and the Lesser Sundas have been severely deforested.
This combination of factors makes conservation of biodiversity in the islands of australasia especially challenging. first, a few large parks will miss much of the biodiversity because much of that biodiversity is scattered among many small centers of endemism, either in isolated mountain ranges or on scattered oceanic islands. second, many of the potential centers of endemism have never been inventoried and can thus easily by overlooked. and third, for some of the smaller centers of endemism, it may be too late: when the last of the mature rain forest disappears, so does the endemic biota. quick action is needed at all levels.
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