合歡山地區台灣高山田鼠啃食作用對玉山箭竹生長之影響

Abstract

草食動物雖常被認為對植物的更新、生長、存活有負向的影響，但可能也有正向的影響。草食動物在攝取植物不同部位時，會對植物的適存度有不同影響。在合歡山草原地區，主要的優勢植種為玉山箭竹(Yushania niitakayamensis)，主要的優勢小型哺乳動物為台灣高山田鼠(Microtus kikuchii)， 過去的研究顯示玉山箭竹為高山田鼠主要偏好的植種。本研究希望了解高山田鼠與玉山箭竹之間的關係，因此進行檢驗了以下的假說：(1)台灣高山田鼠對於玉山箭竹的不同部位有取食偏好差異；(2)取食偏好與不同部位的營養成份相關，高偏好的部位含有較高的蛋白質及較低的纖維；(3)台灣高山田鼠對玉山箭竹的取食會增加箭竹冠層光的穿透量及地面掉落物，進而對玉山箭竹的生長有正向的影響。本研究分為實驗室內的取食偏好實驗和箭竹營養成分分析實驗，以及使用野外圍欄移除田鼠實驗和操弄覆蓋度、掉落物實驗兩大部分。實驗結果顯示，高山田鼠對於玉山箭竹各部位有顯著的取食偏好差異，且具有季節上的差異，五月時的取食偏好等級為筍＞葉＞地下莖=地上莖，在一月及十月時的取食偏好等級為葉＞筍=地下莖=地上莖。高山田鼠對各部位的取食偏好與箭竹的酸洗纖維、粗蛋白質及灰份等營養成分含量顯著相關。高山田鼠的啃食活動會降低箭竹覆蓋度及增加掉落物，進行野外降低箭竹覆蓋度及移除掉落物的實驗顯示兩者對箭竹發筍均有顯著的影響。而圍欄實驗的結果亦顯示，移除田鼠會降低圍欄內箭竹筍與莖的比例。因此可得知台灣高山田鼠雖然取食玉山箭竹，但對箭竹的生長具有正向的影響。

Although herbivores are often considered having negatively influence on the recruitment, growth, and survival rate of plants, they could benefit plants as well. The herbivorous consumption of different plant parts could have differential effect on fitness of the consumed plants. Yushan canes (Yushania niitakayamensis) is the dominant plant species, and Taiwan vole (Microtus kikuchii) is the dominant small mammal in alpine meadows at the Hehuan Mt.. The former species is the primary and preferred food of the latter species. In this thesis, investigation was set up to elucidate the relationship between the two species. Hypothesis of the study are (1) Taiwan voles have feeding preference on different parts of Yushan canes; (2) feeding preference can be explained by nutrient contents of different parts: highly preferred parts have higher protein and lower fiber contents than less preferred parts; (3) consumption by Taiwan voles has positive effects on the growth of Yushan canes by increasing light penetration into the canopy and aboveground litter. Feeding preference experiments and nutrient content analyses were performed in the laboratory, and field exclosures and field manipulation of canopy and litter were used to test the hypotheses. The results indicated that the ranks of feeding preference by Taiwan voles were shoot > leaf > culm = rhizome in May, and leaf > shoot = culm = rhizome in January and October. The preference was explained by nutrient contents, particularly the amounts of acid detergent fiber (ADF), crude protein (CP), and ash of Yushan cane parts. The exclusion of voles led to decreased shoot-culm ratios. Both the reduction of canopy cover and litter removal had significant effects on the emergence of new shoots after 1 year of field manipulation, indicating that Taiwan voles could facilitate shoot emergence of Yushan canes through increasing light availability and ground litter. I conclude that although Taiwan voles consume Yushan canes, they could benefit Yushan canes as well.