Individual-based modelling of ecological systems and social aggregations




Charnell, Moshi Arthur

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This thesis gives a general model formulation of discrete time individual-based models and two specific individual-based models for gregarious behaviour. A spatially explicit individual-based model for a predator, prey and plant ecosystem is the first specific model considered. The movement of the individuals is solely based on nearest-neighbour attraction/repulsion and reproduction is asexual. The second specific model considered is a spatially explicit individual-based model for schooling behaviour. The movement of the individuals is based on the physics of fluids and their reactions (repel/comfort/attract) are solely based on directional light intensities. In the ecosystem model emergent spatial organization of the individuals into clusters or groups is present even though all the individuals (predators and prey) are intra-specifically repelled by each other. The model ecosystem was used to determine whether an intra-specific attraction among the prey could increase their individual fitness. The attraction mechanism considered is such that when a prey is not affected by a predator or a plant then this prey is attracted to its nearest-neighbour prey. Under the assumptions of the parametrized model ecosystem, this mechanism seems highly selective on the individual level. The schooling model assumes that the individuals have absolutely no spatial reasoning and cannot discern other individuals as individuals. In particular, the individuals school without the capacity to match the velocities or orientations of other individuals. Individuals have the ability to perceive their environment using directional photo-sensors and adjust the direction of their acceleration in response to the values of these photo-sensors. This result should fundamentally change the way social aggregations are modeled. The main objective of this thesis is to formalize mathematically individual-based models with the intention that they become more prevalent in the scientific inquiry into assessing evolutionary aspects of social behaviour.



Individual-based, Modelling, Ecology, Schooling, Tritrophic