摘要:生產力為決定生態系中食物網效率與生地化循環的基本參數,而研究生產力是否會隨環境變化而發生改變,一向是生態學中的重要課題。傳統生態觀點(生物多樣性模式)認為多樣性會影響生產力,尤其是高生產力和高度多樣性常有相關,並認為此種現象很可能是透過機能組合效應(portfolio effects)來達成。然而, 生物多樣性模式預測與實測結果並不完全一致,也缺乏對生產力定量的預測。反觀近來生態學中代謝理論(MTE模式)的進展顯示,生產力主要受到體型大小與環境溫度的影響: 。在此式中P代表生產力,M表示體型大小,E則是活化能,K為波茲曼常數,而T則代表絕對溫度。MTE模式認為群聚是由許多大小相似的個體組成,忽略物種的觀念,而此種觀點也逐漸得到實證支持。不過,模式驗證的結果卻常不盡如人意。此兩種模式皆是基於基礎生態理論發展而成,因此先前研究多半都是以理論為主 。
本研究希望評估生物多樣性和代謝模式對海洋浮游食物網的生產力之相對解釋程度。本研究著重海洋浮游生物,因為營養階層互動關係在海洋生態系中多半與體型大小有關,且浮游生物在海洋中的多樣性高,其生產力的量測也已建立標準流程。本研究預計在環境變化梯度下,量測浮游細菌、浮游植物與浮游動物的多樣性、生物量與生產力,我們強調研究對象涵蓋不同營養階層與體型大小頻譜。本研究檢驗以下三個假說:H1 多樣性決定生產力;H2 體型大小與溫度決定生產力;H3 多樣性與MTE模式共同決定不同營養階層的生產力,而H0則是假設生產力獨立於多樣性、體型大小與溫度三者。此項研究結果將有助於了解海洋浮游食物網中的生態過程。
另外,本研究將利用以下方程式來驗證MTE模式在食物網層級中的實用性:log(N)=(log(TE)/log(PPMR)-0.75)*log(M),其中N代表某一體型相似生物群的豐度,M表示該生物群,而TE則是營養階層間的傳遞效率,PPMR為捕食者與獵物之體型大小比例。此一概念在理論上已有嚴謹探討,但從未由實測證實。除驗證假說外,本研究結果亦能進一步釐清群聚結構(多樣性、均勻度、優勢種、物種組成、體型大小分佈)在不同營養階層間如何即時反應環境變異。並由透過量測生產力來了解生地化循環受環境變動之影響。
本研究的主要目標,在於建立結合生物多樣性與基於食物網的MTE模式,並以實測資料檢驗。由於全球暖化與人為污染不僅會影響海水溫度,也極可能會改變體型大小與群聚結構,而生產力的變化可能將對更高食階-如可用的漁業資源產生重大影響,故此項研究結果對於環境變遷下的海洋生態系管理應有所助益。 本研究為整合型計畫: 『全球變遷對西北太平洋臺灣海域 海洋生物地球化學與生態系統影響之長期觀測與研究』之一環。
Abstract: Biological production is a fundamental parameter determining foodweb efficiency and biogeochemical cycling in ecosystems. Investigating whether and how biotic production rates respond to environmental changes (such as pollution and climate warming) plays a central role in ecology. Classic ecological models (biodiversity model) indicate that diversity may affect production. Particularly, high production rate is often correlated with high diversity, likely through functional portfolio effects. However, empirical studies do not show unanimous results, and there is no quantitative prediction of production based on diversity. By contrast, recent advances in metabolic theory in ecology (MTE model) suggest that production rate is dependent mainly on organism body size and environmental temperature: , where P is production, M is the body size, E is activation energy, K is the Boltzmann’s constant, and T is the absolute temperature. Such MTE model, considering a community consisting of organisms with similar size and ignoring species concept, also gains substantial empirical support. However, the model fit is often not satisfactory. Both models are derived from fundamental ecological principles, and theoretical studies abound; however, their relative contribution in explaining the biological production is never evaluated.
Here, we propose to evaluate the relative strength of biodiversity and metabolic model in explaining biological production in marine plankton foodwebs. We focus on marine systems because trophic interactions are usually size dependent in marine ecosystems; we focus on plankton, because marine plankton encompass a huge diversity and their production can be quantified using standard methods. To demonstrate the concept, we aim to measure simultaneously diversity, biomass, and production of bacterioplankton, phytoplankton, and zooplankton from different trophic levels with a large range of size spectrum across a gradient of environmental variations. We test the hypothesis that H1: diversity determines production; H2: size and temperature determines production; and H3: diversity and MTE model jointly determine production across trophic levels, against the H0 that production is independent of either diversity or size and temperature. These results potentially move forward our understandings of ecological processes.
In addition to testing the hypotheses, those measurements help us understand the community structure (diversity, evenness, dominance, species composition, size distribution) simultaneously across trophic levels in response to environmental variation. Moreover, the production measurements allow us to investigate biogeochemical cycling in response to environmental changes. Furthermore, we test the MTE model in a foodweb context by deriving the equation: log(N)=(log(TE)/log(PPMR)-0.75)*log(M), where N is abundance of a biomass class, M is biomass class, TE is trophic transfer efficiency, and PPMR is predator-prey mass ratio. Such concept, although is stringently discussed in theoretical literature, is never tested empirically.
The main objective here is to integrate and test empirically the biodiversity and MTE model in a foodweb context. Our results have strong implications to marine ecosystem management under environmental changes, because climate warming and anthropogenic pollution is likely to affect size and community structure as well as ocean temperature. Affected production rates may have critical impacts on higher trophic levels such as fisheries production availability. Our project is part of the interdisciplinary project: Effects of Global Change on Ocean Biogeochemistry and Ecosystems in the Seas surrounding Taiwan in the Northwest Pacific (ECOBEST).