| 摘要: | 在過去的二十年之中，因意識到生物多樣性的急速流失，許多生態研究紛紛投入探索生物多樣性降低對於生態系造成的衝擊。然而直至今日，要精確預測生物多樣性降低對於生態系造成的影響仍充滿許多挑戰。這主要是因為生物多樣性的效應嵌植在複雜的交互作用網路中，而生態學家對於這些複雜的交互作用網路仍缺乏完整且準確的了解。一方面，基於操弄性實驗的研究雖然成功地展現了生物多樣性對於生態系功能的正面影響，但由於實驗操作之侷限性，使得該類研究僅能在高度簡化的系統中探索不完整、單方向的生物多樣性之因果關係；另一方面，基於實測資料分析的研究總會因使用線性分析(如相關性分析、迴歸分析與結構方程式等)而無法推論在生態系這類的非線性動力系統中的因果關係。因此在這篇論文中，我將利用經驗動態方程分析重建在自然浮游植物群聚中，以物種多樣性、生態系功能以及環境因子所組成的因果關係網路。透過跨系統的網路分析比較，我首先確認了生物多樣性與其他生態系單元(像是生物量或是營養鹽)之間的交互作用是廣泛存在於自然的水域生態系統(第二章)。為了探索這些交互作用在生態系扮演的角色，我提出了一個新的理論模型，並且揭露了這些交互作用將使得生物多樣性對於生態系具有動態穩定效應(第三章)。接著，我利用野外收集的實測資料驗證了生物多樣性的動態穩定效應，並且發現了該穩定效應如何隨氣候暖化而被削弱(第四章)。最後，因考慮到這些以生物多樣性為中心的複雜交互作用，我提出了一個新的經驗動態方程的分析方法，用來評估在自然系統中生物多樣性降低對於生態系功能所造成的衝擊(第五章)。在這篇論文中，我突顯了生物多樣性之動態行為所扮演的角色，也就是生物多樣性的本身、對環境的反應、並且對生態系的影響都會隨時間及系統的狀態而有所改變。因此，相較於過去將多樣性效應獨立出來的研究，我們發現考慮多樣性與其他生態系單元之間的交互作用更能幫助我們理解生物多樣性在生態系層級下的穩定性機制。總結，我的論文提出了一個在考量動態交互網路下研究生物多樣性-生態系功能的新範式。;The awareness of biodiversity loss stimulates amounts of studies to explore the ecosystem consequence of biodiversity loss in the past two decades. However, forecasting the consequence of biodiversity loss in natural ecosystems is still challenging because the effects of biodiversity on ecosystem functioning is embedded in a complex network of ecosystems components with mutual interactions and these are poorly understood. On the one hand, although the experimental studies have successfully demonstrated the positive influence of biodiversity on ecosystem functioning, these experiments can only reveal incomplete unidirectional causality of biodiversity under highly simplified environmental context. On the other hand, the studies based on empirical data analyses face the problem that linear analyses (correlation, regression, structure equation modeling, etc.) cannot reveal causation in nonlinear dynamical systems, such as ecosystems. In this thesis, I apply empirical dynamical modeling (EDM) to construct the causality network among species diversity, ecosystem functioning, and environmental factors in natural phytoplankton communities. Through the cross-system analysis of the networks, I firstly recognize the prevalence of the diversity-mediated mutual interactions in natural ecosystems (Chapter 2). To explore the ecological roles of these mutual interactions, I propose a novel theoretical dynamical model which reveals the dynamical stabilizing effects of biodiversity via the mutual interactions between diversity and the other parts of dynamical ecosystem (Chapter 3). Moreover, I empirically test this dynamical stabilizing effects in natural aquatic ecosystems and demonstrate how these stabilizing effects weakened under climate warming (Chapter 4). Finally, by acknowledging the complexity of diversity-associated interaction network, I propose a new EDM method to evaluate the realistic consequence of biodiversity loss that account for environmental context (Chapter 5). In brief, I highlight the reality that diversity is one of the key components in dynamical ecosystems, and its dynamics, responses, and impacts are time-varying and context dependent. Therefore, studying the diversity effects embedded in dynamical interaction network is more helpful to understand the stabilizing mechanisms of biodiversity than studying the diversity effects in isolation. In conclusion, a new biodiversity-ecosystem functioning paradigm emerges from my thesis concerning the dynamical interaction networks. |
