Lecture #2
How Ecosystems Work
Biosphere Breakdown
Organism-any form of life (1 individual)
Species- all organisms of the same kind that
are genetically similar enough to breed in
nature and produce live, fertile offspring
Population-individuals of the same species in
an area
Biological Community-populations of different
species living & interacting in a given area
Ecosystem-many interacting communities in a
specific place including abiotic factors
Biome- large terrestrial regions characterized by
a distinct climate & specific life–forms,
especially vegetation, adapted to the region
Ecosphere-(=biosphere)-all of Earth’s biomes
together
Ecosystem
Physical
environment
Abiotic factors
atmosphere
soil
water
wind speed
wind direction
current velocity
Community
Biotic factors
competitors
symbionts
predators
parasites
pathogens
What drives an ecosystem?
• Photosynthesis is at the base of all ecosystems so
photosynthesizers (usually plants) are called the
producers.
• Productivity - the amount of biomass produced in a
given area in a given period of time. Photosynthesis
is called primary productivity because it is basic to all
other growth in an ecosystem.
• Secondary productivity - manufacture of biomass by
organisms that eat plants
From Species to Ecosystems
• Ecosystem - biological community (biotic factors) and
its physical environment (abiotic factors)
– The elements are interacting to process energy
and cycle materials
– Most ecosystems are open in that they exchange
materials and organisms with other ecosystems.
– It is difficult to define the boundaries of an
ecosystem.
Major Components of Ecosystems
Major components of aquatic ecosystems.
© Brooks/Cole Publishing Company / ITP
Food Chains and Food Webs
Food Chain - A sequence
that shows the manner
in which energy is
transferred from one
organism to another , as
each organism eats
another, in an
ecosystem.
Food web –a complex of interconnected food chains in
an ecosystem.
• These show the many feeding relationships in an
ecosystem.
• In an ecosystem of average complexity, numerous
pathways are possible.
• Food webs are a more realistic model of the flow of
energy and materials through an ecosystem.
Trophic pyramids
• Food Chains can also be
represented by an ecological
pyramid by arranging the
organisms at various trophic
levels diagrammatically.
• Notice that there are many
more producers than
consumers.
• Each trophic level consists
of organisms that get their
energy in the same way.
Which organisms make up each
trophic level?
• Plants (producers) make up the first trophic level.
Animals are consumers.
• 2nd trophic level: Primary Consumers:- Animals that
eat plants.
• 3rd trophic level: Secondary Consumers- Animals
that eat primary consumers
• 4th trophic level: Tertiary consumers- Animals that
eat secondary consumers
* Organisms may occupy more than one trophic level!
• Organisms can also be identified by the type of food
they consume:
•
What they eat
Examples
– Herbivores (Plants)
{Deer}
– Carnivores (Meat)
{Wolves}
– Omnivores (Plants/Meat)
{Bears}
– Scavengers (Carcasses)
{Crows}
– Detritivores (Debris)
{Ants}
– Decomposers (All)
{Bacteria}
Ecological Pyramids & Energy
Transfer
• Due to the Second Law of Thermodynamics, energy is lost at
each level of the pyramid.
• 10% Rule (Energy / Biomass) - as an organism is consumed,
about 90% of the energy at each trophic level is lost or used
up along the way (as heat in metabolic processes).
• Only about 10% of the energy becomes part of the consumers
body.
• This 10% is all that is available to the next trophic level when
one organism consumes another.
Examples
» 1 kg fox
» 10 kg rabbit
» 100 kg clover