Department of Anthropology, University of Zürich, Winterthurerstr 190, 8057, Zürich, Switzerland.
Fakultas Biologi, Universitas Nasional, Jln Sawo Manila, Jakarta, 12520, Indonesia.
J Hum Evol. 2018 Dec;125:38-49. doi: 10.1016/j.jhevol.2018.09.004. Epub 2018 Oct 25.
Orangutans (Pongo spp.) are reported to have extremely slow life histories, including the longest average interbirth intervals of all mammals. Such slow life history can be viable only when unavoidable mortality is kept low. Thus, orangutans' survivorship under natural conditions is expected to be extremely high. Previous estimates of orangutan life history were based on captive individuals living under very different circumstances or on small samples from wild populations. Here, we combine birth data from seven field sites, each with demographic data collection for at least 10 years (range 12-43 years) on wild orangutans to better document their life history. Using strict criteria for data inclusion, we calculated infant survival, interbirth intervals and female age at first reproduction, across species, subspecies and islands. We found an average closed interbirth interval of 7.6 years, as well as consistently very high pre-weaning survival for males and females. Female survival of 94% until age at first birth (at around age 15 years) was higher than reported for any other mammal species under natural conditions. Similarly, annual survival among parous females is very high, but longevity remains to be estimated. Current data suggest no major life history differences between Sumatran and Bornean orangutans. The high offspring survival is remarkable, noting that modern human populations seem to have reached the same level of survival only in the 20th century. The orangutans' slow life history illustrates what can be achieved if a hominoid bauplan is exposed to low unavoidable mortality. Their high survival is likely due to their arboreal and non-gregarious lifestyle, and has allowed them to maintain viable populations, despite living in low-productivity habitats. However, their slow life history also implies that orangutans are highly vulnerable to a catastrophic population crash in the face of drastic habitat change.
猩猩（Pongo spp.）的生活史非常缓慢，包括所有哺乳动物中最长的平均生育间隔。这种缓慢的生活史只有在不可避免的死亡率保持较低水平时才可行。因此，在自然条件下，猩猩的存活率应该非常高。以前对猩猩生活史的估计是基于生活在非常不同环境中的圈养个体或来自野生种群的小样本。在这里，我们结合了来自七个野外研究点的数据，每个研究点都有至少 10 年的人口数据收集（范围为 12-43 年），以便更好地记录它们的生活史。我们使用严格的数据纳入标准，计算了跨物种、亚种和岛屿的婴儿存活率、生育间隔和雌性首次繁殖年龄。我们发现平均封闭生育间隔为 7.6 年，雄性和雌性的幼仔在哺乳期前的存活率一直非常高。雌性在首次生育（约 15 岁）前的存活率为 94%，高于任何其他在自然条件下的哺乳动物物种。同样，经产雌性的年存活率也非常高，但长寿仍有待估计。目前的数据表明，苏门答腊猩猩和婆罗洲猩猩之间没有主要的生活史差异。后代的高存活率引人注目，值得注意的是，现代人类种群似乎直到 20 世纪才达到相同的存活率水平。猩猩缓慢的生活史说明了，如果类人猿的 Bauplan 暴露在低不可避免的死亡率下，会有什么样的结果。它们的高存活率可能归因于它们的树栖和非群居生活方式，这使它们能够在低生产力的栖息地中维持有活力的种群。然而，它们缓慢的生活史也意味着，猩猩在面对剧烈的栖息地变化时，极易遭受灾难性的种群崩溃。
