Several different species of birds, including heron, flamingos, and skimmers, can all successfully feed along the coast because they get their food from waters of varying depths. this is an example of
intraspecies competition
resource partitioning
commensalism
edge effects

The correct answer is resource partitioning.  

The concept of resource partitioning is applicable in the branch of ecology. It signifies towards the procedure by which natural selection mediates competing species into distinct patterns of different niches or resource utilization.  

When the species differentiate a niche to prevent competition for food resources, it is known as resource partitioning. At certain times, the competition is among the species, known as interspecific competition, and at sometimes it is among the individuals of the similar species, that is, intraspecific competition.