資源分配因子為競爭或生理限制：以黑唇青斑海蛇為例

Abstract

闊帶海蛇屬(Laticauda )為爬蟲綱蝙蝠蛇科下的一屬，此屬海蛇無法在海中完成其生活史，需要上岸進行產卵、蛻皮或消化食物等活動，利用此特性，我們可以於夜晚時刻在岸邊發現牠們的蹤跡。本研究以日本沖繩地區只有黑唇青斑海蛇(Laticauda laticaudata)的久高島和黑、黃唇青斑海蛇(L. colubrina)彼此共域的石垣島的海蛇為對象，觀察不同族群的黑唇青斑海蛇活動高峰與食物組成，以了解與競爭者共域是否會使其利用的資源有所區隔。調查時間在2012年的春、夏、秋3季進行，平均每季調查時間約23天，調查期間同時做行為觀察和捕捉，並以催吐方式獲得胃內含物，依地點不同，每次活動觀察歷時連續6-8小時，天數4-5天，捕捉方面則視季節和天氣而定。 活動季節方面，春季為黃唇青斑海蛇的活動高峰，而夏季至秋季期間可見活動個體數則降低，秋季為三季中最不活耀的季節，而在久高島的黑唇青斑海蛇在春季就開始出沒，夏季也可見其蹤跡，秋天才是活動的高峰；石垣島的黑唇青斑海蛇在春季可見量極少，夏季時最多，秋季又開始減少，此活動高峰季節的差異可能與棲地的利用或競爭有關。在單日活動高峰上，黃唇青斑海蛇在三個季節中的活動高峰都是19:00~20:00之間，而黑唇青斑海蛇的單日活動高峰在不同季節間有顯著差異，但是在兩個地點間則沒有差異，春季大約是19:00~20:00為活動高峰，夏季的活動高峰則延遲到22:00，秋季則是19:00過後整夜至0:00都有活動，顯示黑唇青斑海蛇的單日活動不受到競爭者的存在與否而改變，此行為模式可能為生理限制所調控。在食性方面，黃唇青斑海蛇的胃內含物中有大量的裸胸鯙及少量的康吉鰻，而兩地間的黑唇青斑海蛇皆以裸胸鯙為主食，但久高島的族群同時取食少量的非鰻型目的鰻鯰及魚卵，而石垣島的族群則會取食細長的蛇鰻，兩地利用的資源並非為黃唇青斑海蛇所用，顯示食性和競爭並無直接關係，而頭部形質也支持兩地間的食物有分化的可能，石垣島的黑唇青斑海蛇的頭寬比例較久高島的海蛇來的小，因此更適合吃體型較小的蛇鰻。 總結來說，在無競爭者的久高島，黑唇青斑海蛇的活動季節較延長，食物以裸胸鯙為主並伴隨著其他非鰻型目的魚類；在有競爭者共域的石垣島，黑唇青斑海蛇的活動季節集中於夏季，食物同樣以裸胸鯙為主，但會取食蛇鰻。然而，兩地海蛇的單日活動時間則無顯著差異，顯示其主要受到生理的調控。

Laticauda (Reptilia, Eplapidae) is a group of sea kraits that has to lay eggs, molt or digest food on the land. This research focuses on the feeding activities and diet compositions of L. laticaudata and L. colubrina in Kudakajima(with only L. laticaudata exist) and Ishgakijima(with both L. laticaudata and L. colubrina sympatry), Okinawa, Japan. The aim was to investigate possible diversifications of daily and seasonal activity patterns as well as diet compositions of sympatric populations comparing with those of allopatric populations. This study was conducted in Spring, Summer and Autumn in 2012, and the survey time in each season was about 23 days. In each survey, the occurrences of sea kraits at each site was recorded for 6 to 8 hours and lasted for 4 or 5 days. Sea kraits were caught to study their stomach contents. Seasonal activity pattern of L. colubrina peaked in spring and declined in summer and autumn, but for L. laticaudata, two populations show difference in seasonal activity patterns. Population of L. laticaudata in Kudakajima started to appear in spring, remained active in summer and peaked in autumn. While in Ishigakijima, L. laticaudata was rarely found in spring but peaked in summer and declined in autumn. This shorter activity season in Ishigakijima population may be due to the separation of habitat uses related to sympatric competition. Furthermore, daily activities of L. colubrina peaked around 19:00~20:00 in 3 seasons, while in L. laticaudata daily activities differed among seasons but there was no difference between populations. In spring, L. laticaudata at both sites had their activities peaked around 19:00~20:00. In summer, the peak of activities occurred at 22:00. In autumn, they were active throughout the night after 19:00. The fixed daily activity patterns may be due to physiology constraint to avoid overheat or water loss. Most of the stomach contents from L. colubrina were Gymnothorax with a small portion of Conger. In L. laticaudata, more than half of the stomach contents of L. laticaudata in both populations were Gymnothorax. But the population in Kudakajima ingested other fishes such as Plotosus lineatus and fish eggs, while the populations in Ishigakijima ingested Ophichthidae. The relative head width showed the possibility of diet divergence. Head width of Ishigakijima population was smaller than that of Kudakajima population, this may enable them to consume smaller food items such as Ophichthidae.