Data from: Density-dependent movement and the consequences of the Allee effect in the model organism Tetrahymena

1. Movement and dispersal are critical processes for almost all organisms in natural populations. Understanding their causes and consequences is therefore of high interest. While both theoretical and empirical work suggests that dispersal, more exactly emigration, is plastic and may be a function of local population density, the functional relationship between the underlying movement strategies and population density has received less attention. 2. We here present evidence for the shape of this reaction norm and are able to differentiate between three possible cues: the relative number of individuals, the presence of metabolites (chemical cues) and resource availability. 3. We performed microcosm experiments with the ciliate model organism Tet-rahymena in order to understand the plasticity of movement strategies with respect to local density while controlling for possible confounding effects mediated by the availability of different cues. In addition, we investigated how an Allee effect can influence movement and dispersal plasticity. 4. Our findings suggest that movement strategies in Tetrahymena are plastic and density-dependent. The observed movement reaction norm was ushaped. This may be due to an Allee effect which led to negative densitydependence at low population densities and generally positive density-dependence at high population densities due to local competition. This possibly adaptive density-dependent movement strategy was likely mediated by chemical cues. 5. Our experimental work in highly controlled conditions indicates that both environmental cues as well as inherent population dynamics must be considered to understand movement and dispersal.

1. 运动与扩散是自然种群中几乎所有生物的关键生命过程。阐明其驱动机制与生态后果因此具有重要研究价值。现有理论与实证研究均表明，扩散（更确切地说为迁出行为）具有表型可塑性，且可能随局域种群密度发生变化，但关于潜在运动策略与种群密度间的函数关系，相关研究仍较为匮乏。
2. 本研究提供了该反应规范（reaction norm）的形态学证据，并可区分三类潜在调控线索：个体相对数量、代谢物（化学信号）的存在状态，以及资源可获得性。
3. 本研究以纤毛虫模式生物四膜虫（Tetrahymena）为研究对象开展微宇宙实验，旨在解析局域密度梯度下运动策略的表型可塑性，同时控制由不同线索可获得性介导的潜在混杂效应。此外，本研究还探讨了阿利效应（Allee effect）如何影响运动与扩散可塑性。
4. 研究结果表明，四膜虫的运动策略具有表型可塑性且呈密度依赖特征。观测到的运动反应规范呈U型分布，这可能由阿利效应介导：在低种群密度下表现为负密度依赖，而在高种群密度下因局域竞争作用通常表现为正密度依赖。这种具有潜在适应性意义的密度依赖型运动策略，大概率由化学信号所调控。
5. 本研究在高度可控的实验条件下开展的工作表明，若要全面理解运动与扩散过程，需同时兼顾环境线索与内在种群动态两方面因素。