Students know ecosystems can be characterized by their living and nonliving components.

This standard introduces the concept of an ecosystem. The California Science Framework (page 61) uses the terms biotic and abiotic in referring to the living and nonliving components that distinguish ecosystems from each other.

Whenever we analyze something in our world in terms of systems, we encounter a phenomenon called “nested systems” or “systems within systems within systems.” A human being can be considered a system that has parts that define it. Some of these parts are known as the circulatory system, the nervous system, and the digestive system. Each of these body systems is made of parts. The circulatory system is made of the heart, veins, arteries, and capillaries. The heart, for example, can be considered as a system that is made of muscle and nerve cells. Thus, we have systems within systems within systems.

Ecosystems also have this characteristic of systems within systems. The California Sierra Nevada mountains can be considered a very large ecosystem that stretches most of the length of the state. Yosemite National Park is an ecosystem within the Sierra Nevadas. Mariposa Grove is an ecosystem within Yosemite that is dominated by giant Sequoia Redwood trees. A decaying fallen redwood tree is an ecosystem within Mariposa Grove. Each of these ecosystems within ecosystems within ecosystems is defined by its physical setting and the organisms that live there.

Ecosystems vary in size from very large to very small. You probably do not want to think too much about it, but your belly button is an ecosystem for the organisms that live there. When scientists analyze Earth’s planetary biodiversity (all the organisms that live here), they are considering Earth as an ecosystem. Textbooks often describe biomes as one of the largest classifications of ecosystems. Biomes include Earth’s grasslands, temperate forest, rainforests, tundra, and ocean shorelines.

In general, physical conditions, such as temperature and moisture, set the parameters determining which organisms can live in a particular ecosystem. These conditions help determine the nature of the producers (generally plants) in the ecosystem which then sets the stage for the herbivores, carnivores, and decomposers. However, we should not over-emphasize the role of the nonliving components. Organisms interact with the biotic and abiotic factors, and can significantly change ecosystems.