Competition can occur even when resources are abundant due to

Competition can occur even when resources are abundant. In interference competition, one species can interfere with the feeding efficiency of another species, even if resources are not limiting. For example, a larger or more aggressive species might physically exclude a smaller or less aggressive species from a resource-rich area, reducing the feeding efficiency of the smaller species. This interference can result in a competitive disadvantage for the smaller species and affect its fitness, even if there is no shortage of resources.
Character displacement refers to the evolution of phenotypic differences between species to lessen competition. 

Competitive release is a phenomenon in which a species experiences reduced competition and an increase in the use of resources due to the removal or reduction of a competing species.

Resource partitioning reduces competition between species.