Communities and Ecosystems
An organism, or any living thing, does not exist independently in nature. When we study ecology, we are interested in the many ways that an organism is linked to other living things and to its environent. For instance, a mouse in the forest depends on plants for its food, a hollowed out tree for its shelter, and the sun for warmth. Its fur may be a home for insects. The mouse competes with other mice for its food and shelter. Snakes and owls may depend on the mouse for food. Other organisms may feed on the mouse's waste. These are only some of the possible interactions between the mouse, other organisms, and its environment.
Let's first consider the connections between organisms. Organisms of the same kind, or species, often occur in the same area. We use the term population to describe a group of organisms of the same species that occupy a certain area. The mice in the forest, the trout in a lake, or the people in the country are different examples of populations. The place where a population lives is also called a habitat. The habitat can be a large forest or a hollowed out log. Many different populations can be found in a single habitat.
The populations in a habitat interact with each other. As described earlier, the mouse population interacts with the snake population, the tree population, and the insect population. These populations interact with each other to meet their special needs for food and shelter. A community is a group of interacting populations living in a particular place. Just as you live in a community of different kinds of people who interact with each other, living things in the natural world also exist in communities. In the previous example, all of the mice, plants, trees, insects, snakes, and owls in that particular forest form a community.
It would be difficult to study a community without considering the influence of the environmental factors such as the sun, rain, and soil. A spring with little rain could kill some of the plants that the mice depend on for food. If the numbers of mice decreased the other species in the community would also be affected. Since the environment plays such an important role in the survival of living things, ecologists study communities together with their environment. An ecosystem is a community of living things together with its environment. When you study an ecosystem you consider all interactions that occur between organisms and their environments. For example all of the plants, animals, and microorganisms living in a forest, together with the air, soil, nutrients, water, wind, and sun make up a forest ecosystem.
Ecosystems can be very small or very large, depending on the area you choose to study. An aquatic ecosystem can be as small as a puddle or as large as the Pacific Ocean. A meadow, a forest, or a mountain range are examples of different kinds and sizes of terrestrial ecosystems. Each of these ecosystems are made up of different communities and are influenced by different environmental factors. If you put together all of Earth's ecosystems, you would have the biosphere, the regions on Earth where life exists.