A simulation study on how the resource competition and anti-predator cooperation impact the motile-phytoplankton groups' formation under predation stress

Authored by Ilhem Bouderbala, Saadi Nadjia El, Alassane Bah, Pierre Auger

Date Published: 2019

DOI: 10.1016/j.ecolmodel.2018.10.019

Sponsors: No sponsors listed

Platforms: GAMA

Model Documentation: ODD Mathematical description

Model Code URLs: Model code not found

Abstract

The phytoplankton's spatial aggregation is a very important phenomenon that can give responses to many questions such as the passage from the unicellularity to the multicellularity. In this work, we are interested by predator-induced aggregations in motile phytoplankton. Our aim is to bring, through a simulation study, some explanations on how these groups form and analyze the simultaneous effect of both resource competition and anti-predation cooperation on the groups' formation process. For this purpose, we developed a 3D individual based model (IBM) that takes into account small-scale biological processes for the phytoplankton cells that are: (1) motion, described by a stochastic differential equation in which the drift term is density-dependent to take into account the attraction mechanism between cells due to their chemosensory abilities and the dispersal term representing the diffusion of cells in water, (2) a density-dependent birth-death process to describe the demographical process in phytoplankton cells. In the latter, division and death rates were considered density-dependent to include a local competition for resources that slows up the cell's division and a local cooperation in phytoplankton that reduces the cell's predation death. We implemented the IBM and considered several scenarios that combine three different levels of resource competition with three different intensities of cooperation. The different scenarios were tested using real parameter values for phytoplankton. The simulation of the IBM showed that phytoplankton cells form aggregations via the ``coming together{''} mechanism driven by the cell's motion process in which, the attraction mechanism is enhanced by the cooperation behavior (the latter is a response to the predation stress). After that, groups grow through the ``remaining together{''} mechanism which is a consequence of the division-death process and also the attraction mechanism which prevents the daughter cells from leaving the group after division. Also, the simulation of the different scenarios highlights the role of cooperation in the formation of aggregates and shows that although resource competition impairs the aggregation process and the group size, cooperation plays an important role in sustaining the aggregating process and when it is strong, the induced aggregation process is so successful that it completely prevents cells being grazed; and both group and population sizes are maintained at a good level.

Tags

Individual-based model Resource competition Risk population Model Aggregation Group-size Life-cycle Avoidance Chemosensory responses Dinoflagellate Predator-induced aggregation Chemosensory ability Density-dependent birth-death process Anti-predation cooperation Scenedesmus