Habitat fragmentation changes top-down and bottom-up controls of food webs.

Top-down and bottom-up controls regulate the structure and stability of ecosys tems, but their relative roles in terrestrial systems have been debated. Here we studied a hydro inundated land-bridge system in subtropical China and tested the relative importance of thesetwo controls in determining the rodent-mediated regeneration of a locally dominant tree spe cies. Our results showed that both controls operated in terrestrial habitats and that their rela tive importance switched as habitat size changed.

自上而下控制（top-down control）与自下而上控制（bottom-up control）共同调控生态系统的结构与稳定性，但二者在陆地生态系统中的相对作用长期存在学术争议。本研究以中国亚热带地区一处洪水淹没的陆桥系统为研究对象，探究这两种调控方式在决定本土优势树种的啮齿动物介导更新过程中的相对重要性。研究结果显示，两种调控方式均在陆地生境中发挥作用，且其相对重要性会随生境面积的变化发生转变。