NICHE SPACE, MULTIGRAPHS, AND THE HELLY CONDITION

Niche overlap graphs (frequently called competition graphs) have becom e familiar models of food webs. A simple refinement of these models to multigraphs and pseudographs suggests that several properties, relate d to the combinatorial ''Helly condition'' but not previously investig ated in this context, may be more relevant to questions concerning foo d webs and niche spaces than are the traditionally considered properti es.