Ecology: the study of interactions among organisms and between organisms and their environment.

How does ecology differ from evolution?

     Ecology studies interactions between organisms in a particular area (space).

     Evolution studies interactions between organisms over time.


Environmental factors in an ecosystem:


     Biotic: all the living organisms in an environment.

     Abiotic: all the non-living parts in an environment.


Biotic Factors

Abiotic Factors

Temperate Forest





What is an ecosystem?

All of the biotic and abiotic factors in an environment.

     In an ecosystem, matter and energy flow and recycle continuously. Standard B1.44

     Sunlight is the main source of energy on Earth. Energy may also come from inorganic chemical compounds.

     The flow of energy is modeled through food chains (a series of steps in which organisms transfer energy).


Examples of food chains:


Grass grasshoppers robins hawk

   1st                            2nd                       3rd                4th  


Algae    Herring         Squid         Shark

   1st           2nd                3rd               4th   

     The arrows represent the one way flow of energy.

     Each step in a food chain is called a trophic level.

     The first tropic level must always be an autotroph (producer).

     Energy is passed from autotrophs to heterotrophs (consumers) in a food chain.

     Examples of heterotrophs: herbivores, carnivores, omnivores and detritivores.

     Decomposers such as bacteria and fungus fit into the food chain at any trophic level.

     A food web links all of the food chains in an ecosystem together.



Producer: uses the suns energy to make glucose (food).
Herbivores (1st level consumer): eat plants only
Carnivores (2nd level consumer): eat animals only
Omnivores: eat both plants and animals.
Detritivore: eat detritus (decaying material)
Decomposer: convert dead material to detritus AND recycle nutrients in food webs.


Ecological pyramids:

Energy pyramid Standard B1.37

     90% of the energy is lost as heat to the environment at each trophic level.

     10% of the energy is passed on to the next trophic level.

Biomass pyramid

     Biomass is the total amount of living tissue.

     Represents the amount of potential food (in grams) available for each trophic level.





Pyramid of Numbers

     Based on the number of individual organisms at each trophic level.


NOTE: Each pyramid has the most at the first trophic level and the least at the top trophic level.