台北市公園鳥類群聚變遷：2003-2017年

Abstract

隨著都市擴張，自然棲地流失且破碎化，當地物種由少數偏好都市環境的外來種佔優勢而逐漸取代，造成群聚間的生物均質化（biotic homogenization），引起對都市生物多樣性的關注。過去都市鳥類研究著重探討空間尺度上的群聚變化，在時間尺度上群聚如何變動的研究則相對缺乏，因此本研究利用2003至2017年台北市16座公園的鳥類調查資料，首先以相似度指標檢視外來物種是否造成群聚間的均質化，接著將鳥類分別以遷徙屬性、食性、覓食棲地、築巢棲地及棲地廣適度進行同功群分析，並計算各同功群在16個樣區中物種數、豐度及相對豐度的平均變化趨勢，藉以探討十五年間台北都市公園鳥類的群聚變遷。 結果顯示整體鳥類物種數、豐度均呈上升趨勢。若排除外來物種，群聚間的相似度逐年下降；若納入外來種則無顯著變化，顯示外來種造成某程度上的生物均質化。大部分同功群的物種數及豐度均上升，然而各同功群的變化速度不一。外來種、雜食者、水域穀食者、蟲果穀食者、水域覓食者及森林棲地廣適者在三種指標均呈上升趨勢。其中，雜食者的增加速度高於其他食性同功群，推測能夠使用多樣人類產生的食物來源使雜食者在都市區域有足夠資源增加族群量。與水環境相關的同功群，如水域穀食及水域覓食者，顯示台北市公園提供合適的水域環境；而雖然森林廣適者在三種指標均上升，森林棲地專一者在物種數及豐度同樣上升且增加速度較快，雖過去認為都市化不利於棲地專一型物種，此研究推測適當的棲地營造可支持該類物種在都市區域生存；地面築巢者同樣被認為較無法適應都市環境，其物種數及豐度在十五年間也呈上升趨勢。此外，外來種及洞穴建物築巢者具有相似的變化趨勢，推測能使用建物孔洞進行築巢為外來種適應都市環境的重要原因之一。本研究藉由長期監測的資料，得知鳥類群聚的時空變遷，有助於評估台北市生物多樣性的狀況並做出合適的保育行動。

Urbanization results in loss of natural habitats and biodiversity. Bird assemblages are dominant by few species and share more similarity in highly urbanized regions, so called “biotic homogenization”, which raises concern of urban biodiversity. However, most of studies focused on spatial patterns. How assemblages changed over time is relatively unexplored. Hence, this study used monitoring data of 16 Taipei parks from 2003 to 2017 to investigate temporal changes of bird assemblages. We used similarity indices to examine the effects of exotic species on biotic homogenization. Then, we used five traits (residence status, diet, foraging site, nesting site and habitat) and three indices (richness, abundance, relative abundance) to determine if there were different temporal trends in guilds. The results demonstrated an upward trend in both overall species richness and total abundance. After excluding exotic species, similarity indices decreased through time, which implied that they to some degree drove the homogenization of assemblages. Guilds exhibited different trends. Exotic species, omnivores, insecti/frugi/granivores, aquatic/granivores, aquatic foragers and forest generalists significantly increased in all indices. Most of guilds had positive trends in richness and abundance, but rates of increase were divergent. Omnivores increased faster than other diet guilds, which may result from their ability to utilize a variety of food types, including human-provided food. Increase of water-associated species, such as aquatic/granivores and aquatic foragers, reflected a good aquatic environment in Taipei city. Forest generalists indicated positive trends in all indices; however, forest specialists showed a faster increase in richness and abundance. Though forest specialists used to be viewed as urban avoiders, this study deduced that supplements of suitable habitats can support their population in urban areas. The same situation was also found in ground nesters; however, there is still a lack of directly environmental evidence. In addition, exotic species and cavity/building nesters shared similar change patterns; thus, the ability to nest in man-made structures may be important for them to adapt well in urban environments. With the long-term monitoring data, the study provided the temporal perspective of bird assemblages, which can help to reach a more comprehensive and efficient actions of diversity conservation.