- 學位論文
人類活動對臺灣地區石虎食性之影響
Anthropogenic influences on the diets of the leopard cat Prionailurus bengalensis in Taiwan
摘要
面對全球頂級掠食者（apex predators）族群持續下降的趨勢，中階掠食者（mesocarnivores）所能扮演的生態功能日益受到關注。石虎（Prionailurus bengalensis）作為臺灣淺山生態系中少數以脊椎動物為主食的中階掠食者，其覓食行為不僅影響自身的生存，也可能透過複雜的食物網進而影響許多其他物種以及生態系過程。因為棲地喪失、破碎化和獵捕，臺灣的石虎分佈已大規模限縮至中部地區，根據臺灣野生動物保育法被列為瀕臨絕種之保育類野生動物，若其族群能恢復並擴張分佈至更多淺山地區，牠們可能發揮重要的掠食者生態功能。本研究結合排遺內含物形態分析和碳氮穩定同位素分析（排遺樣本67個、毛髮樣本46個），並且利用貝氏混合模型以掠食者和獵物在碳氮空間上的距離估算各食物來源的貢獻度，以了解臺灣地區石虎食性組成及其如何受人類活動的影響而變化。結果顯示，石虎食性頗寬，反應其機會主義式的覓食行為或食物資源的不穩定性。排遺形態分析顯示，在五大類獵物類群中（哺乳類、鳥類、爬蟲類、節肢動物、魚類），84% 的樣本含有至少兩大類之獵物。排遺與毛髮同位素分析則顯示，兩棲爬蟲類與節肢動物、哺乳類與鳥類此兩類獵物群對石虎食性的貢獻度相似，構成其主要食性，然根據毛髮同位素值，人類食物對石虎食性亦有約 30.2% 的貢獻度。與過去以排遺形態分析為主的研究結果相似，本研究排遺形態分析亦顯示哺乳類動物，特別是鼠科動物，是石虎重要的獵物之一，然綜合同位素分析結果可知，節肢動物和爬蟲類亦為石虎重要的獵物，這是單用排遺形態分析容易忽略的訊息。整體來說，石虎佔據當地食物網較高的營養位階，接近人類（當地居民）的營養位階。隨著人類活動（以農地覆蓋度表示）的增加，石虎排遺中出現人造物的機率升高，排遺和毛髮的碳氮同位素值也有上升趨勢，顯示石虎可能有取食人類食物的現象。排遺形態分析和排遺同位素分析所得的食性資訊存在一定差異，兩種方法的結果併同使用可更完整地呈現野生動物的食性。本研究揭示了人類活動對臺灣石虎食性的影響，而這些改變是否對石虎的生存和族群健康有影響，則有待進一步探討。
並列摘要
The global decline of apex predators has led to a growing interest in the ecological functions of mesocarnivores as a way to compensate for the loss of apex predators. In the suburban hills of Taiwan, the leopard cat (Prionailurus bengalensis) is an important mesocarnivore that primarily feed on vertebrates, whose foraging behavior not only influences its own survival, but can also affect many other species and ecosystem processes complex food-web interactions. Due to habitat loss, fragmentation, and hunting, the geographic distribution of leopard cats in Taiwan has been largely restricted to the central region. As a result, the leopard cat is currently listed as ‘endangered’ according to Taiwan’s Wildlife Conservation Act. If their populations recover and expand into more low-altitude areas, leopard cats could potentially fulfill important ecological roles as predators. This study combined scat content morphological analysis and stable isotope analysis of carbon and nitrogen (using 67 scat samples and 46 fur samples). A Bayesian mixing model was used to estimate the contribution of each food source based on the distance between predators and prey on carbon-nitrogen isospace. These approaches aimed to understand the dietary composition of leopard cats in Taiwan and how it is influenced by human activities. The results showed that leopard cats have a rather broad diet with considerable variation in prey composition, reflecting opportunistic foraging behavior or instability in their food resources. Morphological scat analysis showed that 84% of samples included prey from at least two of the five major prey groups (mammals, birds, reptiles, arthropods, and fish). Both scat and hair isotope analyses indicated that reptiles and arthropods, as well as mammals and birds, contribute similarly to their diet, together forming their main dietary components. Interestingly, based on hair isotope values, human-derived food sources also contributed approximately 30.2% to their diet. Similar to previous studies based mostly on morphological scat analysis, we confirmed that mammals, especially rodents, are key prey for leopard cats. However, integrating the results of isotope analysis, we also uncovered the importance of arthropods and reptiles, which would have been easy to miss if we relied on scat morphology alone. Overall, leopard cats occupy a relatively high trophic position in the local food web, comparable to that of local human residents. With increased human activity (measured by the proportion of cultivated and managed vegetation area), the frequency of occurrence of artificial items in scats increased , and the carbon and nitrogen isotope values of both scat and hair showed an increasing trend. These findings suggest that leopard cats may be incorporating human-related food sources into their diet. While analyses of scat morphology and isotope composition each provide dietary insights, the differences between them highlight the value of using both methods to gain a more comprehensive understanding of wildlife feeding habits. This study reveals the influence of human activities on the diet of leopard cats in Taiwan, yet further research is needed to determine whether these dietary changes impact their long-term survival and population health.