Geometry for a penguin-albatross rookery.

We introduce a simple ecological model describing the spatial organization of two interacting populations whose individuals are indifferent to conspecifics and avoid the proximity to heterospecifics. At small population densities Φ a nontrivial structure is observed where clusters of individuals arrange into a rhomboidal bipartite network with an average degree of 4. For Φ → 0 the length scale, order parameter, and susceptibility of the network exhibit power-law divergences compatible with hyperscaling, suggesting the existence of a zero-density nontrivial critical point. At larger densities a critical threshold Φ(c) is identified above which the evolution toward a partially ordered configuration is prevented and the system becomes jammed in a fully mixed state.