Ecosystems Lesson

In the previous module, we learned how organisms interact with each other. In this module, we will study how organisms interact with nonliving things in their environment. For example, birds interact with the air not only when they fly but also when they inhale oxygen. We use water to cook, clean, bathe, and most importantly to drink. The nonliving things in an environment are called abiotic factors. The living things in an environment are called biotic factors. Ecology is the study of the interactions among organisms and the nonliving things in their environment. All organisms, including humans, rely on the environment in which they live in order to survive.

Watch the following presentation to learn more about biotic and abiotic factors.

Complete the following review activity to test your knowledge of biotic and abiotic factors. Drag each element into it's correct category:

Ecologists organize the interactions within an environment into five major levels: organism, population, community, ecosystem, and biosphere.

5 Major Environment Levels Image

1-Organism
2-Population
3-Community
4-Ecosystem
5-Biosphere

Ecological Levels of organization Image:

Atom (Oxygen)
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Molecule (Dioxide)
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Macromolecule (Phospholipid)
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Cell (Clara Cell)
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Tissue (Epithelial tissue)
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Organ (Lung)
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Organ System (Respiratory System)
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Population (Pride of Lions)
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Community (Lions and Zebras)
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Ecosystem (Lions, Zebras, and the Environment)
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Biosphere (Life on Earth) A single organism or individual is at the bottom of the level of organization between living things and their environment. An organism depends on its habitat, a place where an organism lives. A habitat is part of the environment that supplies food, shelter, and other things for growth and reproduction. A flower garden is a great habitat for a ladybug. The next level of organization is a population. A population is a group of individuals of the same species living in the same area at the same time. Timber wolves (Canis lupus) are predators. They live and hunt together in a group known as a pack. Timber wolves usually rely on each other for food, raising young, and defending their territory. The size of a population increases when new members are born or join the population. When members die or leave the population, the size decreases.

A community is all of the populations that live and interact in the same area. Timber wolves prey on rabbits, bison, elk, and oxen. They can live in various types of habitats. Timber wolves can be found in very cold regions such as the Artic tundra. They live in very warn climates such as a prairies, grasslands, and forests. Rabbits live in burrows. They dig holes in the soil to make their underground home out in a prairie or forest. Rabbits are herbivores. Just like timber wolves they can survive in various habitats. Timber wolves, rabbits, grass, and trees are different populations of organisms that live together to make up a community in a forest. When resources are plentiful, a population generally grows. An environmental factor that causes the population to decrease is called limiting factor. Food, water, space, and weather conditions are examples of limiting factors. The carrying capacity of an area is the largest population that it can support.

When a population reaches this level, its size remains fairly constant. When environmental conditions change, however, the carrying capacity changes as well. Changes can affect the survival of both individuals and entire species. At the carrying capacity, all of the organisms are getting enough of the resources they need. Now suppose that the environment changes in such a way that resources are reduced. For example, a drought may decrease the supply of water.

Or human construction may lead to a reduction in habitat size. Pollution may reduce the amount of healthy soil in a region. In some environments, people introduce new species of organisms. The non-native species take resources that are needed by the native species. These types of changes mean that not all of the organisms in an environment can obtain the resources they need.

In other words, the carrying capacity of the environment decreases. Some of the organisms will die, causing the population to decrease. Some species are plentiful on Earth. Others exist in only limited numbers. The success of a species is related to environmental conditions. If those conditions change, the survival of individuals as well as the entire species can be in danger. Download this document to see how Zebra Muscles affect an ecosystem.

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