台大海洋研究所的研究團隊利用測量浮游動物大小和群落結構的新技術，提出了一個全新的假說：掠食者體型多樣性的增加會促使獵物階層的食性棲位（diet niche）分化，進而強化系統中對獵物的下行控制（top-down control）。在實證研究上，這個假說獲得東海浮游生物數據的支持。此研究是由海洋研究所的博士後研究員葉麟，和謝志豪副教授所進行，發表於2013年3月號的動物生態學期刊（Journal of Animal Ecology）。
Lin Ye and Chih-hao Hsieh
Institute of Oceanography, National Taiwan University
With the aid of new technologies to measure zooplankton size and community structure, a group of scientists of National Taiwan University formulated a novel hypothesis: increasing predator size diversity enhances the strength of top-down control on prey through diet niche partitioning, and this hypothesis was supported empirical plankton data in the East China Sea. This work is led by the postdoctoral researcher Lin Ye, and associate professor Chih-hao Hsieh and is published in the Journal of Animal Ecology (March 2013).
Understanding the relationship between biodiversity and ecosystem functioning is a pressing concern in ecosystem management. Traditional metrics to quantify biodiversity focus on species diversity. However, accumulating evidence suggests the importance of considering functional diversity. In this work, we employed the well-established argument that size represents the most important functional trait in aquatic ecosystems. Indeed, many studies have shown that body size of organisms is sensitive to environmental changes and is one of the fundamental characteristics of organisms linking many ecosystem properties. Here, we proposed to use size diversity to represent the critical diet niche diversity and developed a novel theory that increasing zooplankton size diversity enhances the strength of top-down control on phytoplankton through diet niche partitioning. This mechanism can be explained by the optimal predator-prey body-mass ratio concept. Suppose each size group of zooplankton predators has its own optimal phytoplankton prey size, increasing size diversity of zooplankton would promote diet niche partitioning of predators and thus elevates the strength of top-down control.
To test this theory, we collected plankton samples and environmental variables in the East China Sea. We used a newly developed semi-automatic zooplankton classification system to measure zooplankton size and community structure. Our theory is supported with empirical data from the East China Sea. This work points out an important research direction to consider size structure in studies of trophic interactions. This work is an outcome of the largest interdisciplinary ocean ecosystem research project in Taiwan: Long-term Observation and Research of the East China Sea (LORECS).
References
Ye, L., C. Y. Chang, C. García-Comas, G. C. Gong, and C. H. Hsieh (2013) Increasing zooplankton size diversity enhances the strength of top-down control on phytoplankton through diet niche partitioning. Journal of Animal Ecology. doi: 10.1111/1365-2656.12067
Ye, L., C. Y. Chang, and C. H. Hsieh (2011) Bayesian model for semi-automated zooplankton classification with predictive confidence and rapid category aggregation. Marine Ecology Progress Series. 441: 185-196
Figure 1. Conceptual diagram summarizing the size diversity hypothesis: the mechanism of increasing predator size diversity enhancing the strength of top-down control on prey through diet niche partitioning. Panel A indicates that the community with a low size diversity can only forage on a rather narrow diet niche breadth; by contrast in panel B, the community with a high size diversity can have a rather evenly and widely distributed diet niche breadth. The dash line represents conceptually the predation pressure of a given size class.
Figure 2. ZooScan: zooplankton imaging and classification system.
Figure 3. Schematic illustrating automatic computer-aided zooplankton classification system.
在生態系統管理上，目前急需了解生物多樣性和生態系功能之間的關係。傳統生物多樣性的量化指標多偏重於物種多樣性，然而越來越多的證據顯示功能多樣性更為重要。事實上，許多研究顯示生物的體型大小對環境變化極為敏感，是連結個體至生態系屬性的基本特性。此研究延續體型大小是水生生態系中最重要的功能特性的論點，以體型大小的多樣性來代表最重要的食性棲位多樣性，並由此發展一新理論：掠食者體型多樣性的增加會促使食性棲位分化，進而強化系統中對獵物的下行控制（top-down control）。這個機制可以由掠食者與獵物最適身體質量比的概念來解釋。首先，將全部的浮游生物皆以體型來分組，假設每組掠食者浮游動物都有其最適當的浮游生物獵物大小，那麼增加浮游動物的體型多樣性便會促進獵物階層的食性棲位分化，從而強化下行控制。
研究團隊以東海浮游生物與該處環境變數來驗證此理論。他們利用新開發的半自動化浮游動物分類系統來測量浮游動物的大小和群落結構，結果實證研究的結論確實與理論預測吻合，這也顯示出在研究食性位階的交互作用時，需要考慮體型大小的組成結構。這項研究來自於台灣規模最大的跨領域海洋生態系統研究計畫：東海長期觀察和研究（LORECS）。
References
Ye, L., C. Y. Chang, C. García-Comas, G. C. Gong, and C. H. Hsieh (2013) Increasing zooplankton size diversity enhances the strength of top-down control on phytoplankton through diet niche partitioning. Journal of Animal Ecology. doi: 10.1111/1365-2656.12067
Ye, L., C. Y. Chang, and C. H. Hsieh (2011) Bayesian model for semi-automated zooplankton classification with predictive confidence and rapid category aggregation. Marine Ecology Progress Series. 441: 185-196
Figure 1. Conceptual diagram summarizing the size diversity hypothesis: the mechanism of increasing predator size diversity enhancing the strength of top-down control on prey through diet niche partitioning. Panel A indicates that the community with a low size diversity can only forage on a rather narrow diet niche breadth; by contrast in panel B, the community with a high size diversity can have a rather evenly and widely distributed diet niche breadth. The dash line represents conceptually the predation pressure of a given size class.
Figure 2. ZooScan: zooplankton imaging and classification system.
Figure 3. Schematic illustrating automatic computer-aided zooplankton classification system.
