遊蕩犬對臺灣原生食肉動物時空生態棲位之影響

Abstract

群聚中的物種能透過調整現實生態棲位以降低種間競爭。然而，當面臨強大的共同掠食者時，物種可能會增加與掠食者的生態棲位分化，以迴避威脅。這可能導致物種間的生態棲位重疊度增加，進而可能降低物種的適存度（fitness）。家犬（Canis familiaris）是世界上分布最廣泛的入侵食肉動物，對原生食肉動物造成嚴重威脅，本研究假設犬隻造成的掠食壓力會導致：（1）原生食肉動物與遊蕩犬的活躍程度（relative activity index, RAI）呈負相關；（2）原生食肉動物與遊蕩犬的生態棲位時空分化增加；（3）原生食肉動物之間的生態棲位時空分化降低。本研究以臺灣中低海拔的四種中型食肉動物為研究對象，包含白鼻心（Paguma larvata）、鼬獾（Melogale moschata）、麝香貓（Viverricula indica）與食蟹獴（Herpestes urva）。我們共蒐集到1270台自動相機之資料，計算各物種RAI、建立佔據模型（occupancy modeling）與核密度估計（kernel density estimation），分析物種空間利用及活動模式重疊度的變化。研究發現，遊蕩犬與鼬獾RAI（P < 0.001）與食蟹獴RAI（P < 0.05）呈顯著負相關，顯示犬隻對其族群可能有負面影響。而鼬獾在佔據度上表現出迴避犬隻的現象（Species Interaction Factor, SIF < 1），代表其與遊蕩犬具有空間生態棲位的分化。然而，物種的活動模式重疊度未受任何因子影響。此外，我們也沒有發現原生食肉動物之間的生態棲位時空分化受遊蕩犬影響，我們推測可能有三種原因：（1）研究對象中僅有鼬獾在棲地利用上表現出對遊蕩犬迴避的傾向，其餘物種則無，故原生物種間的現實生態棲位並沒有重疊度增加的現象。（2）原生食肉動物的時空生態棲位具有更細微的分化，本研究中難以偵測。（3）有重要的因子影響原生食肉動物的時空生態棲位，導致狗對各個物種分別的影響沒有改變原生食肉動物的現實生態棲位並增加重疊度。例如即便食蟹獴與犬隻RAI顯著負相關，我們卻沒有觀察到食蟹獴迴避犬隻的現象（SIF > 1），這可能與其高度依賴特定環境生存有關，使其未能靈活改變棲地。本研究證實了遊蕩犬對鼬獾與食蟹獴造成衝擊，後續研究應進一步整合生態棲位的其他維度，更能清楚了解犬隻對原生食肉動物群聚造成的影響。

Species within a guild can reduce interspecific competition by partitioning their realized niches. However, when facing co-predators, species may partition their niche with their co-predators to avoid threats. However, this reduction in niche overlap with predators may lead to an increase in the niche overlap among prey species, thereby potentially reducing the prey species’ fitness. Dog (Canis familiaris) is the most common invasive carnivore worldwide, posing severe threats to native carnivores. In this study, we hypothesize that the predation by free-ranging dogs will result in (1) a negative correlation between the relative activity index (RAI) of native carnivores and dogs, (2) increased spatiotemporal niche partitioning between native carnivores and dogs, and (3) decreased spatiotemporal niche partitioning among native carnivores. This study focused on four meso-carnivores in Taiwan, including the masked palm civet (Paguma larvata), ferret-badger (Melogale moschata), small Indian civet (Viverricula indica), and crab-eating mongoose (Herpestes urva). Data from 1270 camera traps were analyzed using occupancy modeling and kernel density estimation to assess species' spatial and temporal niche overlap changes. Results revealed a significant negative correlation between the RAI of dogs and ferret-badgers (P < 0.001), as well as dogs and crab-eating mongooses (P < 0.05). The ferret badger exhibited a significant spatial avoidance of dogs (Species Interaction Factor, SIF < 1), indicating spatial niche partitioning with dogs. However, the overlaps of species’ activity patterns were not influenced by any factor. Also, we did not observe any influence of free-ranging dogs on the spatiotemporal niche partitioning among native carnivores. There were three potential explanations: (1) Only the ferret badger showed spatial avoidance of dogs, while other species did not. Thus, no increase in niche overlap was observed. (2) More subtle partitioning on the spatiotemporal niches of native carnivores might exist, but it was difficult to detect in this study. (3) There were more vital factors influencing the spatiotemporal niches of native carnivores, so the threats posed by dogs on individual species were not able to alter their realized niches nor increase their niche overlap. For instance, despite the significant negative correlation between the RAI of crab-eating mongooses and dogs, we did not observe avoidance behavior in crab-eating mongooses (SIF > 1). This situation was likely due to their high dependency on specific environments for survival, which limited their ability to alter their habitats flexibly. In conclusion, this study confirms the negative impacts of free-ranging dogs on the ferret badger and mongoose, suggesting further research to integrate other niche dimensions for a comprehensive understanding of the effects of dogs on the niche partitioning of native carnivores.