台灣中西部地區蚯蚓之特有性及其垂直分布

Endemicity and Altitudinal Stratification in Distribution of Megascolecid Earthworms in the Centro-western Taiwan

Earthworm surveys were conducted in the centro-western Taiwan from the coastal plain at 50m in elevation near the Tatu Estuary to Mt. Hohuan at 3,200m in the Central Mountain Range in 1999, 2000 and 2003. A total of 34 species of megascolecid earthworms were collected, consisting of 19 native species and 15 exotic species. Most of the native species were woodland earthworms, dwelling primarily in the mountain range and its peripheral hills. They showed altitudinal stratification in the distribution; each species had its specific geographical area with the highest and the lowest altitudinal ranges. Apparently, elevation defines the distributional ranges, and is one of the important factors for autochthonous speciation of the native species. In contrast most of the exotic species were farmland earthworms commonly found in the coastal plain and at the foot of peripheral hills, and showed the altitudinal stratification only in the highest altitudinal ranges. Apparently, their species-specific adaptability to climatic and environmental conditions in the hill and mountain regions defines the highest altitudinal ranges of their distribution. With the decrease in elevation, number of native species decreased while number of exotic species increased, suggesting the presence of species shift from native forms to exotic forms in the earthworm communities, and the shift was higher at low elevations than at high elevations. 自1999年至2000年於中央山脈西側集集至合歡山區以及2003年於集集至大肚溪口共採得34種蚯蚓，其中特有種19種，外來種15種。特有種在海拔高度上有其特定之分布上下限，形成不同物種垂直分層的現象；外來種則自平地至山區皆有分布，僅分布上限因物種而有所不同。高海拔處之特有性較低海拔處為高。海拔高度下降，則蚯蚓特有種種數隨之減少，而外來種種數隨之增加，顯見物種組成有自特有種轉換成外來種之趨勢，此趨勢又以低海拔處較高海拔處明顯。