The significance of spatio-temporal neighbourhood on plant competition for light and space

Cellular automata models are increasingly being used to examine plant competition and vegetation dynamics. Though these models have provided many theoretical and practical insights, they are inevitably limited by the hierarchical rules that determine the outcome of interactions between plants. Most frequently, the models consider only close-range interactions (nearest neighbour) at a fixed scale and neglect to address the effect of initial plant densities and unoccupied space. This paper explores the concept of interactions between individuals through a ‘surface’—representing a leaf system—which overlaps with the space occupied by surrounding individuals. Simulations demonstrate that the size of this surface has a considerable effect on the outcome of competition. In particular, a more extensive surface than nearest neighbour confers greater competitive ability for light (even though the total resource available to any individual is held fixed). The implications of overlap are examined through simulating the interference between two species: the ‘resourcer’, which has superior resource capture, and the ‘coloniser’, which has superior dispersal. The greater competitive ability conferred by a more extensive surface in the resourcer led to reduction, sometimes to extinction, of the coloniser. This trend could be countered so that co-existence was encouraged by (a) starting with a low occupancy that allowed the coloniser to form aggregates and (b) restricting the competitor with a trade-off between high resource capture and high minimum resource required for survival. It is proposed that the approach using overlapping surfaces can be applied generically in spatial modelling as a means of introducing physiological parameters.