造橋地區赤尾青竹絲(Trimeresurus s. Stejnegeri)不同年齡群存活率之推估與探討
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Date
2006-06-??
Authors
林華慶
李丕強
杜銘章
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Journal ISSN
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Publisher
國立臺灣師範大學生命科學學系
Department of Life Science, NTNU
Department of Life Science, NTNU
Abstract
自1996-2005年期間，我們針對位於苗栗縣造橋鄉的一個赤尾青竹絲(Trimeresurus s. stejnegeri)野外族群，以重複捕捉的方法研究並推估族群以及群內不同年齡群體在研究期間的平均存活率。我們共計標放577隻赤尾青竹絲，其中幼蛇共有180隻，年輕成蛇共有236隻，年長成蛇則有161隻；所有的重複捕捉資料共計2095隻次。我們所推估的族群平均存活率為0.72，平均捕取率為0.59。尚未達性成熟的幼蛇其平均存活率為0.62，捕取率為0.41；達到性成熟後的年輕成蛇其平均存活率為0.73，捕取率為0.65；年長成蛇的平均存活率與摘取率則分別為0.72與0.62。不同年齡群體之間，幼蛇的存活率與捕取率均顯著低於年輕成蛇；同時也低於年長成蛇。而年輕成蛇與年長成蛇之間的存活率與捕取率則均無顯著差異。幼蛇的較低存活率可能與牠們較容易被天敵捕食，或是較無法耐受食物短缺所致。赤尾青竹絲在幼蛇時期的存活率較低，而達到性成熟後的群體則保有高而穩定的存活率，此特徵符合典型的脊椎動物第二型存活率曲線模式。而赤尾青竹絲的存活率比已研究的大部分黃頷蛇類高，並與許多壽命達10年以上的蝮蛇類相近，此一較高的存活率可能是因為其屬於定點伏擊的掠食者，行蹤被天敵發現的機率較低；以及其綠色體色在樹棲生活中具有較佳的保護效果，能有效降低被天敵捕食的風險。
To estimate the population survivorship in the Chinese green tree viper (Trimeresurus s. stejnegeri), a mark-recapture study was conducted from 1996 to 2005 at Tsao-chiao, northern Taiwan. Over the course of nine years, a total of 577 individuals were captured. The maximum likelihood averaged estimates of half-year survival and capture probability was 0.72 and 0.65 respectively. In different age classes, averaged survival and catch probability estimates were 0.62 and 0.41 for immatures, 0.73 and 0.65 for younger adults, and 0.72 and 0.62 for older adults, respectively. The averaged survival and catch probability estimates for immatures were significantly lower than those for young adults and old adults. However, no significant difference in the estimated survival rates or probabilities was found between young adults and old adults. The lower survivorship of immatures might result from the fact that hatchlings and juveniles are more vulnerable to predators and starvations than adults. Survivorship curve for Trimeresurus s. stejnegeri appears to conform to the type II pattern, showing age-constant higher survival after maturity. The higher survival of Trimeresurus s. stejnegeri might result from their sit-and-wait foraging strategy since ambush foragers are less exposed to predators than active foragers. Additionally, green cryptic coloration of Trimeresurus s. stejnegeri are likely to minimize the risks of being attacked by potential predators.
To estimate the population survivorship in the Chinese green tree viper (Trimeresurus s. stejnegeri), a mark-recapture study was conducted from 1996 to 2005 at Tsao-chiao, northern Taiwan. Over the course of nine years, a total of 577 individuals were captured. The maximum likelihood averaged estimates of half-year survival and capture probability was 0.72 and 0.65 respectively. In different age classes, averaged survival and catch probability estimates were 0.62 and 0.41 for immatures, 0.73 and 0.65 for younger adults, and 0.72 and 0.62 for older adults, respectively. The averaged survival and catch probability estimates for immatures were significantly lower than those for young adults and old adults. However, no significant difference in the estimated survival rates or probabilities was found between young adults and old adults. The lower survivorship of immatures might result from the fact that hatchlings and juveniles are more vulnerable to predators and starvations than adults. Survivorship curve for Trimeresurus s. stejnegeri appears to conform to the type II pattern, showing age-constant higher survival after maturity. The higher survival of Trimeresurus s. stejnegeri might result from their sit-and-wait foraging strategy since ambush foragers are less exposed to predators than active foragers. Additionally, green cryptic coloration of Trimeresurus s. stejnegeri are likely to minimize the risks of being attacked by potential predators.