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.

候鸟在一年中的不同季节造访岛屿，进而引发物种丰富度的季节性变化。目前尚未有研究对这类格局及其地理相关性展开系统考察。本研究基于690座岛屿20年的鸟类观测数据，探究了季节尺度下的物种丰富度估算值如何随岛屿面积、隔离程度与纬度变化。
迁徙季时，北半球中纬度岛屿的物种丰富度最高；而非繁殖季，热带纬度岛屿的物种丰富度位居前列。各季节下，岛屿面积与物种丰富度均呈正非线性相关关系，其中斜率最陡的对应面积大于1100平方千米的岛屿。与大陆的距离与物种丰富度呈负非线性相关关系，斜率最大的对应距离大陆超过150千米的岛屿。物种-面积关系在最偏远的岛屿上表现最弱，在与大陆距离中等的岛屿上表现最强。与其他岛屿的中等邻近程度，无法有效预测物种丰富度。本研究结果凸显了物种丰富度的季节动态关联、大型岛屿上演化进程的增强作用、全球最偏远岛屿的独特生态特征，以及岛屿作为候鸟中途停歇地与越冬地的重要意义。