臺灣兩種鼠科物種在時空棲位的區隔

Abstract

根據競爭互斥原理(competitive exclusion principle)，在兩物種具強烈競爭關係的前提下，應會進行棲位區隔(niche partitioning)，以利穩定共存。臺灣森鼠(Apodemus semotus)及高山白腹鼠(Niviventer culturatus)為棲息於臺灣山區的夜行性、雜食性優勢鼠科(Muridea)物種。過去觀察資料顯示，高山白腹鼠較臺灣森鼠更傾向使用森林棲地，因此我推論空間棲位區隔，特別是對非地面棲地的使用，是兩物種共存的機制之一。此外，我預測兩物種在時間棲位上可能也會有區隔，不同時間與不同空間(地面棲地、非地面棲地)可能在微氣候、食物豐度、掠食壓力等方面條件都不同，因此當物種間有空間棲位上的差異時，可能會連帶反應到時間棲位上的差異；此外，高山白腹鼠與臺灣森鼠有相當的形值差異，可能具不同之體溫調節能力、新陳代謝效率與被掠食風險等，進而直接影響時間棲位的利用。本實驗利用被動式晶片掃描器及紅外線自動相機量化兩物種在水平、垂直的空間棲地以及夜晚不同時段的使用頻度，據此估算兩物種的棲位寬度與重疊度，並透過null models推論兩物種間是否有棲位區隔。同時，我進一步將時空棲位與環境溫度整合，進行多維度棲位區隔檢定。本實驗於2017年至2018年在臺灣南部山區的向陽國家森林遊樂區進行。結果顯示，高山白腹鼠較臺灣森鼠傾向使用非地面棲地，但兩物種在上、下半夜皆有相當的使用。將空間、時間棲位及溫度棲位維度合併分析的結果顯示，兩物種不具棲位區隔。本研究成果有助於釐清臺灣山區優勢鼠科物種共存之機制。Following the competitive exclusion principle, niche partitioning between species under strong competition should facilitate stable coexistence. Apodemus semotus and Niviventer culturatus, both nocturnal and omnivorous, are two dominant murids in the montane region of Taiwan. Based on observational data, N. culturatus appear to use forest habitats more frequently than A. semotus. Therefore, I hypothesize that spatial niche partitioning between ground and arboreal habitats play a role in their coexistence. Furthermore, I also predict temporal niche partitioning between A. semotus and N. culturatus. Because different times and space (e.g. ground or arboreal) could represent different environmental conditions in microclimate, food availability and predation risk, temporal niche partitioning could occur as a byproduct of spatial niche partition or directly via mechanisms such as differential thermoregulation, metabolism and predation risk, the latter of which is particularly plausible for species that differ in morphology. In this study, I used RFID (Radio Frequency Identification) tagging and field infrared cameras to quantify the frequencies of use among different time periods throughout the night and different spatial locations (horizontal locations as well as ground versus arboreal habitats). Based on these data, I estimated the niche width for each species and the niche overlap between the species. Niche partitioning was tested by comparing the observed niche overlap with the null distribution of permutated niche overlaps. I also combined spatiotemporal niche with temperature niche to explore the partitioning of these two species in multidimensional niche space. The study was conducted from 2017 to 2018 at Siangyang Forest Recreation Area in southern Taiwan. The results indicated that N. culturatus used arboreal habitats more than A. semotus whereas both species overlapped extensively in their horizontal space use and temporal niche. In multidimensional niche space, A. semotus and N. culturatus also did not exhibit niche partitioning. This study contributed to our understanding of potential coexistence mechanisms between two dominant murids in Taiwan’s montane ecosystem.