Seasonal species richness of birds on the world's islands and its geographical correlates

Migratory birds occur on islands during different seasons of the year, which results in seasonal variation in species richness. These patterns and their geographical correlates have not been examined. We used 20 years of bird observations on 690 islands to examine how seasonal species richness estimates vary as a function of island area, isolation, and latitude. Species richness was highest on islands within the mid-latitudes of the Northern Hemisphere during migration and on islands within tropical latitudes during the non-breeding season. Area defined positive, non-linear relationships with species richness across seasons, with the steepest slopes occurring with islands >1,100 km2. Distance to mainland defined negative, non-linear relationships with species richness across seasons, with the strongest slopes occurring with islands located >150 km from the mainland. Species-area relationships were weakest for the most remote islands and strongest for islands at intermediate distances to the mainland. Intermediate proximity to other islands was a poor predictor of species richness. Our findings emphasize the presence of seasonally dynamic relationships, the enhanced role of evolutionary processes on larger islands, the unique ecology of the world's most remote islands, and the importance of islands as stopover sites and wintering grounds for migratory bird species.

候鸟于一年中的不同季节栖息于各类岛屿，由此导致岛屿物种丰富度呈现季节性波动。目前尚未有研究对这类分布模式及其地理关联特征展开探讨。本研究依托690座岛屿长达20年的鸟类观测数据，探究了岛屿物种丰富度的季节性估算值如何随岛屿面积、隔离度以及纬度发生变化。研究结果显示，在迁徙季，北半球中纬度岛屿的物种丰富度达到峰值；而在非繁殖季，热带纬度岛屿的物种丰富度最高。各季节中，岛屿面积与物种丰富度均呈正相关的非线性关系，当岛屿面积大于1100平方千米时，二者的斜率最为陡峭。岛屿与大陆的距离与物种丰富度则呈负相关的非线性关系，当岛屿距大陆超过150千米时，二者的斜率强度达到最大。物种-面积关系在最偏远的岛屿上表现最弱，而在距大陆中等距离的岛屿上表现最强；与其他岛屿的中等邻近程度，无法有效预测物种丰富度。本研究结果强调了候鸟分布关系的季节性动态特征、大型岛屿上演化过程的增强作用、全球最偏远岛屿的独特生态学属性，以及岛屿作为候鸟迁徙中途停歇地与越冬地的重要性。