Introduction to Ecology

What Is Ecology?


Ecology comes from the Greek words oikos (house or place where one lives) and logos (the study of). It is the study of the Earth and its inhabitants.

Specifically, Ecology is defined as the study of the interactions among organisms, and their interaction with the nonliving parts of their environment. All parts of the Earth are interdependent upon each other. To study this, ecologists collect information about organisms and their environment and look for ways to explain the patterns that they measure.


Levels of Organization in Ecology

Ecology examines the abiotic and biotic parts of the biosphere.  The biosphere is the portion of the earth that can support life, from the soil, to the oceans, and even the atmosphere where birds fly.

  1. Abiotic factors are the nonliving physical conditions or resources that affect living things in the biosphere. These include soil, water, air (oxygen, carbon dioxide), temperature, and sunlight.
  2. Biotic factors are the living things in the biosphere. These include bacteria, other microorganisms, fungi, algae, plants and animals.


Stop and Think: Which of the following things pictured in the scene above are abiotic? Which are biotic? (answer: abiotic-soil, air, sunbeams, stream; biotic-animals and plants, which includes trees)

The biosphere is built of many other levels, the first of which is all of the Earth’s ecosystems. Examine the diagram below that illustrates the Levels of Organization in Ecology. Study the table below to learn more about each level. You will be expected to know the definitions and examples for each, as well as the order of the levels.


Level Definition Example
Biosphere The portion of the Earth and atmosphere where life exists The air, water, and terrestrial areas where life can exist; biome plus atmosphere
Ecosystem The living things in an area, along with their environment The seashore including all the animals, plants, algae as well as the wind, minerals/rocks, water and weather
Community All of the populations that live in a defined area All the animals, plants, fungi and bacteria that live together in a forest
Population A group of individuals in the same species within a defined area Squirrels in your neighborhood or algae growing in a test tube
Organism/ Species A living thing, unicellular or multicellular that lives in the same location and can interbreed with others of its kind Blue whale, mushroom, pine tree

The Biome

Biomes are broad areas composed of ecosystems or groups of ecosystems. They are characterized by specific vegetation (plant life) and climate (precipitation and temperature). They would most likely fall between ecosystem and biosphere on the table above.

Two major groups of biomes exist:

  1. Aquatic biomes – based on water, such as oceans or freshwater lakes
  2. Terrestrial biomes – based on land, such as tropical rainforests, or deserts

The abiotic factors in a biome (temperature and precipitation) will define what sort of plant life can exist in an area. This in turn, determines the habitats for other living things.

Aquatic biomes are divided into two major groups:

  1. Marine biomes – bodies of seawater (more than 1% salt) such as oceans, coral reefs and estuaries (where ocean meets streams/rivers)
  2. Freshwater biomes – bodies of water that contain less than 1% salt, such as ponds, lakes, streams, rivers and wetlands (standing water)


Ecologists study the biosphere because all organisms must share the biosphere and ecologists must understand how they interact individually and collectively.

  • An ecologist may want to examine how different components interact within a controlled environment so laboratory experiments are set up.
  • Many ecological phenomena are difficult to study because the environment is always changing, sometimes unexpectedly, and ecologists may have a hard time determining which factor caused a specific observation.
  • Ecologists make models to represent environments or organisms to examine or demonstrate a specific characteristic.
  • Sometimes mathematical formulas are developed to interpret results and predict outcomes. (source)


(source apart form ecologist section)