Regents Prep: Living Environment: Organization:
Population Diversity

Ecological Organization
Ecology is the study of the interactions of living things with each other and their physical environment.   The living things on earth may be organized into four different levels of ecological organization.    These levels of organization are indicated in the table below.

Levels of Ecological Organization

1.  population all the members of one species in an area
2.  community all the members of the different interacting species in an area
3.  ecosystem all the members of a community plus the abiotic (physical) factors influencing them
4.  biosphere entire region of the earth where living things may be found

A Representation of A Community

This is a community of many different organisms which could exist on milkweed.  The community contains many organisms of different species in one location.

A Pond Ecosystem

This is a pond ecosystem.   There are many organisms of different species in this location interacting with the air, water, and land components of this environment.

Nutritional Interactions
All ecosystems must have three basic kinds of nutritional interactions in order to be stable and self-sustaining.   These nutritional interactions involve producers, consumers, and decomposers.   

A producer organism is one that is capable of trapping the Sun's energy to make glucose sugar in the process of photosynthesis.   Plants and algae are examples of producer organisms.   Sometimes producer organisms are called autotrophs.   Consumer organisms depend upon and eat other organisms for their food.    Sometimes consumer organisms are called heterotrophs.   Many different categories of consumer organisms exist.   A herbivore eats primarily plant material, while a carnivore eats primarily other animals.  An omnivore is a consumer that eats both plant and animal material.   Humans are an example of an omnivore.   A decomposer is a special category of consumer organism.   Decomposers break down dead organic matter and change it to simpler nutrients which can be recycled in the ecosystem.   

Circle of Life

In order for an ecosystem to sustain life, several conditions must be met.

       Some Conditions for a Stable Ecosystem

  • A constant source of energy and a living system capable of incorporating this energy into organic molecules. (This means plants and/or algae are needed to convert solar energy to the energy of sugars by the process of photosynthesis.)
  • A cycling of materials between organisms and their environment.  (Some material cycles include oxygen, carbon dioxide, water, and nitrogen.)  Decomposers, such as bacteria of decay and some fungi are needed in every ecosystem to return and recycle necessary materials to the environment.

The greater the number of different populations that interact within an ecosystem, the more stable and self-sustaining the ecosystem becomes. The number of different populations within an ecosystem is sometimes referred to as biodiversity. These interactions contribute to the overall maintenance of the ecosystem.

Niche Concept
occurs when two different species or organism living in the same environment or habitat use the same limited resources such as food, water, space, light, oxygen, or minerals. A resource which restricts the growth of a population is sometimes called a limiting factor. The more similar the requirements of the organisms involved, the more intense their competition will become. If two different species compete for the same food source, reproductive site, water, or other limiting factor, one species may be eliminated. This establishes one species per niche in an ecosystem. A niche refers to an organismís role, especially its feeding role, in a community. This allows different species to coexist and helps to contribute to the overall stability of the ecosystem.

Niche Concept

Three different species of a kind of bird called a warbler are coexisting in this tree, even though the eat the same kind of food.   These birds are feeding in different levels of this tree.   In this way, these birds have evolved to occupy different niches.


Created by James M. Buckley, Jr.
Copyright © 1999-2003 Oswego City School District Regents Exam Prep Center
RegentsPrep and StudyZone are FREE educational resources.