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The branch of biology that deals with the interactions between organisms and the relationships of organisms with their living and nonliving environments is ecology.

An ecologist is the person that studies ecology.

Abiotic Factors

The nonliving parts of the environment are known as abiotic factors.  They directly affect the ability of organisms to live and reproduce.  Some abiotic factors are:

1.  Light/sunlight+ Gives all energy to earth

-Amount of sunlight varies with latitude

2.  Temperature- varies with latitude and altitude

3.  water- amount of precipitation (rain, snow)

4.   Soil and Minerals – topsoil includes organic and inorganic minerals.  Dead organisms are recycles.

Humus– rich dark organic matter in soil (nutrient rich), formed from dead animal and plants.


Biotic Factors
Living Factors= plant and animals

1.  Species: organism= 1 type of living thing

2.  Population: includes all the members of a species found in a given area.  The dandelion species in your lawn is an example of a population.

3.  Community: includes all Living Organisms in a given area.  Your lawn has populations of dandelions, grasses, earthworms, and other living things.  These populations together make up a lawn community.

This diagram showhow biotic and abiotic factors combine to make a ecosystem.

4.  Ecosystem: A community (all living things) and the physical environment (air, water, soil) interacting and functioning together make up an ecosystem.  Examples of ecosystems include your lawn, a balanced aquarium, ponds, vacant lots, woods, salt marches, and forests.

5.  Biomes:  a specific condition in a specific area.

6.  Biosphere:  is the portion of the earth in which life exists because of oxygen.


Organisms have different roles within an ecosystem:

Autotrophs: (Producers/plants) These are organisms that make their own food by using CO2

Heterotrophs: (consumers/animals) These are organisms that can not make their own food.

There are different types of heterotrophs:

1.  Herbivores: Animals that feed only on Plants (ex: cattle)

2.  Carnivore:  Animals that feed only on meat. Some are predators and some are scavengers.

3.  Predators:  Attack other animals and feed on their bodies. (ex: lions)

4.  Scavengers:  Feed on dead animal bodies (ex: Hyenas and vultures)

5. Omnivores:  Feed on both animals and plants. (ex: humans and bears)

6.  Saprobes/Saprovores:  Also called decomposers.  They obtain nutrients by breaking down the remains of dead organisms and recycle nutrients back into the soil.

Symbiotic Relationships

These are relationships in which 2 different organisms live in close association with each other to benefit at least one of the two organisms.

1.  Mutualism:  Both organisms benefit. ( +,+) (Crocodile/ birds)

2. Commensalism:  One organism benefits while the other organisms is not affected.  (+,0) (Sharks/Pilot fish)

3.  Parasitism: One organism benefits (Parasite) while the other is harmed.  (+,-) (HIV/ humans)(Ticks/ dogs)


Habitat:  The part of the ecosystem where the organism lives.

Niche– The job or role the organism plays in an ecosystem.

 Food Chains

Food Chain: food energy is passed through a series of organisms. 

In this diagram the corn is serving as the producer and the mouse the vegetarian primary consumer.  The snake will eat the mouse and be a carnivorous secondary consumer, and the owl the tertiary consumer.

This food chain, starting with the seaweed and ending with the shark, also illustrates the heat energy that is extracted from each level of the food chain.

Food Webs

Food webs are food chains that are interconnected with each other making a web appearance.

In this food web you can see various food chains interconnected.  This shows several options and variety for consumers and how taking out a species can affect various organisms.  Note that decomposers are found at all levels of the of the food web recycling deceased organisms.

Pyramid of Energy

Biomass pyramids provide a plethora of information about a food chain or web in an environment.The bottom of the pyramid is always the producer with the primary then secondary consumer above it.  In each level is also vocabulary describing other characteristics about that level.  Along the right side of the pyramid in purple, are the numbers 1, 10, 100, and 1000.  These numbers represent the energy that is “lost” at each energy level.  Approximately 10% of the ingested material are used to build and repair body tissues.  The remaining 90% is lost to heat energy and unavailable chemical energy.  In the pyramid shape you can see how there is more biomass at the bottom and less as you go up the pyramid.

 Cyclical Materials

Oxygen and Carbon dioxide

This diagram illustrates the processes of cellular respiration and photosynthesis.  During photosynthesis, water and carbon dioxide with the help of sunlight are used to make carbohydrates.  Oxygen is released as a byproduct and is used by respiration to make ATP, giving off carbon dioxide.


Water Cycle

The water cycle will be explained by using the corresponding letters.  Letter A: Transpiration is the loss of water vapor from plants as a result of respiration.  Letter B: Evaporation is the change from liquid water to water vapor.  Letter C: Condensation is water vapor changing back into its liquid form.  Letter D:  Precipitation is when the liquid water falls from the sky to the surface.

Nitrogen Cycle


Nitrogenous wastes and the remains of dead organisms are converted by bacteria and decomposers into nitrates that are used by autotrophs.




 Ecological Succession

Ecological succession is the gradual replacement of one community by another.  Ecological succession eventually leads to a more stable community called a climax community.

Ecological succession occurs in several steps.  The first step on the left is the bare rock where lichens and pioneer organisms will begin to grow and break off small pieces of rock.  When these organisms die at the end of the warm season, their remnants add organic material to the rock pieces.  After years of this occurring, autotrophs like grasses will begin to grow.  Their roots will break up the rocks more and with the nutrients of past organisms and water, eventually more larger plants can grow.  As years pass the smaller plants will be replaced by larger ones forming a more stable environment.  This will occur until a climax community is created.

Below is an example of lake succession.

Letter A shows a young lake with a little sediment at the bottom and plenty of life.  As we move to Letter B, more sediment is building from dead organisms and nutrients.  Letter C shows the lake resembling more of a march or a swamp.  Letter D shows the final stage where the lake is completely filled in and terrestrial organisms cover the area.