Section 1: Organisms and Their Relationships
Ecology
◦ the study of the
interactions between
organisms and the
biotic and abiotic
components of their
environment

The biosphere is the portion of Earth that
supports life.
◦ “bio” means life
◦ “sphere” refers to the shape of our planet that
resembles a ball
 “The ball of life”
◦ Includes our atmosphere, landmasses, bodies of
freshwater and saltwater, and locations below the
Earth’s surface that supports life.

Biotic Factors
◦ All of the LIVING things in
an organism’s
environment.

Abiotic Factors
◦ All of the NONLIVING
things in an organism’s
environment
 Includes temperature, air
currents, sunlight, rainfall,
soil type and available
nutrients

No single organism is isolated!!
◦ The interconnectedness or interdependence of all
organisms is central to the study of ecology
◦ The survival of organisms depends on their
interactions with their surrounding environment
 Ex: Humans cannot live without the plants that
produce food and oxygen

Biosphere: the broadest and most inclusive
level of organization
◦ The Earth and its atmosphere make up our
biosphere
 Extends from 8 to 10 km (5-6 miles) above the Earth’s
surface to the deepest parts of the ocean

The biosphere is comprised of smaller units
called ecosystems
◦ Includes all of the organisms and the abiotic
environment found in a specific place
 Ex: Pond Ecosystem
 Abiotic components: water temperature, amount of
dissolved oxygen and carbon dioxide, the pH level
 Biotic components: insects, fish, algae, aquatic plants,
turtles
 Some ecosystems can be considered the habitat of an
organism.
Chapter 18

Niche
◦ the role an organism plays in its environment
◦ Includes:
 Range of conditions the organism can tolerate
 Methods by which it obtains resources
 Interactions with its environment such as
reproduction
•
•
Community
• all of the interacting organisms living in an area
– Ex: All of the fish, turtles, insects, plants and
algae make up the community of a pond
Competition occurs when more than one
organism uses a resource at the same
time.
– Ex: Lions and hyenas compete for the same
food sources.
•
Predation is the act of one organism
consuming another for food.
Chapter 18
•
Most species survive because of relationships
called symbiosis
– Mutualism:
• Both organisms benefit
– Ex: The Egyptian plover takes insects from the backs of
buffaloes, giraffes and rhinos
•
Commensalism:
– One benefits; the other is not affected
• Ex: Sea anemone and the clown fish.
•
Parasitism:
– One benefits at the expense of the other
• Ex: Deer tick and mammal
Visual Concept
Section 2: Flow of Energy in an Ecosystem

Autotrophs:
◦
◦
◦
◦
primary producers
make their own food
Use energy from sunlight or inorganic substances
Foundation of all ecosystems
 they make energy available for all of the other
organisms
 Ex: Plants

Heterotrophs:
◦ get energy by consuming
other organisms
◦ Called “consumers”
◦ Herbivores
 eat only plants
◦ Carnivores
 eat others

Heterotrophs Cont:
◦ Omnivores
 eat both plants and animals
◦ Detrivores
 eat dead/decaying material
◦ Decomposers are similar to
detrivores
 Break down dead organisms by
releasing digestive enzymes (fungi)
 Important because they make
nutrients available for all other
organisms


Ecologists use food chains and food webs to
show energy flow in ecosystems
Trophic level
◦ Each step in a food chain or food web
◦ Autotrophs are the first trophic level in ALL food
chains and food webs!

