東亞至紐澳的鳥種遷徙比例、遷徙距離、 及島嶼生物地理界線

Abstract

巨觀生態學著眼於大尺度的空間分布模式，相關研究能為生物地理學的研究主題提供重要證據，兩者相輔相成。鳥類遷徙涉及大尺度的空間分布，其與環境因子及鳥類本身生物特徵的相關性長久以來受人關注，而且東亞島嶼間的生物地理界線亦是生物地理學的長久議題。本研究以東經 70 度至東經180度，北緯 90 度至南緯 90 度為範圍，計算繁殖地位於此範圍內的候鳥鳥種種數占所有繁殖鳥種種數的比例，並檢驗其與五種環境因子的相關性。五種環境因子包含氣溫的季節差異、初級生產力的季節差異、雨量的季節差異，島嶼疏離指數、以及海拔高度差異。研究結果顯示，鳥種遷徙比例從赤道到兩極呈上升趨勢，南北半球的鳥種遷徙比例不同，東亞大陸與島嶼的鳥種遷徙比例差異較小。氣溫的季節差異是影響鳥種遷徙的主要環境因子，代表鳥類能量支出，因高緯度繁殖地在非繁殖季時氣溫下降，鳥類若選擇非繁殖季時留在此地，需支出較多能量來維持固定體溫。相較之下，代表能量取得的初級生產力的季節差異與其他環境因子的影響間接且有限。此外，南半球的鳥種遷徙比例較北半球低，可能是澳洲大陸與其他大陸的長期隔離，該大陸溫和的古氣候與當代氣候所造成。目前全球氣候暖化，本研究結果強調氣候暖化對鳥類遷徙的影響，並為未來相關研究奠基。 鳥種遷徙距離是衡量遷徙行為整體趨勢的重要指標，與候鳥鳥種的能量收支息息相關。本研究根據繁殖地位於東經 70 度至東經180度，北緯 90 度至南緯 90 度的586種候鳥，根據其全球分布範圍，計算其繁殖地與非繁殖地中點的最短距離，呈現多種鳥種遷徙距離的整體趨勢，並以體重、食性做為能量支出與收入的指標，檢驗其與鳥種遷徙距離的相關性。研究結果顯示，40%的鳥種遷徙距離為2,000-4,000公里，鳥種遷徙距離較長者為鹬鴴目、鶺鴒科、以及燕科。鳥種遷徙距離與標準化體重呈駝峰狀相關。以每種候鳥的平均身長做為遷徙距離的計算單位，鳥種遷徙身長與體重呈負相關。鳥種遷徙距離實際值顯著偏離模型估計值。非燕雀目與燕雀目的肉食鳥種的遷徙距離皆顯著高於植食鳥種。總之，鳥種遷徙距離可用體重估計，但是估計值與實際值差異相當大，顯示估計模型需針對鳥類進行調整。鳥種遷徙距離也與食性相關，顯示遷徙行為與生態系不同營養階層所需的能量差異具關連性。相較多數文獻從外在環境的角度探討遷徙行為與能量的關係，本研究從生物特徵的角度切入，為遷徙行為整體趨勢提供新的詮釋視野。 生物地理區的研究歷史已超過150年，其中又以東亞島嶼之間的生物地理界線為最主要的研究焦點。本研究針對北起庫頁島，東至新幾內亞，橫跨古北區、東洋區、澳洲區的主要島嶼，進行整合統計檢測，根據此範圍內的所有陸域繁殖鳥種分布範圍，計算島嶼間的辛普森相異度指標，進行集群分析及非度量多維尺度排序來劃分生物地理界線。研究結果顯示，東洋區與澳洲區的生物地理界線應落於小巽他群島與摩鹿加群島間海峽，其餘分界與華萊士線相同，因小巽他群島繁殖鳥類相與東洋區較為相似。巴拉望與婆羅洲的繁殖鳥類相應屬於不同的生物地理次區，因巴拉望繁殖鳥類相與婆羅洲較不相似。古北區與東洋區的界線為臺灣與菲律賓間海峽。琉球群島、北海道的繁殖鳥類相，分別與九州、本州等生物地理次區的繁殖鳥類相差異較大。更新世海水面上昇形成的海峽障礙可能造成現今界線兩側的繁殖鳥類相差異，成為以上分界的主要根據。在全球大陸為範圍的生物地理研究中，本研究聚焦島嶼間生物地理界線，提供一個以島嶼為主體的特殊觀點。

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.