An organism is an individual form of life, such as a bacterium, fungus, plant, or animal, composed of a single cell or a complex of cells in which organs work together to carry out the various processes of life.

And the hippopotamus is an organism

Ecology deals with the relations of organisms to one another and to their physical surroundings.

In an absolute way, every aspect of our life belongs in ecology.

See Environmental Enlightenment #220, Ecosystems, on the relations of organisms to each other and to their physical surroundings.

Ecological Balance is a term that describes how ecosystems are organized in a state of stability where species coexist with other species and with their environment. For example, predators keep mice under control, insects pollinate flowers, and worms decompose leaf matter. All species are important and help keep the ecosystem balanced. (Acknowledgment: Study.com)

Healthy ecosystems and environments are necessary to the survival of humans and other organisms.

Sustainability is how ecosystems remain diverse and productive.

A sustainable plan, program, project or system is one that conserves ecological balance by avoiding depletion of natural resources.

Long-lived and healthy wetlands and forests are examples of sustainable systems.