All animals depend on plants. Some animals eat plants for food. Other animals eat animals that eat the plants. An organism's patterns of behavior are related to the nature of that organism's environment, including the kinds numbers of other organisms present, the availability of food and resources, and the physical characteristics of the environment. When the environment changes, some plants and animals survive and reproduce, and others die or move to new locations.
All organisms cause changes in the environment where they live.
Some of these changes are detrimental to the organism or other organisms, whereas other are beneficial. Humans depend on their natural and constructed environments. Humans change environments in ways that can be either beneficial or detrimental for themselves and other organisms. 5-8 Populations and Ecosystems A population consist of all individuals of a species that occur together at a given place and time. All populations living together and the physical factors with which they interact compose an ecosystem.