與蝶同行？城市人行道作為紋白蝶屬蝴蝶棲地之評估

Abstract

現今都市佔地快速增加，評估其作為生物棲地的可能性漸趨重要。以往研究多關注公園等人為模擬自然之區域，較少探討更典型的都市環境（如人行道）。因此本研究想知道都市廣布的人行道（如臺北市人行道約940公里，佔近1%土地面積）所提供的生態棲地價值。我們探討：(1)人行道是否能作為野生生物（如紋白蝶屬蝴蝶）的合適棲地？(2)人行道上的生物與非生物環境如何影響野生生物的表現？我們的研究包含以下五個實驗： (1) 為了解食草資源分布，每月調查人行道上可供紋白蝶幼蟲利用的食草量。 (2) 為比較紋白蝶利用人行道與自然棲地的情況，在蝶季中每日調查樣區食草上的卵與幼蟲族群量。 (3) 為瞭解人行道及自然棲地中非生物環境因素（如溫度）對紋白蝶幼蟲的影響，分別在人行道與自然棲地中飼養臺灣紋白蝶幼蟲，量測其存活率及發育速度。 (4) 為進一步了解人行道環境溫度（平均高溫及溫度起伏）對紋白蝶的影響，本研究利用實驗室生長箱模擬人行道與自然棲地環境（溫度設定分別模擬人行道日夜溫度變化、人行道固定日夜均溫、野外日夜溫度變化），並於各模擬環境下飼養臺灣紋白蝶幼蟲，量測其存活率及發育速度。 (5) 為比較人行道與自然棲地的生物因素（如捕食率與人類活動）對紋白蝶存活率之影響，本研究在人行道與自然環境放置蝶卵及假幼蟲，觀察其受干擾情形。 此外，本研究亦利用實地觀測資料，建立使用氣象資料預測人行道溫度的方法，以及使用人行道上臺灣紋白蝶幼蟲體長來推估齡期之轉換方法。 2016至2018年之研究結果顯示，人行道上具有紋白蝶的食草資源（實驗1與2），且紋白蝶在生長季節時的確利用人行道作為棲地。非生物環境因素實驗顯示，相較於野外棲地，人行道上的紋白蝶幼蟲有類似甚至較高的存活率，以及較快的發育速度，暗示人行道可以是比野外環境更好的棲地（實驗3）。在實驗室生長箱的溫度模擬實驗亦顯示相同結果，佐證人行道的高溫環境可以加速紋白蝶幼蟲的生長（實驗4），並且此加速現象主要因為人行道較高的平均溫度，而非較大的溫度起伏。生物因素部分，相比野外棲地，人行道上的蝶卵受到的捕食壓力較小，然而幼蟲受到較多人類活動干擾（實驗5）。綜合以上研究結果，我們認為都市環境如人行道，是被低估但重要的野生動物棲地（例如紋白蝶），因此我們建議都市管理者進行生態調查，並以更好的管理方式增進都市的生態價值。

Global urbanization has rapidly increased urban areas. Studies have evaluated urban environment (e.g., parks) as habitat for wildlife; however, few studies have examined the role of urban sidewalks as wildlife habitat. Given that sidewalks are a common component of cities worldwide (e.g., about 900 km long or 1% area in Taipei city), this study investigated (a) whether sidewalks in an international city (e.g., Taipei) can be suitable habitat for wildlife (e.g., Pieris butterflies), and (b) how the abiotic and biotic factors on sidewalks affect wildlife performance. Our study included these five experiments (Exp.): (1) To evaluate the food resource on Taipei sidewalks, this study conducted monthly surveys on the host plants of Pieris in Taipei sidewalk vs. field habitats. (2) To examine whether Pieris butterflies inhabit sidewalks, this study conducted daily surveys on Pieris density on sidewalks during Pieris seasons. (3) To compare how the abiotic factors (mainly temperature) of sidewalks and field habitats affect Pieris performance, this study raised Pieris larvae on caged plants in both sidewalk and field habitats. (4) To further examine the effect of average temperature, temperature fluctuation, and other abiotic factors on Pieris larval performance, this study raised Pieris larvae in laboratory cage experiments, which simulated sidewalk and field habitat temperatures (i.e., sidewalk-fluctuating, sidewalk-fixed and field-fluctuating temperature regime). (5) To compare how the biotic factors (predation and human disturbance) of sidewalk and field habitats affect the survivorship of Pieris eggs and larvae, this study placed Pieris eggs and larval decoys in sidewalk and field habitats. Furthermore, this study created conversion criterion of larval body length into larval stage, and of weather temperatures into sidewalk temperatures. The results of year 2016 – 2018 showed that Pieris and host plants did inhabit sidewalks (Exp. 1 and 2). Pieris larvae had similar survivorship in sidewalk and field habitats. Pieris larvae developed faster in sidewalk than field habitats (Exp. 3). The results of survivorship and development rate suggest that sidewalk could be as good as or even better than field habitats in terms of Pieris larval performance. The faster development under sidewalk temperature regime was also confirmed in laboratory experiments (Exp. 4). Moreover, the accelerated development on sidewalks was mainly due to high average temperature instead of temperature fluctuation (Exp. 4). Finally, Pieris on sidewalks faced a lower predation pressure on eggs but higher human disturbance on larvae (decoys), compared to those in the field (Exp. 5). Taken together, our results suggest that urban sidewalks, while underappreciated, can serve as an important habitat for wildlife such as Pieris butterflies. Therefore, this study encourage city managers to investigate and improve the ecological value of urban areas.