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Primary producers:
make their own food
Primary consumers:
eat the primary
producers
Secondary consumers:
eat the primary
consumers
Third-level consumers:
eat the secondary
consumers

Food chains: a simple
model that shows how
energy flows through an
ecosystem
◦ Arrows show one-way energy
flow
◦ Each organism uses some of
the energy from the organism
it eats
 The remaining energy
is lost to the
surrounding
environment

Food webs: models that
represent the
interconnected food chains
in which energy flows
through a group of
organisms

Diagrams that show
the relative amounts
of energy, biomass or
numbers of organisms
at each trophic level
◦ Biomass is the total mass
of living matter at each
trophic level

Approximately 90% of
all energy at a tropic
level is NOT
transferred to the
level above it




Energy is not recycled in a ecosystem
Matter (biomass) is recycled in a ecosystem
◦ Nutrient: a chemical substance that an organism
needs from its environment.
Nutrient cycling involves both the biotic and abiotic
portions of an ecosystem.
These are called the biogeochemical cycles.
The Water Cycle: more of a physical
process than a chemical one.

Key Terms:
◦ Evaporation: water returning to the atmosphere
from oceans, lakes, and rivers
◦ Transpiration: water returning to the atmosphere
from the surface of plants
◦ Precipitation: water returning to the earth from the
atmosphere
◦ Percolation: water running through the soil
◦ Runoff: water running on the surface of the earth.

Two natural processes help to cycle carbon
through the ecosystem.
◦ Photosynthesis:
 autotrophs
 take in CO2 and produce organic compounds
 Make them available then for consumers.
◦ Cellular Respiration;
 both autotrophs and heterotrophs
 convert energy rich organic compounds into ATP
 powers cellular functions.

Deposition
◦ dead materials:
◦ converted to peat, coal, oil or gas deposits (carbon
stored as fossil fuel)
◦ carbon is released when fossil fuels are burned

Carbonate in sediments:
◦ shells, coral, algae fall to bottom of ocean creating
limestone rock.
◦ Carbon is released in the form of bicarbonates
The Carbon Cycle
Try to count the number of black dots on the image below...
There are none!

Nitrogen enters ecosystems through two
natural pathways.
◦ Nitrogen fixation, where certain bacteria convert N2
to minerals that can eventually be used by plants to
produce nitrogenous organic compounds.

Chemical nitrogen fixation - lighting bolts change

Some bacteria break down detritus and animal
waste producing ammonium through
nitrogen gas to nitrates or nitrogen is added to the
soil by chemical fertilization.
Ammonification


Certain bacteria convert ammonium into nitrate, a
process called Nitrification.
Nitrate can be used by plants.

Some bacteria take oxygen from the nitrate
and release N2 back into the atmosphere
called Denitrification.
PROCESS
By What
Organism
Compounds
Used
WHAT IS PRODUCED
(Products)
NITROGEN FIXATION
Nitrogen fixing
bacteria in soil
and in legume
roots.
Nitrogen Gas
(N2)
Usable nitrogen:
Nitrates (NO3-) made in
roots of legumes and
Ammonium (NH4+) and in
the soil.
AMMONIFICATION
Decomposers
(Bacteria and
Fungus)
Detritus and
waste
Ammonia
NITRIFICATION
Nitrifying Bacteria
Ammonium
Nitrites (NO2-) & NO3-
ASSIMILATION
Chemical
reactions in the
organism.
Nitrates
Any nitrogen based
compound needed by
plants and animals.
Nitrogen is used to make
amino acids.
Denitrifying
Bacteria
Excess
nitrates
Nitrogen Gas
DENITRIFICATION
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
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Needed for growth and development
Short term- cycled from soil to producers and
producers to consumers
Long term- Phosphorus comes from
weathering and erosion of rocks

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Decomposition rates largely determine the rates of
nutrient cycling
The rate at which nutrients cycle in an ecosystem
depends on the rate of decomposition.
◦ Decomposition can take up to 50 years in the tundra, while
in the tropical forest, it occurs much faster.

Quantities of nutrients in the soil of different
ecosystems also varies, depending on the rate of
absorption by the plants.


In a terrestrial ecosystem most of the
mineral nutrients cycle within the
ecosystem.
In addition to the natural ways, nitrogencontaining fertilizer contributes to the total
amount of nitrogen materials in
ecosystems.