A framework for monitoring the status of populations: An example from wader populations in the East Asian–Australasian flyway

The loss of biodiversity is an ongoing problem and it is essential that a framework is established for revealing the status, identifying threats and monitoring future changes of populations. This study focuses on wader populations in the East Asian–Australasian flyway, and aims to develop a three-step framework for monitoring the status of populations. First, population changes of waders are quantified by estimating population indices from nationwide survey data in Japan between 1975 and 2008. Second, species characteristics shared by declining waders are identified using a phylogenetic comparative method. Finally, based on the revealed characteristics of declining species, composite indices are created for monitoring changes in wader communities in the East Asian–Australasian flyway. The estimated population indices revealed that 12 species out of 41, and 16 out of 42 have declined significantly during spring and autumn migration, respectively, in at least one of the past 10, 20 or 30 year-periods. Phylogenetic comparative analysis revealed that both the use of rice fields and dependence on the Yellow Sea negatively affected the population trends of waders. These results are consistent with the hypothesized negative impact of agricultural intensification caused by land consolidation in Japanese rice fields, and habitat loss and/or degradation in the Yellow Sea caused by the rapid growth of populations and economies in China and South Korea. The framework developed in this study can be applied to a wide range of species, and should play an important role in monitoring population trends and identifying threats to those species in future.