Colonial population dynamics of Spartina alterniflora

Smooth cordgrass, Spartina alterniflora, is a perennial grass species that forms distinctive colonies on mudflats. Such colonies can increase their size by expanding clonally to surrounding open mudflats and their number by establishing new colonies on far away from the original colonies either by sexual reproduction or rhizome fragmentation. In this work, we aimed to link colony dynamics mechanisms, lateral growth and recruitment, to reproduce the overall population dynamics of Spartina alterniflora in an integrative manner. The proposed model describes a population as a collection of age-structured colonies randomly distributed in a habitat area. By applying a mean field approach for spatial dimensions, we derive dynamics of how the expected proportion of an area occupied by these colonies would disperse over time. We derive a parameter describing the contribution of lateral growth and recruitment to population, i.e., the growth potential. This growth potential is proportional to the geometrical mean of the lateral–growth speed and recruitment rate, representing the average growth rate including these two mechanisms. Moreover, we show that lateral growth, rather than recruitment, addresses transitional dynamics of stable–age-structure developments. The ratio between colony mortality and growth potential determines the equilibrium proportion of area occupied by these colonies. The application of this model to S. alterniflora population dynamics would be feasible across a wide range of populations determined by the spatial occupations of growing colonies.