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Chapter 4
Ecosystems:
Components, Energy
Flow, & Matter Cycling
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Chapter Outline
1. Ecosystem Concepts
• Components and organization of Ecology
2. Food Webs & Energy Flow
• autotrophs, heterotrophs, productivity, efficiency
3. Nutrient Cycles
• water, carbon, nitrogen, phosphorus
4. Ecosystem Services
• importance of ecosystems
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Ecosystem Concepts
Ecology: study of relationships between
organisms & their environment
biosphere
ecosystem
community
Realm of ecology
population
organism
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Organism
• organism: any form of life
•classified into species
• species: groups of organisms that resemble each other
and can potentially interbreed
•There are estimated to be 3.6 - 100 million species
•Only about 1.8 million species named
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Population
• Population: a group of interacting individuals of the
same species
Examples:
• sunfish in a pond
• white oak trees in a forest
• people in a city
• habitat: the place where a population usually lives
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Communities
• Communities: populations of all species living
together in a given area
• Example:
• Redwood forest community - consisting of
populations of redwood trees, other trees,
shrubs, animals, and microorganisms
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Ecosystem
•Ecosystem: a community of different species
interacting with one another & with their non–living
environment of matter & energy
• Examples:
• a patch of woods
• a lake or pond
• a farm field
• an entire watershed in a tropical rain forest
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Biome
• Biomes: large land area characterized by a distinct
climate & specific populations
• Major biomes:
• temperate grassland
• temperate deciduous forest
• desert
• tropical rain forest
• tropical deciduous forest
• tropical savannah
• coniferous forest
• tundra
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Aquatic Life Zone
Aquatic Life Zone: major marine or freshwater
portion of the ecosphere, containing numerous
ecosystems
• Major aquatic life zones:
•lakes
•streams
•estuaries
•coastlines
•coral reefs
•deep ocean
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Major Components of Ecosystems
abiotic: non-living components
e.g., water, air, nutrients, & solar energy
biotic: living components
e.g, plants, animals, & microorganisms
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Biotic Components
• producers (autotrophs "self–feeders"): make
their own food from abiotic compounds.
• most by photosynthesis, e.g., green plants
• a few by chemosynthesis, e.g., some bacteria
• consumers (heterotrophs "other–feeders"): get
their energy & nutrients by feeding on other
organisms or their remains.
• herbivores
• carnivores
• decomposers
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Consumers (heterotrophs)
• primary consumers: (herbivores) feed directly on
producers
• secondary consumers: (carnivores) feed on primary
consumers
• tertiary consumers: feed on carnivores
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Consumers (heterotrophs)
• omnivores: consumers that
feed on both plants & animals
Consumers (heterotrophs)
• scavengers: feed on dead organisms
Consumers (heterotrophs)
• decomposers: consumers
that complete the breakdown
& recycling of organic
materials from the remains &
wastes of other organisms
Consumers (heterotrophs)
• detritivores: feed on detritus (partially decomposed
organic matter, such as leaf litter & animal dung)
Decomposers
Aquatic
Ecosystems
Terrestrial
Ecosystems
Limiting Factor
Limiting Factor: an environmental factor that is
more important than other factors in regulating
survival, growth, or reproduction
• too much or too little of any abiotic factor can
limit or prevent growth
• tolerance: distribution & abundance of a
species determined by range of physical or
chemical factors
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Range of Tolerance
Photosynthesis
complex chemical reaction in plants, in which solar
radiation is captured by chlorophyll (& other
pigments) & used to combine carbon dioxide & water
to produce carbohydrates (e.g., glucose), other
organic compounds, & oxygen
6 CO2 + 6 H2O + solar energy
C6H12O6 + O2
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Respiration
complex process that occurs in the cells of
organisms, in which organic molecules (e.g.,
glucose) are combined with oxygen to produce
carbon dioxide & water, & release energy
C6H12O6+ O2
6 CO2 + 6 H2O + energy
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Summary of Ecosystem
Structure
Fig. 4–13
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2. Food Webs & Energy Flow
Fig. 4–14
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A Food Web in Antarctica
Fig. 4–15
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A Grazing Food Web
Fig. 4–18a
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Energy Pyramid
• ecological
efficiency
5% to 20%
• 10% efficiency
general rule
Fig. 4–16
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Generalized Energy Pyramid
Fig. 4–17
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Biomass Pyramids
Fig. 4–18
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Pyramids of Numbers
Fig. 4–19
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Primary Productivity
gross primary productivity (GPP): the rate at
which an ecosystem's producers convert solar
energy into chemical energy as biomass
net primary productivity (NPP): the rate at which
energy for use by consumers is stored in new
biomass
NPP = GPP – [rate producers use biomass]
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Primary Productivity (per area)
Fig. 4–21
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Primary Productivity (total)
Fig. 4–22
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Nutrient Cycling & Sustainability
• ecosystems tend toward equilibrium with respect
to energy flow & nutrient cycling; may appear
self–contained;
• “immature” natural ecosytems -- major shifts in
energy flow & nutrient cycling;
• ecosystems not self-contained -- considerable
exchange of water & nutrients of ecosystems with
adjacent ecosystems;
• human modification of nutrient cycles can lead to
major shifts in ecosystem function.
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4. Ecosystem Services
natural benefits that support life on the earth
& are essential to the quality of human life &
the functioning of the world's economies
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Examples of Ecosystem Services
• control & moderate climate
• recycle vital nutrients
• provide energy & mineral resources
• furnish food, fiber, medicine, timber, & paper
• pollinate crops & useful native plants
• absorb, dilute, or detoxify pollutants
• control populations of pests & disease organisms
• slow soil erosion & prevent flooding
• provide biodiversity of genes & species
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Why is biodiversity important?
• material benefits
• ecosystem services
• aesthetic benefits
Two principles of sustainability?
• use renewable solar energy
• recycle nutrients needed for survival,
growth, & reproduction
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Why is an understanding of ecology
essential for environmental
science?
• understanding the scientific basis for
interdependence & connectedness
• solving environmental problems
• ensuring sustainability
• high–quality life for humans
• high–quality life for other organisms.
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The problems of the human future range far
beyond ecology, yet ecology is an essential
part of them.
– Robert H. Whittaker
All things come from earth, and to earth they
all return.
– Menander (342–290 B.C.)
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