臺灣紫斑蝶越冬棲地之環境特徵

Abstract

每年冬天數百萬隻紫斑蝶(Euploea spp.)從臺灣各處一同遷徙到南臺灣的紫蝶幽谷越冬。雖然紫斑蝶為廣泛分布於東南亞熱帶地區的蝴蝶，但是大規模的群聚越冬現象目前只在臺灣發現；重要的是此種越冬型蝶谷在世界上極為罕見。雖然目前臺灣已知的紫蝶幽谷約三十多處，但對於紫蝶幽谷的成因還尚未清楚；此外在人為開發與氣候變遷下，對於臺灣紫斑蝶族群遷徙的影響仍是未知。因此本研究將探討1.紫斑蝶越冬棲地選擇條件，以便進行紫斑蝶保育，2. 推測在氣候變遷下，紫斑蝶的遷徙行為與臺灣其他可做為潛在越冬谷的谷地。 本研究自2015年11月起至2016年三月，於茂林國家風景區針對紫斑蝶蝶谷進行實地調查，並於2016年11月起至2017年三月間，在高雄縣茂林區的低海拔山區中隨機設微氣候站，以便收集當地的微氣候資料。實地調查所收集的資料以ArcGIS做蝶谷分布並與不同環境因子做疊圖分析，遙測則做為輔助工具。所有分析結果與往年紫斑蝶越冬蝶谷地理資訊資料、氣象站資料進行比較、核對，去推測紫斑蝶越冬蝶谷的成因。 巨觀來看，越冬蝶谷大多有以下特色：1.位於海拔五百公尺以下，且坡度小於45度的山凹處 2.主要位在南向坡、谷口朝南，而北向坡的越冬蝶谷則須在向陽面 3.東側有兩千公尺以上的高山為屏障 4.越冬期間風向以北北東為主，而谷內平均風速小於2.0m/s 5.谷內冬季日均溫約在16-28℃ 6.相對濕度約70%。微觀來看，茂林區內五個主要越冬蝶谷之間的月平均溫度並無明顯差異，然而五個蝶谷中的十五個微氣候站(不同生態地理環境)，日夜溫差有著顯著差異 (p<0.001)，而森林密度除了影響林間的溫差變化程度外也影響林間的光照度。 綜合以上結果，一個合適的越冬棲地有以下特徵：位於海拔500公尺以下、坡度小於45度的深谷中、谷口朝南。林相為森林密度高的原始混合林。谷內的溫差變化小、平均溫度大於臨界死亡溫度且無風干擾、光強度弱的乾溪溝環境。

During winter, Purple Crow butterfly (Euploea spp.) forms colonies in the overwintering site covered with broad-leaf mixed forests in southern Taiwan, where the forests act as shelters to protect the butterflies from Northeast monsoon. However, the ecological factors and the interactions among these factors that affect Purple Crow butterfly on choosing the overwintering site are not well understood. In this study, I conducted landscape scale study of various kinds of overwintering sites at Maolin National Scenic Area from November 2015 to March 2016 and microhabitat study in Maolin District from November 2016 to March 2017. To figure out factors which contribute to the formation of the overwintering site, I overlaid the site locations with layers including climatic and topographic variables on ArcGIS. All data were compared with past overwintering sites (from 1980s to 2015) and analyzed by using R versions 3.3.0. The landscape features indicated that most of the overwintering sites are located in the mountain concave on the south facing slope with slope no bigger than 45° and the altitude was under five hundred meters above the sea level. Second, the average winter temperature in overwintering sites temperature is above the critical freezing temperature 4°C and the relative humidity was 70%. Finally, the main wind direction during the winter period was North North-East with the average wind speed in the valleys no larger than 2.0 m/s. As for microhabitat features, the narrow daily temperature range is the main factor contributing to the formation of the overwintering site. Furthermore, a suitable overwintering site is covered with dense mixed forest without wind disturb and the temperature must be above critical freezing temperature.