What is an Ecosystem

Not even a lone wolf is a “lone wolf.” Every organism on the planet is dependent on others to live. Through ecology, the study of ecosystems, we can begin to understand how we rely on the natural world. Ecosystems can come in many sizes, from a large forest to a tiny puddle, and through the study of ecosystems we begin to understand how living organisms in a certain place interact with each other (Who eats what? Who will compete with whom and for what resources?). We can also understand how these living things interact with the nonliving parts of their environment (like the soil, the temperature, the air, and the water).

Interactions between wildlife and their environment provide us with important natural services. Ecosystems large and small are responsible for breathable air, fresh water, protection from natural disasters, fertile soil, and of course food! By understanding ecosystems we can see how energy from the sun flows through the food web, and how the cycle of life, death, and decay allows nutrients to be reused. Only when our ecosystems are intact can the natural world continue to seamlessly do the hard work of sustaining life on planet Earth.

TROPHIC LEVELS: An organism’s position in the food web, and how far away it is from the original source of energy (the sun), starting with producers and typically ending with apex predators.

WHO EATS WHAT: Producers make their own food from solar energy. Herbivores eat only plants. Carnivores eat only other animals. Omnivores eat both plants and animals. Decomposers eat waste and dead organisms.

FOOD WEB: The mapping of the flow of energy. Who eats what and who gets energy from whom. Arrows point to who is enjoying a tasty meal, which is the direction energy is moving.

The Flow of Energy

Matter—which makes up our bodies and everything else—can never be destroyed or created. It cycles, transforms, and is constantly reused. Energy works differently. New solar energy constantly flows into our planet’s ecosystems and is then used up and lost forever in the form of heat. Living things don’t just eat each other to get the vital nutrients they need to grow strong. Food also is about gaining energy. Almost all of the energy for life originally comes from the sun. Plants and algae (also known as producers) can turn sunlight into sugar through a process called photosynthesis. Sugar is a form of chemical energy that is stored. During the complicated process of cells doing work, energy is released and lost as heat. Plants use around 90 percent of the original stored energy that they make. (Living takes work!) Only about 10 percent of the original sunlight energy remains stored as sugar. When a plant is eaten, this stored sugar energy begins its own journey through the food web.

Producers are at the bottom of a food web and hold the most stored energy. As you move up the food web—from producers to primary and secondary consumers and so on—more of that original energy is used up and less energy as a percentage of food mass is passed along. That means that an apex predator, which is at the top of a food web, needs to eat much more than a primary consumer to get the same amount of energy.