食物链长度远因与近因研究进展综述

Proximate and ultimate determinants of food chain length

食物链长度是生态系统的基本属性,其变化决定着群落结构和生态系统功能。稳定同位素分析技术的进步推进了生态系统中食物链长度决定因子相关研究的开展。尽管近期的研究证明了食物链长度与资源可利用性、生态系统大小、干扰等远因之间的关系,但是对于食物网内部结构变化这一近因对食物链长度的影响作用关注较少。综述了边界明确和开放类型淡水生态系统中食物链长度的相关研究进展;探讨了远因和近因机制在决定食物链长度中的作用;给出了判断不同层次和尺度上决定食物链长度机制的概念框架;为今后更好的开展不同生态系统间食物链长度的比较研究提出了建议。

Food chain length has been recognized as an important ecosystem characteristic and a fundamental ecosystem attribute： it influences community structure, ecosystem functions and bioaccumulation of contaminants in top predators. Previous studies have shown that food chain length varies greatly among systems. Defining the determinants of food chain length has been a primary research focus for food web ecologists, and has contributed to ecological theories. Three main hypotheses, i.e. resource availability, ecosystem size, and the disturbance hypothesis, which argues that the stability of local dynamics and the level of disturbance contribute to food chain length have been extensively examined. However, much less attention has been paid to proximate changes in food web structure that link variation in food-chain length to the ultimate dynamic mechanism. Proximate mechanisms could cause variation in food-chain length by either： additive mechanism, through addition or removal of top predators; insertion mechanism, through addition or removal of intermediate predators; omnivory mechanisms, changes in the degree of trophic omnivory by the top predator. Recent advances in stable isotope analysis have rekindled interest in examining factors that determine food chain length in ecological communities. In this paper, we reviewed recent studies from close and open freshwater systems to explore the factors that determine the relative importance of resource availability, disturbance and ecosystem size on food chain length, and how they may be affected by food web architecture. We then provided a framework to investigate how these hypotheses operating at different spatial scale. We explore the implications of these mechanisms for understanding how proximate changes in food-web structure link variation in food-chain length to the ultimate mechanism. Finally, we gave suggestions in applying the framework to consolidate the hypotheses across ecosystems in future studies.