Major Understandings

1.1a Populations can be categorized by the function they serve. Food webs identify the

relationships among producers, consumers, and decomposers carrying out either

autotropic or heterotropic nutrition.

1.1b An ecosystem is shaped by the nonliving environment as well as its interacting

species. The world contains a wide diversity of physical conditions, which creates a

variety of environments.

1.1c In all environments, organisms compete for vital resources. The linked and changing interactions of populations and the environment compose the total ecosystem.

1.1d The interdependence of organisms in an established ecosystem often results in

approximate stability over hundreds and thousands of years. For example, as one population increases, it is held in check by one or more environmental factors or another


1.1e Ecosystems, like many other complex systems, tend to show cyclic changes around

a state of approximate equilibrium.

1.1f Every population is linked, directly or indirectly, with many others in an ecosystem. Disruptions in the numbers and types of species and environmental changes can

upset ecosystem stability.