Ecosystems: The World-wide Web of Life
OverviewThe world is composed of many natural ecosystems in which plants and animals interact with one another and the nonliving environment. Each species has a niche or job within the ecosystem and each is dependent on the other members of its community for survival. Students will explore the natural communities found in Shenandoah National Park and make comparisons between natural and human communities.
Following the park experience and classroom activities, the students will be able to
- Define food web and explain the transfer of energy in a sample food web;
- Determine an organism's niche in its community and describe the interdependent relationships among organisms;
- Identify at least three environmental and human influences that can impact a community and determine potential consequences;
- Explain how Shenandoah National Park protects natural communities and list three ways people can demonstrate care for the environment.
An ecosystem includes all the living organisms and the nonliving, abiotic, components of habitats. Ecosystems are often characterized by a dominant plant community, e.g., deciduous forest. All things in an ecosystem are interrelated and interdependent. Every animal either eats plants directly or depends on other species for food, which in turn depend upon plants. These relationships form food chains in which energy is transferred from one organism to another. Because most animals have multiple food sources, they are included in many possible food chains. Together, related food chains form complex food webs. The sun is the energy source that fuels all food webs.
In natural communities, each organism fills a niche or function. In general, organisms can be categorized as producers, consumers, or decomposers. Green plants are considered producers because they use photosynthesis to convert sunlight (energy) into food (sugars and starches). Herbivores are considered primary consumers because they eat plants directly, e.g., a rabbit. Carnivores are considered secondary consumers because they eat other animals, e.g., a hawk. Omnivores are consumers that eat both plants and other animals, e.g., black bear. Decomposers such as scavengers, bacteria, and fungi eat or break down dead materials to recycle nutrients back into the soil for use by plants. Decomposers are critical to complete the energy cycle in food webs within every community.
Because all organisms in a community are interdependent, if one species disappears it may have a far-reaching impact upon the other inhabitants. It may result in the loss of a food source, fewer materials for shelter, or lack of decomposition. Factors that may negatively influence communities include natural phenomena such as fire, flood, storms, and landslides and those caused by human behaviors such as pollution and habitat destruction. People can reduce or prevent damage to communities and ecosystems by practicing responsible environmental stewardship behavior.