以模式及生長發育數據解釋物種分布在臺灣的情形-以翠斑青鳳蝶為例

Abstract

生物的分布及豐量變化常與氣候變化有關聯。族群的向極地遷移(poleward shift)多被認為可能與氣候暖化有關，但族群的分布變化不單是受氣候影響，與其他物種的交互作用也不可忽視，且多項研究僅以模式(modeling)分析模擬物種分布與氣候的關係，少有研究加入生理實驗佐證其結果。近年來臺灣的年均溫上升趨勢明顯，原來分布在南部的熱帶蝶種翠斑青鳳蝶(Graphium agammemnon agammemnon)近年也有族群擴散至中北部的趨勢，但尚未在北部有穩定族群的建立，由於其寄主植物為泛全島性分布，顯見食物來源本身非共分布限制因素。為了探討翠斑青鳳蝶在臺灣分布情況的成因，本研究先進行為期一年的寄主植物(烏心石)物候，確認翠斑青鳳蝶幼蟲食草的取得全年於北、中、南各樣區均無虞，因此可以排除寄主植物物候是造成翠斑青鳳蝶族群範圍受限的因素，溫度對翠斑青鳳蝶幼生期發育影響的生理實驗結果則顯示翠斑青鳳蝶幼蟲的發育速率隨著溫度升高有逐漸增加的趨勢(幼生期的溫度與發育速率回歸方程式為y= 0.0036x - 0.0344, y=發育速率, x=溫度)，利用有效積溫研究推算出的發育起點溫度為9.22℃，並由不適低溫探測的結果得知4℃~12℃約為翠斑青鳳蝶幼生期的不適存低溫範圍，而4℃可能為翠斑青鳳蝶幼生期的致死低溫，並以模式分析翠斑青鳳蝶幼生期的分布狀況，在臺灣主要是受到最冷月最低溫(模式貢獻百分比為49.4；AUC=0.805)的影響，且各地的幼蟲分布機率隨著溫度的上升而增高，實際比對中央氣象局在2015年各測站的最冷月最低溫資料，依據文獻與本研究觀察結果發現，溫度在翠斑青鳳蝶幼蟲不適溫度範圍內的地區，至少在當季(冬季)不易記錄到幼蟲個體。本研究驗證了翠斑青鳳蝶的發育會受溫度影響，且不適低溫可能是影響穩定族群建立的關鍵因子。It is well known that climate change may affect species’ distribution and abundance. For instance, poleward shift of organisms is often thought to be related to climate warming. However, the change of population distribution is affected not only by climate change, but also the interaction with other species. Most of the researches that deal with the relationship between species distribution and climate are detected by modeling. Few of them employ physiological data to strengthen the result. Recently, mean temperature in Taiwan has risen considerably. A tropical butterfly species Graphium agamemnon agamemnon that used to confine to southern Taiwan has been found in central and northern Taiwan. Stable population of this butterfly is now well established in central Taiwan, but not yet so in the north, even though its host plants are widely distributed all over Taiwan. In order to know what has caused the change of distribution of Graphium agamemnon agamemnon in Taiwan, the phenology of host plants was first investigated, and it was found that fresh tissues are available all over Taiwan through whole year. Consequently, phenology of the host plants may not limit distribution of the butterfly. A gradient thermal experiment was then performed to see how temperature affected their development. Information with modeling was added to simulate the population distribution by past data. The result reveals the developmental rate increased with the increase of temperature (y=0.0036x-0.0344; y=developmental rate, x=temperature). The developmental threshold of the immature stage was 9.22℃. The lower lethal threshold may be 4℃, and the lowest optimal threshold may be 12℃. By modeling, it determined that the distribution of Graphium agamemnon agamemnon was mainly caused by minimum temperature of coldest month (percent contribution:49.4; AUC=0.805). The increase of temperature shows higher probability of larvae’s occurrence. It was found that areas suffering temperatures lower than the lowest optimal threshold were less likely to find larva in the winter. The present study demonstrates that the development of Graphium agamemnon agamemnon is affected by temperature, and low temperature may strongly limit stable population’s distribution.