A computational model of metapopulation dynamics and organism-mediated nutrient flow

Sammanfattning: The aim of this project was to assess, using in-silico experiments, how different life history char-acteristics, such as age at maturity and dispersal ability of individuals, influence the dynamics of a metapopulation. To achieve this, a novel model of a spatially explicit metapopulation, with organ-ism-mediated nutrient flow between fragmented habitat patches, was implemented by means of computer simulations. The habitat is a two-dimensional grid plane. Each grid cell is a patch that can hold a population and nutrients. Nutrient flow is exclusively dependent on the migration of individuals between patches. The species is hermaphroditic and facultatively self-fertilising. Each individual requires two resources, nutrients and energy, for growth, migration, survival and repro-duction. In the model, nutrients are acquired from the habitat, and they are, in part, used to produce energy. Time is modelled in discrete steps corresponding to the age of individuals. Within individual patches, the model assumes nutrients to be homogeneous, and mating to be random. Generations are overlapping. Unlike most population dynamics models, the carrying capacity and intrinsic growth rate are not explicitly defined in the current model. Instead, they are emergent model properties, influenced jointly by multiple model parameters. We assessed the model out-comes for different values of two parameters, namely, age at sexual maturity and the probability of migrating to a neighbouring patch. Initially, nutrients were distributed homogeneously across all patches, while only the four central patches were populated. We found complex metapopulation dynamics with local extinctions and recolonisations, wherein population size grew in a logistic fashion during recolonisation. A higher maturity age tended to result in a higher initial growth rate and higher carrying capacity, whereas a higher probability of migration tended to result in a higher initial growth rate and lower carrying capacity.