鰓足類動物在暫時性池塘之空間棲位分化及光度影響

Abstract

陽明山國家公園內的向天池是藉由颱風造成的大規模降雨而形成的暫時性池塘，其積水期高度不可預期，且維持時間短暫又具有相當大的變異。池中有三種鰓足類動物：湖沼枝額蟲(Branchinella kugenumaensis)、真湖蚌蟲(Eulimnadia sp.)與貓眼蚌蟲(Lynceus biformis)；牠們如何減緩種間競爭壓力以達成共域共存，是本論文的研究焦點。研究內容分為兩部分，首先是調查野外池水中這三種的三度空間分佈模式，並探討三種之間空間棲位利用分化的可能性與方式（第二章）。野外調查在2008年六月到十月期間颱風後的兩次積水期密集進行採集，並進行各採樣點密度估算。研究發現不論在水平或垂直的面向分析，牠們均有顯著的空間分化現象：水平面向傾向隨機性的組合且每日變換，而垂直面向則是各種有其特定的分佈區域，其中以湖沼枝額蟲主要聚集於最上層，貓眼蚌蟲則主要掌控中下層的優勢。第二部分的內容是探討光線強度對這三種共域的鰓足類動物空間分佈的影響，另外也進行實驗室內養殖，測試鰓足類動物的趨光性反應（第三章）。研究發現在實驗室操控光度20-22,610 Lux的範圍內時，人工孵化出的兩種鰓足類：湖沼枝額蟲和真湖蚌蟲，皆有顯著的正向趨光反應。然而當分析野外這三種鰓足類動物的空間分佈與自然光線(範圍：1,548-96,000 Lux)的關係時，趨勢變的較為複雜；其中，湖沼枝額蟲傾向聚集在強光處，而真湖蚌蟲與貓眼蚌蟲則較傾向於弱光處。最後探討造成空間分布的機制以及後續研究的方向。

Siangtian Pond, located in the Yangmingshan National Park, is an ephemeral pool that typically forms after the torrential rains of a typhoon. The inundation period is highly unpredictable, short-lived, and with pronounced variation. Three species of branchiopods inhabit the pool, including Branchinella kugenumaensis, Eulimnadia sp. and Lynceus biformis. This study focused on how the sympatric branchiopods achieved coexistence by reducing the interspecific competition stress. There are two major parts: the first one focused on the distribution patterns of these three branchiopods in the field, and investigated the possibility and mechanism of spatial niche differentiation among them (Chapter Two). The results showed that there was significant separation in spatial distribution in both horizontal and vertical views. Random hot-spotting that changed with time was observed in the horizontal dimension, but relative fixed stratification in the vertical dimension. While fairy shrimp B. kugenumaensis gathered in the superficial layer, clam shrimp L. biformis increased dominance in the bottom layers. The second part explored the influence of light intensity on the spatial distribution of these branchiopod populations (Chapter Three). In addition, we conducted laboratory experiments to clarify their phototaxis reactions. The results demonstrated that both B. kugenumaensis and E. sp. showed significantly positive phototaxis under the laboratory culture setting with illumination ranged from 20 to 22,610 Lux. However, the photo-responses were more complicated when analyzing the branchiopods’ spatial distribution in natural light intensity (ranging from 1,548 to 96,000 Lux). B. kugenumaensis mainly aggregated in higher illuminations, while E. sp. and L. biformis clumped more in lower illuminations. To conclude, we discussed the mechanisms that might result in the spatial distribution of these branchiopods and considered the directions of future studies.