台灣三種鈍頭蛇的獵物選擇、攝食表現與生態棲位模擬

Prey choice, feeding performance and ecological niche modeling of Pareas species in Taiwan

張凱翔(Chang Kai-Xiang)

指導教授 ： 林思民

國立臺灣師範大學/理學院/生命科學系/碩士(2019年)

https://doi.org/10.6345/NTNU201900800

摘要

鈍頭蛇科的成員是蝸牛及蛞蝓的專食者，下頷齒數左右不對稱，右側牙齒普遍比左側多。先前研究推測下頷的不對稱性可能是鈍頭蛇由於專食右旋蝸牛所產生的演化適應，然而牙齒不對稱的程度在鈍頭蛇物種間具有頗大的變異性，我推測這樣的差異可能反映其食性偏好及攝食表現。在台灣三種鈍頭蛇當中，泰雅鈍頭蛇（P. atayal）的牙齒不對稱指數（asymmetry index）最高、台灣鈍頭蛇（P. formosensis）最低，駒井氏鈍頭蛇（P. komaii）則介於兩者之間，因此適於檢驗上述假說。行為實驗的結果顯示，台灣鈍頭蛇只吃蛞蝓、不吃蝸牛，泰雅鈍頭蛇及駒井氏鈍頭蛇大部分的個體則是兩者皆會取食，但沒有只吃蝸牛的個體。在攝食表現方面，泰雅鈍頭蛇傾向從左後方攻擊蝸牛，且吞食蝸牛的效率高於駒井氏鈍頭蛇。廣義線性混合模型（GLMMs）分析指出兩種鈍頭蛇攻擊蝸牛的成功率以及吞食蛞蝓的時間、下頷骨運動次數均沒有顯著差異；鈍頭蛇攻擊蝸牛成功與否受到蝸牛重量影響，吞食蛞蝓的效率受到蛞蝓重量影響，吞食蝸牛的效率受到鈍頭蛇物種的影響。為了檢測獵物資源是否會影響鈍頭蛇在野外的分布，我透過物種分布預測軟體（Maxent）進行生態棲位模擬（ecological niche modeling）。結果指出，對於泰雅鈍頭蛇、駒井氏鈍頭蛇及台灣鈍頭蛇的分布貢獻度最大的因子分別為蝸牛的分布、降雨的季節性以及蛞蝓的分布。綜合行為實驗及棲位模擬的結果，本研究顯示台灣的三種鈍頭蛇在攝食行為與生態棲位上皆展現了一定程度的分化。鈍頭蛇牙齒的不對稱性與其獵物偏好、攝食表現相關，且鈍頭蛇在野外的分布也受到獵物資源的影響。牙齒最不對稱的泰雅鈍頭蛇在攝食表現上展現了對蝸牛的適應，在野外分布受到蝸牛的影響；牙齒不對稱性最低的台灣鈍頭蛇在食性偏好上展現了對蛞蝓的適應，在野外的分布受到蛞蝓的影響。

關鍵字

不對稱指數 ； 食性偏好 ； 食蝸蛇 ； 腹足類 ； 攝食效率

並列摘要

Specialized in feeding land snails and slugs, the members of Pareidae (Squamata: Serpentes) have asymmetric jaws, with their teeth on the right side more than those on the left side. Previous studies have found that predation success of Pareas on sinistral snails is lower than that on dextral snails, which suggest that the evolution of asymmetric dentition in Pareidae might be an adaptation to specialized food habits of dextral snails. However, the level of teeth asymmetry in Pareidae varies among species, which may reflect their prey preferences and feeding performances. Pareas species in Taiwan (P. atayal, P. komaii, and P. formosensis) have different levels of teeth asymmetry, which make them suitable for testing this hypothesis. Behavioral experiments showed that P. formosensis fed exclusively on slugs, while none of P. atayal and P. komaii fed exclusively on snails; most individuals of P. atayal and P. komaii fed both slugs and snails. In terms of feeding performance, P. atayal tended to strike a snail from its posterior-left direction and exhibited higher efficiency (shorter handling time and fewer mandibular movements) to prey on snails than P. komaii. GLMMs showed that P. atayal and P. komaii did not differ in the handling time and number of mandibular movements on slugs, as well as in the predation success on snails. Prey weight had effect on the predation success on snails and on the feeding efficiency upon slugs. Snake specie, instead of prey weight, affect the feeding efficiency on snails. To examine the effects of prey resources on the distribution of Pareas species in the wild, I used Maxent to model the ecological niche of the three snake species. The results showed that the distribution of flat-shelled Satsuma snails, the distribution of Montane Slug (Meghimatium fruhstorferi), and precipitation seasonality are the most important factors that influence the distribution of P. atayal, P. formosensis, and P. komaii, respectively. This study reveals that dentition asymmetry is associated with prey preference and feeding performance: P. atayal, with the most asymmetric teeth, shows adaptation to snails in terms of feeding performance, while P. formosensis, with the most symmetric teeth, shows adaptation to slugs in terms of prey preference. Additionally, the ENM results indicate that the distributions of Pareas species are relevant to the prey resources. Combining the results of behavioral experiments and ENM, it is suggested that three Pareas species in Taiwan exhibit differentiation in feeding behaviors and ecological niches.

並列關鍵字

asymmetry index ； feeding efficiency ； Pareidae ； prey preference

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