三種闊尾海蛇棲地選擇

Abstract

了解動物的偏好棲地和分布模式，不只要考慮環境和生態的外在因子，動物的內部生理條件也是要考量的重要因素。已知三種兩棲性的闊尾海蛇(Laticauda)都需要喝淡水，而其在陸地上水份散失的速率以闊帶青斑海蛇(L. semifasciata)最高，其次為黑唇青斑海蛇(L. laticaudata) ，黃唇青斑海蛇(L. colubrina)最低。本實驗欲探討三種海蛇在生理適應上的差異是否反映在棲地的選擇上。我於2009年7月至2010年9月在野外觀察海蛇實際利用的棲地和測量各種棲地因子。結果顯示，三種海蛇的陸棲程度為黃唇青斑海蛇最高，在陸地上被發現的比例最高，可攀爬的坡度最陡，也會爬行至最內陸的位置。而黑唇青斑海蛇陸棲程度介於兩者之間，闊帶青斑海蛇的海棲程度最高，海中發現的比例遠高於陸地，只能攀爬較為平緩的礁岸，通常離岸不超過兩公尺。而三種海蛇在棲地利用上都明顯偏好有淡水水源且地形為高位礁石的棲地，然而三種海蛇的棲地利用仍有些差異，黃唇青斑海蛇利用的棲的類型最為廣泛，闊帶青斑海蛇利用的棲地較為專一，且海蝕溝的溝口水深需較大，溝口底部礁石在退潮時不能露出水面，否則闊帶青斑海蛇便不會出現在此類棲地。

Animal habitat preference and distribution pattern are frequently affected by environmental and ecological factors. Other than these, the internal physiological condition of the animal may also be important. It is known that three sea kraits (Laticauda spp.) require fresh water, and the evaporative water loss on the land is different among these 3 species. L. semifasciata has the greatest water loss rate while L. colubrina has the smallest water loss rate and L. laticaudata was in between. In this study, I aimed to investigate habitat selection of these sea kraits, and checked if it was associated with their different physiological adaptation. In July 2009 to September 2010, I recorded the number of each species and some habitat parameters on Orchid Island. The results showed that L. colubrina had the highest terrestrial tendency; they were found most frequently on land, they might climb the most steep slope and get inland the farthest distance. In contrast, L. semifasciata exhibited the highest marine tendency; they were found in the sea more frequently than on land, they could climb only on gentle slope and get inland at most two meters offshore. All of the sea kraits preferred the habitat with high coral reef and fresh water. Nevertheless, the habitat selections among three sea snakes may still be different. L. colubrina were found in more different types of habitats while L. semifasciata were specialized on fewer types of habitats.