Newmark W D
Nature. 1987;325(6103):430-2. doi: 10.1038/325430a0.
In recent years, a number of authors have suggested several geometric principles for the design of nature reserves based upon the hypothesis that nature reserves are analogous to land-bridge islands. Land-bridge islands are islands that were formerly connected to the mainland and were created by a rise in the level of the ocean. Land-bridge islands are considered supersaturated with species in that the ratio of island to mainland species numbers is higher than expected from the area of the island. As a result, the rate of extinction should exceed the rate of colonization on a land-bridge island, resulting in a loss of species that is suggested to be related to the size and degree of isolation of the island. If nature reserves are considered to be similar to land-bridge islands, because most are slowly becoming isolated from their surroundings by habitat disturbance outside the reserves, several predictions follow. First, the total number of extinctions should exceed the total number of colonizations within a reverse; second, the number of extinctions should be inversely related to reserve size; and third, the number of extinctions should be directly related to reserve age. I report here that the natural post-establishment loss of mammalian species in 14 western North American national parks is consistent with these predictions of the land-bridge island hypothesis and that all but the largest western North American national parks are too small to retain an intact mammalian fauna.
近年来，一些作者基于自然保护区类似于陆桥岛的假设，提出了若干自然保护区设计的几何原理。陆桥岛是曾经与大陆相连、后因海平面上升而形成的岛屿。陆桥岛被认为物种超饱和，因为岛屿与大陆物种数量之比高于根据岛屿面积预期的比例。因此，陆桥岛上的灭绝速率应超过定殖速率，导致物种丧失，这被认为与岛屿的大小和隔离程度有关。如果自然保护区被认为类似于陆桥岛，由于大多数保护区正因保护区外的栖息地干扰而逐渐与周围环境隔离，那么会有几个预测结果。第一，保护区内的灭绝总数应超过定殖总数；第二，灭绝数量应与保护区面积成反比；第三，灭绝数量应与保护区建立时间成正比。我在此报告，北美西部14个国家公园中哺乳动物物种在建立后的自然损失与陆桥岛假说的这些预测相符，而且除了北美西部最大的国家公园外，其他所有公园都太小，无法保留完整的哺乳动物群落。
