Ecosystems
Vocabulary
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Abiotic factor
Biomass
Carnivore
Ecosystem
Food web
Humus
Omnivore
Pyramid of biomass
Pyramid of numbers
First-order consumers
Second-order consumers
Third-order consumers
algal bloom
biotic factor
commensalism
estivation
herbivore
niche
trophic level
pyramid of energy
Interactions Among Organisms
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In every
community,
organisms interact
with one another.
The relationships
between the
different organisms
is known as the
biotic factor in an
environment.
Biotic Factor is the relationship between living things
The interaction of a
community with its
environment is an
ecological system
also called an
ecosystem.
 In almost all
ecosystems, the
original source of
energy starts with
the sun.
 Tropical grassland
ecosystem
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Interactions
between organisms
involve the
exchange of
energy, usually by
feeding upon one
another. Thus,
each organism
represents a
feeding step called
a trophic level.
Marine trophic level
Niche
A niche describes
how an organism
fits into an
ecosystem.
 Because each
organism is
unique, no two
organisms can
occupy the same
niche in an
ecosystem.
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Trophic levels
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Producer (plants,
Autotrophs or
Photoautotrophs)
First-order consumers
(herbivores)
Second-order consumer
(carnivores)
Third-order consumer
(large carnivores)
Decomposers are
consumers as well.
Omnivores eat both plants
and animals.
Food Chains
Which is which?
Decomposers
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When any organism
dies, it is eventually
eaten by detrivores
(like vultures, worms
and crabs) and broken
down by
decomposers
(mostly bacteria and
fungi), and the
exchange of energy
continues.
Food Web
All the possible
feeding
relationships that
exist in an
ecosystem make
up a food web.
 What are the
primary producers,
1st, 2nd and 3rd
consumers in this
marine food web?
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Marine Food Web
Pyramid of Energy
 The
transfer of energy within an
ecosystem is called the pyramid of
energy.
 Energy originally produced is not
lost, just changed into different
forms of energy such as heat.
 Energy can also be stored—more
than ½ of the potential energy in
each food molecule is lost as heat
energy during cellular respiration.
Pyramid of numbers
The loss of energy
between the
trophic levels
explains why there
are fewer
organisms in each
higher level than
the previous one.
 This relationship is
called the pyramid
of numbers.
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The pyramid of
numbers does not
apply to all food
chains. An
exception would be
where a large
organism is fed
upon by smaller
ones. Example: a
dog infested with
parasites.
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Biomass is the amount
of dried organic
matter at different
trophic levels.
Most ecosystems have
a pyramid of biomass.
Aquatic systems do
not form a pyramid
because most of the
producers are
microscopic algae.
Commensalism
Commensalism occurs
when one organism
benefits from another
without aiding or
harming the host.
 Remoras are
“hitchhiker” fish that
eat the leftovers of
larger fish. They don’t
help or hurt the fish,
so it’s a commensal
relationship.
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Whaleshark and remora
Carbon Cycle in an Ecosystem
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Energy is not cycled
but replaced by
sunlight’s energy.
Carbon dioxide from
aerobic respiration,
fuel emissions and
volcanic activity is
recycled into organic
and inorganic
substances.
Click for Carbon Cycle
Mutualism
Mutualism is a
mutually beneficial
relationship
between
organisms.
 The bee feeds on
the flower and
pollinates it at the
same time. Both
benefit.
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Coral Reef Ecosystem
Bee and flower
Parasitism
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A parasite is an
organism who is
dependent upon a
host.
Indian paintbrush
(Castilleja indivisa) is
a parasitic plant that
obtains some of its
nutrients and water
from host plant-bluebonnet (Lupinus
texensis).
Indian paintbrush and bluebonnet
Abiotic Factors of the
Environment
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Physical aspects of an
ecosystem affect the
reproduction, feeding,
growth and
metabolism of
organisms within that
system.
Abiotic factors
include:
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Water
Soil
Light
Temperature
Abiotic Factors are
the relationship
between non-living
things.
All organisms need
water.
 Available water is a
limiting factor for
organisms.
 Evaporation,
condensation and
precipitation are
the primary phases
in the water cycle.
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Water cycle (click here)
Soil
Soil is important to organisms
because it’s where plants
grow and animals make their
homes.
 Soil holds many
microorganisms and
decomposers that are
important for the cycling of
materials.
 Humus is the decayed
remains of organisms in soil.
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Soil layers
Let there be Light
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Light is the source of
energy for almost all
ecosystems. It
provides the energy
for photosynthesis:
6CO2 + 6H2 O  C6H12O6 + 6O2
Light is also required
for vision, and heat
absorption that results
in evaporation.
Temperature
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Organisms are
adapted to survive
within particular
temperature ranges.
Temperatures change
from day to night and
season to season.
Temperature and day
length can cause
mammals to migrate
or hibernate in winter.
Metabolic rate
decreases during
hibernation.
Hazel dormouse hibernating in burrow
 Temperature
can also affect
metabolic rate (activity of enzymes).
Organisms cannot survive above
50oC because enzymes are
destroyed.
 Lizards compensate for desert heat
by shading up during the day while
some frogs go dormant.
 Summer dormancy is called
estivation.
Sand diving lizard
Disrupting the Balance
An ecosystem can be
temporarily altered by
biotic and abiotic factors.
 Both these factors help
regulate population sizes
in that resources are not
overused.
 Naturally occurring
disruptions include floods,
earthquakes and
volcanoes.
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Human Activities and Nature’s
Balance
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Certain human
activities can alter
nature’s delicate
balance.
Too many phosphates
from detergents can
increase algae,
creating an algal
bloom that eventually
suffocates other
organisms.