A model interaction-diffusion equation for population density originally analyzed
through terms of third-order in its supercritical parameter range is extended through
terms of fifth-order to examine the behavior in its subcritical regime. It is shown that
under the proper conditions the two subcritical cases behave in exactly the same
manner as the two supercritical ones unlike the outcome for the truncated
system. Further, there also exists a region of metastability allowing for the
possibility of population outbreaks. These results are then used to offer an
explanation for the occurrence of isolated vegetative patches and sparse
homogeneous distributions in the relevant ecological parameter range where there is
subcriticality for a plant-groundwater model system, as opposed to periodic
patterns and dense homogeneous distributions occurring in its supercritical
regime.