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Chapter 3: What is Ecology?
Can you live independent of other living things? Why or why not?
A. Ecology: study of interactions between organisms and their
environment
 “Eco” = environment
 Consists of:
o Abiotic Factors: non-living factors (sunlight,
temperature, oxygen, carbon dioxide, water, pH)
o Biotic Factors: living factors (other organisms – plants,
animals, predators, prey)
B. Levels of Ecology
Smallest 1. Organism: a single living thing (ex. One plant, one human, one
bacterium)
2. Population: a group of organisms of the same species (ex.
Many deer, many oak trees)
 Hint: have a specific name
 Compete for resources, food, water
3. Community: many populations in one area (many deer, many
rabbits, many shrubs, many flowers, many wolves)
 All living organisms in an area
 A change in one populations causes a change in another
4. Ecosystem: all living (biotic) and non-living factors (abiotic)
in one area
 Community + temperature, water, sunlight, soil, etc.
Largest
5. Biosphere: any part of Earth where life exists
 Bio = life
sphere = Earth/world
C. Energy Flow through and Ecosystem
******Sun is the main source of energy for all of life on Earth.
 Energy is passed from organism to organism along the
food chain or food web
 Energy decreases because each organism at each level
uses energy itself for homeostasis. The remaining
energy is then passed to the organism that consumes it.
 Energy is lost in the form of heat when maintaining
homeostasis. It cannot be recycled.
 The material or matter that is left from the decaying
organism is recycled. Matter cannot be created or
destroyed, just transformed
1. Producer/Autotroph:
 Organisms that can make their own food
 Use the energy from the sun to perform photosynthesis
 Ex. Plants, trees, grass, flowers, algae
2. Consumer/Heterotroph:
 Any living thing that cannot make its own food, but must go
out and consume other organisms
 Types:
a. Herbivore: feeds only on autotrophs/producers
 Plant eaters, often prey for other animals
 Ex. Deer, rabbits, insects, fish,
b. Carnivore: feed on heterotrophs, herbivores and other
carnivores
 Meat eaters or predators
 Ex. Lions, bears, sharks,
c. Omnivore: feeds on both heterotrophs (animals) and
autotrophs (plant material)
 Only found in the food web
 Ex. Birds, humans, bears
d. Scavengers: feed on the remains of dead organisms
 Ex. Seagulls, hyenas, crows, buzzards
e. Decomposers: break down the remains of dead
organisms and return nutrients/energy to the ground
 Must be present in order for the ecosystem
to be balanced
 Ex. Fungus, mushrooms, bacteria
3. Feeding Relationships
a. Food Chain: a series of steps that show the
transfer of energy
 Arrows point in the direction of where energy is
being passed to
 Only shows only possible feeding relationship
Autotroph/producer
Herbivore
Carnivore
Decomposer
Heterotrophs
b. Food Web: links several food chains
 Shows multiple feeding relationships
 Omnivores present
c. Food Pyramid: shows how much energy is available
at each level
 Energy is lost as heat when organisms use the
energy they obtained from the previous level
for their own metabolism/homeostasis
 There has to be more organisms at the lower
levels to ensure that there is enough food for
the next level.
D. Cycles in Nature
 Unlike energy that is lost in nature, matter (water, oxygen,
carbon, nitrogen) are recycled
 Matter is transformed and becomes part of other organisms and
is in the food they consume
1. Water Cycle
a. Evaporation: liquid changes to gas
b. Transpiration: the water released from plants is
evaporated
c. Respiration: water vapor released during breathing
d. Precipitation: water returns to the earth in the
form of rain, snow, hail, sleet
e. Runoff, Seepage, Root Uptake: reenters organisms
(autotrophs) through the ground
2. The Carbon Cycle (C):
a. Photosynthesis (plants) and respiration (animals) take
in and release carbon dioxide (CO2)
b. Carbon is passed through organisms as they are
eaten
c. Erosion and volcanic activity release carbon
d. Decomposition and decay release carbon stored in
the dead organisms back to the environment
e. Burning fossil fuels releases carbon (increases the
greenhouse effect)
3. Nitrogen Cycle (N):
 Nitrogen makes up protein (muscle and plant tissue)
 Released from the body in the form of sweat and urine
 Nitrogen fixation: bacteria in the soil convert nitrogen to
a useable form for plants
 Denitrification: when organisms decompose bacteria
convert nitrogen from the tissue into nitrogen gas