Before explaining why competition in the intertidal zone increases species diversity, we first need to find out what competition is; how and why competition occurs.  Competition is a negative interaction among organisms contesting access to resources, such as food or space (Bertness). 

There are three types of competition: exploitative, preemptive, or active interference. 

Competition can, however, only occur where organisms share a resource and the resource is in short supply (Bertness, Gaines, Hay).  That limiting factor in the intertidal zone is obvious, space. 

            Competition for space in the intertidal zone is important because it is the one thing that can claim survival for an organism.  Food is somewhat abundant in the intertidal zone.  Some organisms still compete for food but the major limiting factor is space.