In this paper, we develop a 3D-individual-based model (IBM) to understand effect of various small-scale mechanisms in phytoplankton cells, on the cellular aggregation process. These mechanisms are: spatial interactions between cells due to their chemosensory abilities (chemotaxis), a molecular diffusion and a demographical process. The latter is considered as a branching process with a density-dependent death rate to take into account the local competition on resources. We implement the IBM and simulate various scenarios under real parameter values for phytoplankton cells. To quantify the effects of the different processes quoted above on the spatial and temporal distribution of phytoplankton, we used two spatial statistics: the Clark–Evans index and the group belonging percentage. Our simulation study highlights the role of the branching process with a weak-to-medium competition in reinforcing the aggregating structure that forms from attraction mechanisms (under suitable conditions for diffusion and attraction forces), and shows by contrast that aggregations cannot form when competition is high.

中文翻译：

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一种基于个体的 3D 模型，用于研究趋化性、竞争性和扩散性对活动浮游植物聚集的影响

在本文中，我们开发了一个基于个体的 3D 模型 (IBM)，以了解浮游植物细胞中各种小规模机制对细胞聚集过程的影响。这些机制是：由于细胞的化学感应能力（趋化性）、分子扩散和人口统计学过程，细胞之间的空间相互作用。后者被认为是具有密度依赖死亡率的分支过程，以考虑到本地资源竞争。我们实现了 IBM 并在浮游植物细胞的真实参数值下模拟了各种场景。为了量化上面引用的不同过程对浮游植物空间和时间分布的影响，我们使用了两个空间统计数据：克拉克-埃文斯指数和群体归属百分比。