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Ecology
ecology : the
study of the
interactions of
living organisms
with one another
and with their
environment
Populations
A population consists of all the individuals of a
species that live together in one place at one
time.
All the E. coli in your gut
All the people on earth
The two goldfish in your bowl
A population’s future survival is
determined by its size,
density, and dispersion.
How are size,
density, and
dispersion factors
in the success of
ants?
Patterns of dispersion
How can each pattern affect the success of a
population?
Carrying capacity
the population size of the species that the environment
can sustain indefinitely, given the food, habitat,
water, and other necessities available in the
environment.
Why will the human population growth curve eventually change from an exponential
curve to a logistic curve?
Density dependent vs density
independent factors
• Density dependent: resources that are depleted
such as food and water
• Density independent: environmental factors such
as weather and climate
Are predators density dependent or density
independent factors?
The Hardy-Weinberg Principle
• The frequencies of alleles and genotypes
remain constant in populations in which
evolutionary forces are absent
• Evolutionary forces include: mutation,
migration, non-random mating, genetic drift,
and environmental changes.
Will the population in your goldfish bowl
evolve? Why or why not?
Ecosystems
• A community is a group
of species that lives
together in the same
place
• An ecosystem is the
community plus the
non-living environment
Ecosystems change through the
process of succession
Primary succession occurs in a newly formed habitat
Example: After a
glacier recedes,
the newly
exposed land has
few nutrients
Pioneer plants (lichens &
mosses) begin to grow.
Then grasses and shrubs
take over. They add
nitrogen to the soil.
As the amount of soil
increases, trees become
plentiful and create
shade, eliminating the
short plants.
Can you think of other examples of newly formed habitats?
Secondary succession occurs in habitats that
previously supported growth
Example: A field that has been cleared of forest.
No two successions are alike. They depend on initial
conditions, chance, weather, etc.
How is the soil different in primary and secondary successions?
Energy moves through ecosystems
• Energy cannot be created or destroyed. It can only be
changed from one form to another.
• All of the energy on the earth originates from the sun.
• The radiant energy from the sun is stored as chemical
energy in plants through the process of photosynthesis.
Energy Flow in Ecosystems
The sun:
the source
of all the
energy on
the earth
Producers capture
and store energy.
Examples: plants,
cyanobacteria,
algae.
Also known as
autotrophs
Consumers eat (consume)
other plants and animals to
obtain energy.
Examples: everything except
for producers.
Also known as heterotrophs.
Trophic Levels
A Trophic level is a
step in a food chain or
food pyramid
• “Troph-” means “food”
or “nutrition.”
• “auto-” means “self”
• “hetero” means
“different” or “other”
A food chain is a single
path of energy in an
ecosystem
Food Webs
• Energy doesn’t
flow in simple
straight paths
• Animals often
feed at
different
trophic levels
Why does a food web
make a more stable
ecosystem than a food
chain?
Energy pyramid
trophic levels
Carnivores
eat animals
Omnivores
eat plants
and animals
Herbivores
eat plants
Why are the lower levels more diverse and more stable?
Wait! What about the “The circle of life?”
worms
bacteria
• Decomposers, also called detrivores,
obtain their energy from waste and
dead bodies at all trophic levels.
• This releases the energy back into the
environment to be used by others.
fungus
Energy transfer
• The chemical energy
in food is
transformed by an
organism into kinetic
energy (movement)
and heat energy,
which is lost to the
environment.
• The energy stored in
a trophic level is one
tenth of that stored
in the lower level.
Community Interactions
• Some interactions among
species are the result of a
long evolutionary history in
which many of the
participants adjust to one
another over time.
• Back-and-forth evolutionary
adjustments between
interacting members of an
ecosystem are called
Coevolution
Symbiosis: two or more species living
in a close, long term association
Predation
• One organism killing another for food
predator
prey
parasitism
• One organisms feeds on and harms another
A tick feeding on a dog
Mutualism
• Both organisms benefit
Aphids secrete honeydew for the ants
Ants protect the aphids
commensalism
• One organism benefits and the other is not
affected.
The sea anemone
protects Nemo, the
clownfish
The anemone does
not seem to benefit
Biogeochemical
Cycles
Or, Nature Doesn’t Throw Anything Away
The Carbon Cycle
• All organic life consists of
carbon, hydrogen, oxygen,
nitrogen, and sulfur in large
quantities
• Other inorganic molecules are
also necessary
• They pass through the nonliving environment through the
living environment, and back to
the non-living environment.
All organic molecules have carbon
• Is there carbon in sugar?
• Is there carbon in CO2 ?
Matter cannot be created or destroyed
• The Earth has only a fixed amount of carbon.
• Carbon is the ultimate form of recycling.
Carbon enters living organisms through
plants and other autotrophs
• How do plants use carbon?
– Photosynthesis –
• Takes CO2 from atmosphere and combine with water
Heterotrophs Eat the Plants
• Heterotrophs are non-photosynthetic
organisms
– Cannot create their own food
– Break down sugar and starches through cellular
respiration
– What are the products of cellular respiration?
– Energy
– H2O
– CO2
– CO2 goes back to the atmosphere to use again.
What Eats Animals at the top of the
food chain?
• Decomposers are involved in the carbon cycle
– Break down organic materials
• Dead plants and animals
• Feces
– Produces gasses
• CO2 and Methane
Carbon atoms may
return to the pool of
carbon dioxide in
the air and water in
three ways.
1. Respiration.
2. Combustion.
3. Erosion.
p. 352
The Nitrogen Cycle
• What is Nitrogen?
– An element just like
carbon
– Nitrogen is a part of
PROTEINS
– Nitrogen is a part of DNA
• Where is Nitrogen?
– 97 of the atomosphere
– Most plants and animals
cannot use it in its
diatomic state (N2)
– It must be fixed (put in a
biologically useful
compound)
Nitrogen Cycle
1. Nitrogen fixing bacteria in
plant roots convert it to
ammonia
2. Decomposers also convert
waste into ammonia
3. Then bacteria convert the
ammonia to nitrates
4. Plants absorb the nitrates
through the roots
Nitrogen Cycle
5. Herbivores eat plants
and convert many of
the amino acids into
new proteins
Omnivores eat both
plants and animals and
convert into new
proteins.
The final step
6. Nitrogen atoms are
returned to the soil in
feces and dead animals
Once in the soil the
process happens again!
Nitrogen Cycle: Bacteria carry out many of the important steps in
the nitrogen cycle, including the conversion of atmospheric nitrogen
into a usable form, ammonia. p. 353
The Water Cycle
clouds
Condensation
Precipitation
Water vapor
Transpiration
Runoff
Evaporation
ocean
lake
groundwater
Evaporation
Percolation
into soil
BIOM
ES
60 N
30 N
E
30 S
60 S
A Biome is a major biological community that occurs over a large area.
Biomes are influenced by latitude, temperature, rainfall, soil, wind, and elevation
Tropical Rainforest
Latitude:
Temperature:
Rainfall:
Importance:
Tropical Savanna
Latitude:
Temperature:
Rainfall:
Importance:
Taiga
Latitude:
Temperature:
Rainfall:
Importance:
Tundra
latitude:
Temperature:
Rainfall:
Importance:
Desert
Latitude:
Temperature:
Rainfall:
Importance:
Temperate Grassland
Latitude:
Temperature:
Rainfall:
Importance:
Temperate Forest
Latitude:
Temperature:
Rainfall:
Importance:
Deciduous
Pine
Aquatic Biomes
Freshwater
Limnetic
Profundal
Life Zones
Littoral
Marine