氣候及生物因子對尼泊爾埋葬蟲與紅胸埋葬蟲海拔分布的影響

Abstract

Darwin與McArthur提出的經典理論認為，物種分布的限制因子會受到外在環境所影響，山區物種的分布下界主要受到種間競爭的交互作用（competitive interaction）所限制，分布上界則主要受到非生物因子的限制。本研究以尼泊爾埋葬蟲（Nicrophorus nepalensis）與紅胸埋葬蟲（Calosilpha chyaneocephala），兩種擁有不同棲位寬度的屍食性埋葬蟲科（Silphidae）甲蟲為目標物種，探討非生物因子以及生物因子對物種海拔分布的重要性。本研究地點位於臺灣中部橫貫公路，時間為 2011 到 2013 年的七月到九月，沿海拔梯度設置腐肉陷阱，記錄埋葬蟲於陷阱中的出現機率及繁殖成功率。結果顯示紅胸埋葬蟲出現機率與繁殖成功率沿每日最高溫有相同趨勢，顯示非生物因子為紅胸埋葬蟲海拔分布上界與下界的限制因子。尼泊爾埋葬蟲的出現機率與繁殖成功率在每日最低溫上卻有不一致的趨勢，且繁殖成功率顯著低於出現機率。結果顯示單獨氣候因子無法解釋尼泊爾埋葬蟲於海拔分布的邊界。藉由室內實驗，證實尼泊爾埋葬蟲在海拔上界受非生物因子的限制，而下界則受蒼蠅競爭的限制。不同於過去研究，本研究發現物種的棲位寬度能更完整的解釋物種在海拔分布限制因子的種類：對廣棲性物種（habitat generalist）而言，限制其海拔分布上界與下界皆為氣候因子；對狹棲性物種（habitat specialist）而言，其海拔分布上界是受氣候因子的限制，但下界的限制因子則是生物因子。了解生物在海拔分布的限制因子，不僅能了解物種現今的分布模式，也有助於我們預測生物面對環境變遷的反應。

Darwin(1859) and McArthur’s (1972) classic hypothesis for the elevation range limit stated that competitive interaction drives the lower elevation range limits of montane species, and physiological stress prevents low-elevation species from expanding to high elevation. However, factors that limit species’ elevation range are still poorly understood. We tested McArthur’s hypothesis of elevation range limits in two carrion beetles with distinct life history traits: Nicrophorus nepalensis, a habitat specialist, and Calosilpha cyaneocephal, a habitat generalist. We found that physiological constrains drive the lower and higher elevation range limit of C. cyaneocephal, whereas competition with maggots was found responsible for the lower limit of elevational range of N. nepalensis. Contracting to McArthur’s classic hypothesis, our findings show that different life history traits between species may explain the different constrains in lower elevation range limit: habitat specialists may be more susceptible to biotic factor than habitat generalists. Our study of elevation range limit can help us understand species distribution pattern and better predict the species responses to climate change.