Land-use change interacts with island biogeography to alter bird community assembly

Anthropogenic activities have reshaped biodiversity on islands worldwide. However, it remains unclear how island attributes and land-use change interactively shape multiple facets of island biodiversity through community assembly processes. To answer this, we conducted bird surveys in various land-use types (mainly forest and farmland) using transects on 34 oceanic land-bridge islands in the largest archipelago of China. We found that bird species richness increases with island area and decreases with isolation, regardless of the intensity of land-use change. However, forest-dominated habitats exhibited lower richness than farmland-dominated habitats. Island bird assemblages generally comprised species that share more similar traits or evolutionary histories (i.e., functional and/or phylogenetic clustering) than expected if assemblages were randomly assembled. Contrary to our expectations, we observed that bird assemblages in forest-dominated habitats were more clustered on large and close islands, whereas assemblages in farmland-dominated habitats were more clustered on small islands. These contrasting results indicate that land-use change interacts with island biogeography to alter the community assembly of birds on inhabited islands. Our findings emphasize the importance of incorporating human-modified habitats when examining the community assembly of island biota, and further suggest that agricultural landscapes on large islands may play essential roles in protecting countryside island biodiversity.

人类活动已重塑全球范围内岛屿的生物多样性。然而，岛屿属性与土地利用变化如何通过群落组装过程，共同调控岛屿生物多样性的多个维度，目前仍不明确。为解答这一科学问题，我们在中国最大的群岛中的34个海洋陆桥岛屿上，采用样线法对多种土地利用类型（以森林与农田为主）开展了鸟类调查。研究发现，无论土地利用变化强度如何，鸟类物种丰富度均随岛屿面积增大而升高、随隔离度提升而降低；但以森林为主的生境中，鸟类物种丰富度却低于以农田为主的生境。相较于随机组装的群落，岛屿鸟类群落通常由性状或进化历史更为相似的物种构成，即呈现功能聚类和/或系统发育聚类特征。与我们的预期相悖的是，以森林为主的生境中的鸟类群落在面积更大、隔离度更低的岛屿上聚类程度更高，而以农田为主的生境中的鸟类群落在面积更小的岛屿上聚类程度更高。这些截然不同的研究结果表明，土地利用变化与岛屿生物地理学过程共同作用，改变了人类居住岛屿上的鸟类群落组装模式。本研究结果强调，在探讨岛屿生物群落的组装过程时，纳入人类改造生境的重要性；同时进一步指出，大型岛屿上的农业景观在保护乡村岛屿生物多样性方面或可发挥关键作用。