  I examine the effect of exogenous spatial heterogeneity on the coexistence of
competing species using a simple model of non-hierarchical competition for site
occupancy on a lattice. The sites on the lattice are divided into two types
representing two different habitats or spatial resources. The model features no
temporal variability, hierarchical competition, type-dependent interactions or
other features traditionally known to support more competing species than there
are resources. Nonetheless, stable coexistence of two habitat specialists and a
generalist is observed in this model for a range of parameter values. In the
spatially implicit mean field approximation of the model, such coexistence is
shown to be impossible, demonstrating that it indeed arises from the explicit
spatial structure.
