Demography of Two Small Breeding Populations of Taipei Grass Frog, Rana Taipehensis van Denburgh (Amphibia, Anura)

Abstract

從2003至2004年，我們調查了二個臺北赤蛙(Rana taipehensis)的繁殖族群，分別位於三芝及楊梅。繁殖族群的性別比明顯的偏向雄性，三芝族群的雄雌性別比(16.13:1)約是楊梅族群的二倍(6.97:1)。以Schnabel 法估算的二個族群數量，在2004年皆呈下降的現象。骨骼鑑齡上定義每一生長停滯線(LAG)代表一歳，族群 中年紀最大的個體在雌性及雄性皆為4歳，雌蛙的年齡(2.56±0.09 LAGs)顯著的大於雄蛙(2.30±0.03 LAGs)。依據年齡結構的分析結果，一些雄性個體在1歳時就能達到性成熟且進入到繁殖族群內，雌蛙則要到2歳。楊梅族群中雌蛙在2歳至3歳的存活率最高(0.68)，但是此階段在三芝族群有最低的存活率(0.22)。從雌蛙的存活率，我們認為棲地干擾（三芝）對雌蛙有負面效應。性別比可能會受到人為擾動的間接影響。

In 2003 and 2004, we surveyed different populations of Taipei grass frog (Rana taipehensis) living at Sanchih and Yangmei, Taiwan, using waist-band and toe-clipping methods. Sex ratios of breeding populations of this frog were skewed to males. The ratio of male to female frogs from Sanchih population (16.13:1) was almost twice that from Yangmei (6.97:1). Estimated population sizes, using the Schnabel method, were declining in 2004 both at Sanchih and Yangmei. We defined one line of arrested growth (LAG) as one year old. The oldest frog was 4 years old according to skeletochronology of both males and females. The age of females (2.56±0.09 LAGs) was significantly older than that of males (2.30± 0.03 LAGs). Based on age structure, some males reached sexual maturity and joined the breeding population in 1 year. For females it was in 2 years. From age 2 to 3, females living at Yangmei had the highest survival rate (0.68), but at Sanchih had the lowest survival rate (0.22). From the survival rates of females, we supposed that disturbed habitats (at Sanchih) may have a negative effect on females. The sex ratio may be affected by human disturbance indirectly.