Ecology:
Ecosystem
An ecosystem is a community of
organisms and their environment
Outline
1. Key concepts
2. The Nature of Ecosystems
3. Structure of Ecosystems
4. Food chains and webs
5. Pyramids
6. Key terms
7. Conclusions
Key Concepts:
An ecosystem is an association of organisms and their
environment
Every ecosystem is an open system, in that it has
inputs and outputs of both energy and nutrients
Energy flows in only one direction through an
ecosystem
Each chain in a food web extends in a straight-line
sequence from producers through all the consumers
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The Nature of Ecosystems
An ecosystem is a community of organisms and
their environment
•
•
•
Biotic components: producers and consumers
(including decomposers)
Nutrients recycle within ecosystems and energy
flows through ecosystems (does not recycle) in a
regulated fashion
Ecosystems have boundaries which may be clearly
defined or overlap and continually changing
The Nature of Ecosystems
Primary
producers
Consumers
Decomposers
The Nature of Ecosystems
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Trophic Levels in Prairie
Fourth-level consumers (heterotrophs):
Top carnivores, parasites,
detritivores, decomposers
5th
Third-level consumers (heterotrophs):
Carnivores, parasites, detritivores,
decomposers
4th
Second-level consumers (heterotrophs):
3rd
Carnivores, parasites, detritivores,
decomposers
First-level consumers
(heterotrophs):
2nd
Herbivores, parasites, detritivores,
decomposers
Primary producers (autotrophs):
1st
Photoautotrophs, chemoautotrophs
Food chains and webs
Nutrients cycle and energy flows through
ecosystems
Food chain composed of linear connections
between trophic levels of:
· Producers
· Primary consumers
· Secondary or tertiary consumers
· Decomposers
Food web: formed by interconnections between
and among food chains
Food Chain
MARSH
HAWK
A straight line
sequence of who eats
UPLAND
SANDPIPER
whom
Simple food chains are
GARTER SNAKE
rare in nature
CUTWORM
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Food
chains
and
webs
Energy Losses
Energy transfers are never 100 percent
efficient
Some energy is lost at each step
Limits the number of trophic levels in an
ecosystem
Pyramids
Each trophic level has less biomass,
fewer organisms and less useable
energy than the one below it
• Energy is lost at each step to:
· heat
· organism’s activities
· growth and reproduction
•
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Pyramids
•
Different kinds of pyramids:
· Biomass (total weight of organisms)
· Energy (flow through a level)
· Numbers (total number of
organisms)
Pyramids
Pyramids of biomass represent the ecological
consequence of low trophic efficiencies.
Most biomass pyramids narrow sharply from
primary producers to top-level carnivores
because energy transfers are inefficient.
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Pyramid
of Energy
Pyramids of numbers show how the levels in the
pyramids of biomass are proportional to the
number of individuals present in each trophic
level.
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– The dynamics of energy through ecosystems
have important implications for the human
population.
Ecosystem
Trophic level
Primary producers
Primary consumers
Secondary consumers
Tertiary consumers
Detritivores
Food chain
Food web
Biomass
Biomass pyramid
In Conclusion
An ecosystem is an array of producers,
consumers, and decomposers and their
environment
Sunlight is the initial energy source for nearly all
ecosystems
Feeding relationships are structured as trophic
levels in an ecosystem
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