Interspecific Competition

         

               1st Picture:   Fishing Brown Pelicans

          

               2nd Picture:   Partially Submerged Diving Brown Pelican

               3rd Picture:   Gull Atop the Pelican

               4th Picture:   Gull making away with the Pelican's catch

Interspecific competition, in ecology, is a form of competition in which individuals of different species vie for the same resource in an ecosystem (e.g. food or living space). The other form of competition is intraspecific competition, which involves organisms of the same species.

or....

Parasitism is a type of symbiotic relationship between two different organisms where one organism, the parasite, takes favor from the host, sometimes for a prolonged time. 

maybe both..............You decide.