“No man is an island.” Every organism living in this world can not live by itself. One can not convene its needs in life on its own. Thus, there is a need for them to interrelate with other organisms that can be of assistance to them.
Interactions occur not only among the levels of organization with organisms but also between organisms but also between organisms and their external environment. Interactions between organisms and their environments are classified into the following hierarchy of levels of organization: populations, communities, ecosystems, and the biosphere. These levels of organization build on the levels of organization of individual organism.
A population consists of the individuals of a given species that occur together at one place and at one time.
Looking like homes for oversized mud wasps, the cliff swallow nests hang precariously from the face of a rock outcropping. Any rough, vertical surface will serve as a nesting site for these birds. The cliff swallows that inhabit these nests are a population of organisms.
The beautiful coral reef is home to a variety of organisms that each contributes to the array of colors evident there. The reef provides a shallow – water environment favorable to many organisms ─ schools of fish within and around the reef, eating algae and plankton that drift in the surrounding water. Together, the interacting populations of a coral reef form a vibrant, colorful marine community.
The interactions among organisms within ecosystems are varied. Individuals of the same species make up a population of organisms. Populations also interact with one another, forming communities. A community is a grouping of populations of different species living together in a particular area at a particular time.
The living organisms in a community interact not only with each other but with the nonliving substances in their environment, such as the soil, water, and air, to form an ecological system, or ecosystem.