浮游植物關聯群聚的空間β 多樣性在翡翠水庫上游水域之時間變化

Temporal change of spatial beta diversity in phytoplankton metacommunity of Feitsui Reservoir and its upstream

林樸仁(Pu-Jen Lin)

指導教授 ： 謝志豪

國立臺灣大學/理學院/海洋研究所/碩士(2021年)

https://doi.org/10.6342/NTU202104531

摘要

空間beta 多樣性(spatial beta diversity)是生態學的重要議題之一。其中旨在研究關聯群聚 (metacommunity) 的空間結構，包括對 beta 多樣性的模式及其驅動因子的分析。然而，過去很少有研究檢驗空間beta 多樣性是如何隨時間而改變。本研究重點在分析過去19 年來翡翠水庫及其上游浮游植物beta 多樣性結構及其驅動因子的時間變化。我們假設站點之間的空間成對環境差異是空間成對 beta 多樣性的重要驅動因子。亦即，beta 多樣性的時間變化主要由環境差異的時間變化而決定。為了檢驗我們的假設，我們首先按照基於 Sørensen 的 Baselga 方法計算了每個年月的所有成對總 beta 多樣性(pairwise total beta diversity)，並將其拆分為周轉(turnover)和嵌套(nestedness)多樣性。因此，對於每個年月，我們有三個 beta 多樣性指標：總 beta、周轉和嵌套多樣性。然後，使用變異劃分方法(variation partitioning)來量化每個年月中環境差異和空間距離對於每個beta多樣性指標的相對貢獻，以顯示它們各自對每個月beta 多樣性的重要程度。最後，我們對每個成對站點在每個月份的 19 年間 Beta 多樣性和環境差異的值取平均，並使用此長期平均每月站點間環境差異來對長期平均每月 beta 多樣性回歸以顯示 beta 多樣性的季節性變化是否對應於環境差異的季節性變化。我們的結果顯示，三個 beta 多樣性指標表現出明顯的月際（季節性）變化，其中3 至 5 月的值較高，且無明顯長期趨勢。變異劃分的結果指出，在每個月份，總beta 和周轉多樣性可以用環境差異和地理距離來解釋，但環境差異的影響更重要，尤其是水溫，在多數的月份都有顯著的影響。然而，在長期平均中，雖然觀察到長期平均每月站點間環境差異與長期平均每月 beta 多樣性之間存在正相關，但beta 多樣性和環境差異的月際變化並不一致。具體而言，beta 多樣性在3到5月較高，但總環境差在5到9月較大。而二者的不一致性主要是由於兩個原因所致。首先，beta多樣性對環境異質性的反應在各個月並不相同。再者，不同月份的環境差異解釋力不同。總而言之，翡翠水庫浮游植物的beta 多樣性在整個研究期間表現出季節性變化，但其季節性波動並不單純由環境差異決定。

關鍵字

Beta 多樣性 ； 浮游植物 ； 關聯群落 ； 時間變化

並列摘要

Beta diversity is one of the major topics in ecology. Many studies have focused on spatial metacommunity, including analyses of beta diversity patterns and their drivers. However, very few empirical studies examined how spatial beta diversity varied over time. The aim of this study is to provide insight into the temporal variation of beta diversity structures of phytoplankton and its drivers in Feitsui Reservoir and its upstream in the past 19 years. We hypothesized that the spatial pairwise environmental difference between sites is generally an important driver determining spatial pairwise beta diversity through time. That is, the temporal variation of beta diversity was mainly determined by the temporal change of environmental difference. To test our hypothesis, we first calculated all of the pairwise total beta diversity for each year-month and decomposed it into the turnover and nestedness compartments, following the Sørensen-based Baselga’s approach. As such, for each year-month, we obtained three beta diversity indices: total beta diversity, turnover, and nestedness. Then, for each beta diversity index, variation partitioning was used to quantify the relative contributions of environmental difference and spatial distance in each year-month to show their respective importance to each month’s beta diversity in general. Finally, we took average across 19 years of beta diversity and environmental difference for each month (Jan, Feb, …, Dec) for each paired sites, and the long-term averaged monthly beta diversity was used to regress against the long-term averaged monthly total environmental difference between sites to show whether the seasonal variation of beta diversity is corresponding to the seasonal variation of environmental difference. Our results indicate that the three beta diversity indices exhibited clear monthly (seasonal) variation, with high values from March to May, but no clear long-term trend over the years. The results of variation partitioning indicated that total beta diversity and species turnover can be explained by environmental differences and geographic distance in each month, but environmental differences were relatively more important. Moreover, the difference of water temperature between sites showed significant effect on beta diversity in most calendar months. However, in long-term average, although the positive relationship between long-term averaged monthly total environmental difference and long-term averaged monthly beta diversity was observed, the monthly variation of beta diversity and environmental difference were not consistent. Specifically, beta diversity was higher from March to May, but total environmental difference was higher during May to September. This inconsistency in long-term average is mainly due to two reasons. First, the response of beta diversity to environmental heterogeneity was not the same among calendar months. Second, the explanatory power of environmental difference was distinct in different calendar months. In general, the beta diversity of phytoplankton in Feitsui Reservoir exhibited seasonality across the study period, but its seasonal fluctuation was not exclusively determined by the level of environmental difference.

並列關鍵字

Beta diversity ； Phytoplankton ； Metacommunity ； Temporal variation

參考文獻

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