亞熱帶森林源頭溪流哈盆溪食物網之研究－穩定碳氮同位素分析之應用

Abstract

本研究針對哈盆溪食物網中的主要物種，以穩定同位素分析法探討溪中水生生物的碳源及營養階層，並輔以消化道內含物分析法探討台灣馬口魚成魚在不同季節的攝食狀況及成長過程中的食性變化。 溪流生物的主要碳源來自沿岸植物枯落物之異生性輸入(δ13C=-33.0??-28.0?), 及水中小型藻的自生性輸入(δ13C=-23.3??-22.5?)。水中有機顆粒之δ13C平均值為-29.2?,推測其主要來自沿岸植物。依二端點混合模式估算，66.6％的初級消費者碳源(>50%)主要倚賴異生性輸入，53.8％的高階消費者碳源(>50%)主要倚賴異生性輸入。哈盆溪食物網的營養輸入分析顯示，沿岸植被是影響溪流能量輸入的重要因數。但26.3％的消費者，其碳源超過70％倚賴自生性的輸入，此現象可能和快速生長的藻類有關。哈盆溪食物網有4個營養階層，台灣馬口魚為最高階的消費者。 由消化道內含物之分析結果得知，台灣馬口魚的主要食物為水棲昆蟲、陸棲昆蟲及甲殼類。成魚攝食隨季節變化，傾向機會主義的通食者。穩定同位素分析進一步顯示，台灣馬口魚成魚主要利用捕食性的水棲昆蟲及沿岸陸棲昆蟲。台灣馬口魚在個體發育的過程中，呈現食性變化，全長40mm以上的個體，利用陸樓昆蟲的比例增加，全長100mm以上的個體，食物中甲殼類所佔比例增加。穩定同位素分析顯示，台灣馬口魚全長增加至20mm以上後，其營養階層增加0.4階。

In the Hapen Creek, a subtropical woodland headwater area, we used stable isotope analyses and gut analyses to examine the food web structure. The objectives included (1) analyze the fate of allochthonous and autochthonous sources of organic matter in the aquatic food web, (2) elucidate the trophic interactions among consumers, (3) temporal diet change of adult Candidia barbata, a dominant fish in this area, (4) ontogenetic dietary shift of C.barbata. The major sources of organic carbon available to consumers were the allochthonous input of riparian vegetation litter (meanδ13C：-33.0? to -28.0?）and autochthonous input of microalgae (meanδ13C: -23.3? to -22.5?). A two-source mixing model indicated that, allochthonous carbon comprised >50% of tissue carbon for 66.6% aquatic primary consumers analysed, and comprised >50% of tissue carbon for 53.8% aquatic higher-order consumers analysed. For the maintenance of aquatic food webs, preserving riparian vegetation is important in habitat managements. However, 26.3% consumers utilized higher proportions of autochthonous carbon (>70%) than those in temperate streams. Increasing utilization of autochthonous carbon suggests the presence of high autochthonous productivity. The longest food chains of the Hapen food web had 4 trophic levels, and C. barbata. were at the highest level. Gut analyses indicated that the main food of C. barbata. were aquatic insects, terrestrial insects, and crustaceans. The diet of adult C. barbata exhibited seasonal variations. Thus C. barbata are opportunistic generalists. Furthermore, stable isotope analyses revealed that C. barbata mainly utilize aquatic insects and terrestrial insects. Both gut analyses and stable isotope analyses revealed the ontogenetic dietary shift of C. barbata. Assuming a δ15N enrichment of 3.4? per trophic level, C. barbata were found to increase its trophic position by 0.4 trophic level as they grew from < 20 mm to > 20 mm in total length.