ABSTRACT

Island ecosystems can be severely affected by climate change as they provide limited opportunities for species to track their habitat. Studying the population dynamics of keystone species from these ecosystems can shed a light on climate – ecosystem interactions. Southern beeches are such keystone species in New Zealand with beech forests constituting the most abundant forest cover on the two main islands. Here we use 2.4 kilobase pairs of chloroplast genetic markers from four species of southern beech across their geographic distribution to help elucidate the Pleistocene history of New Zealand forests, and the processes that led to the present-day distribution of southern beech diversity. Broadly concordant phylogeographic patterns were observed across all beech species analysed. The centre of genetic diversity in silver beech was in the northern South Island, with unique haplotypes in the southern South Island, and southern and northern North Island, separated by known ‘beech gaps’. Significantly less genetic diversity was evident in the subgenus Fuscospora (red, hard, black/mountain beech). All three species shared a single haplotype in the southern South Island, and a unique haplotype north of the central South Island ‘beech gap’. Our study indicates that the present-day distribution of southern beech diversity in New Zealand is largely a result of Plio-Pleistocene environmental changes, with survival in cryptic southern South Island and multiple North Island in situ microrefugia throughout recent glacial cycles. By contrast, the northern South Island was likely the only New Zealand region that supported large (silver) beech populations throughout the Pleistocene. With beech species in New Zealand being keystone forest species, the distribution of the genus throughout the Pleistocene provides a proxy for forest cover at different times. It helps understand the ecological challenges the New Zealand forest fauna and flora were exposed to during the climate oscillations of the ice ages.

摘要

由于岛屿生态系统为物种追踪生境提供了有限的机会，因此它们可能会受到气候变化的严重影响。研究来自这些生态系统的关键物种的种群动态可以阐明气候-生态系统的相互作用。南部山毛榉是新西兰的主要树种，山毛榉森林构成了两个主要岛屿上森林覆盖率最高的地区。在这里，我们使用来自南山毛榉的四种物种的2.4千碱基对的叶绿体遗传标记，跨其地理分布，以帮助阐明新西兰森林的更新世历史，以及导致当今南山毛榉多样性分布的过程。在所分析的所有山毛榉物种中均观察到大致一致的植物学模式。银山毛榉的遗传多样性中心在南岛北部，在南岛南部以及北岛南部和北部具有独特的单倍型，被已知的“山毛榉缺口”隔开。该亚属中的遗传多样性明显较少Fuscospora（红色，坚硬，黑色/山毛榉）。这三个物种在南岛南部共享一个单倍型，在南岛中部“山毛榉缺口”北部共享一个独特的单倍型。我们的研究表明，当今新西兰南部山毛榉多样性的分布在很大程度上是上新世更新世环境变化的结果，在隐秘的南部南岛和多个北岛原地生存整个最近的冰川周期存在微反射。相比之下，南岛北部可能是唯一在整个更新世期间支撑大量（银色）山毛榉种群的新西兰地区。由于新西兰的山毛榉树种是主要的森林树种，整个更新世的属分布在不同时间提供了森林覆盖率的代名词。它有助于了解在冰河时期的气候振荡期间新西兰森林动植物所面临的生态挑战。