| Summary: | 博士 === 國立臺灣大學 === 森林環境暨資源學研究所 === 102 === Macroecology features large-scale spatial patterns, and many studies in this discipline have provided important evidences to biogeography. Bird migration and its relationship with the contemporary environment and species biological traits, together with biogeographic boundaries among East Asian islands, have been of long-term interest. I calculated the avian migration ratio in the lands from 70°E to 180°E and from 90°N to 90°S. Its relationships with the contemporary environment was examined, including annual ranges of ambient temperature, primary productivity (surrogated by Enhanced Vegetation Index), precipitation, island isolation, and elevational range. In results, the avian migration ratio generally increased from the equator to the poles, with great hemispheric variations but minimal continent-island differences. Seasonality of ambient temperature, which represents energy expenditure of birds, was the environmental factor determining bird species migration. Comparatively, Seasonality of primary productivity, which represents energy intake of birds, and the other environmental factors have indirect and limited influence. Besides, the avian migration ratio was relatively low in the Southern Hemisphere. The difference between the Northern and Southern Hemispheres can be attributed to paleogeographic isolation, mild paleoclimate, and benign contemporary environment in Australia. The findings highlight our concern with the impacts of global warming on bird migration.
Migration distance is also an important measure for the overall pattern of bird species migration. It is highly related to energy intake and expenditure. I examined the overall pattern of the migration distance, based on 586 bird species breeding in the lands from 70°E to 180°E and 90°N to 90°S. The migration distance was calculated as the shortest distance between midpoints of the global breeding and non-breeding ranges. Besides, I assessed the relationship between and the migration distance and energy-surrogating biological attributes, body mass and diet. In results, 40% of the bird species featured migration distance from 2,000 to 4,000 km. Taxa with higher migration distance were Charadriiformes, Motacillidae, and Hirundinidae. The relationship between the migration distance and the normalized body mass was hump-shaped. The average body length of migratory species, another distance measure, was negatively correlated with the body mass. The observed migration distance significantly differed from the model. The migration distance of carnivores was significantly higher than that of herbivores. In sum, the migration distance of birds can be estimated by the body mass. However, large difference between the estimated and the observed values suggests model modification for birds. Besides, the migration distance seems to be related to diet. This links migration behavior with different energy intake in trophic levels in the ecosystem. As most studies have related migration to energy in terms of the external environment, this study provides a novel viewpoint for the overall pattern of bird migration studies in terms of biological attributes.
Biogeographic regions have attracted study interest for over 150 years, and one of the major focuses has been biogeographic boundaries between islands in East Asia. I collectively examined several hypotheses of the biogeographic boundaries based on the avifauna on major islands in East Asia, from Sakhalin to New Guinea, across the Palearctic, the Oriental, and the Australian regions. Based on the species composition of all terrestrial breeding bird species, I calculated Simpson dissimilarity index between the islands and delineated the biogeographic regions, using cluster analysis and Non-metric Multi-Dimension Scaling. In results, the biogeographic boundary between the Oriental and the Australian regions should fall between the Lesser Sunda Islands and Maluku, with the remaining part followed Wallace’s Line, because the breeding avifauna on the Lesser Sunda Islands was of strong Oriental affinity. Palawan and Borneo should be classified into different biogeographic sub-regions, because the breeding avifauna on Palawan was less similar to that on Borneo. The biogeographic boundary between the Palearctic and the Oriental regions should be located along the strait between Taiwan and the Philippines. The Ryukyu Islands and Kyushu may be classified into different biogeographic sub-regions, as well as Hokkaido and Honshu. These biogeographic boundaries may be accounted for by different breeding avifauna on the islands. The difference may result from ocean barriers in consequence of sea level rise during the Pleistocene. As most studies have focused on the scale of global continents, this study examined the biogeographic boundaries between islands and provides a unique viewpoint to the delineation of biogeographic regions.
|
|---|
