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态过程。解析其成因与后果具有重要研究价值。现有理论与实证研究均证实，扩散（更确切地说是迁出）具有表型可塑性，且可能为局域种群密度的函数，但潜在运动策略与种群密度之间的函数关系却较少受到关注。
2. 本研究提供了该反应规范（reaction norm）形态的实证证据，并可区分三种潜在调控线索：个体相对数量、代谢物（化学信号）以及资源可获得性。
3. 我们以纤毛虫模式生物四膜虫（Tetrahymena）为研究对象开展微宇宙实验，以解析局域密度梯度下运动策略的可塑性，同时控制不同线索可获得性介导的混杂效应。此外，我们还探究了阿利效应（Allee effect）对运动与扩散可塑性的调控作用。
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。这一现象可能由阿利效应导致：在低种群密度下呈现负密度依赖关系，而在高种群密度下则因局域竞争普遍呈现正密度依赖关系。这种可能具备适应性的密度依赖型运动策略，大概率由化学信号介导。
5. 本研究在高度可控的实验条件下开展的工作表明，若要全面解析运动与扩散的调控机制，需同时考虑环境线索与内在种群动态。