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Chapter 5:
Ecosystems: Concepts and
Fundamentals
Overview
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The Ecosystem: Sustaining Life on Earth
Ecosystem Communities and Food Chains
Ecosystems as Systems
Biological Production and Ecosystem Energy
Flow
Biological Production and Biomass
Energy Efficiency and Transfer Efficiency
Ecological Stability and Succession
Chemical Cycling and Succession
How Species Change Succession
The Ecosystem: Sustaining Life
on Earth
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Sustaining life on Earth requires more
than individuals
Ecosystem
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Interactions of many organisms functioning
together in ecosystems
Physical and chemical environments
Basic Characteristics of Ecosystems
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Ecosystems have several fundamental
characteristics
Grouped into
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Structure
Processes
Basic Characteristics of Ecosystems
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Structure
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Made up of two major parts
Living (ecological community)
 Non living (physical & chemical environment)
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Processes
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Cycling of chemical elements
Flow of energy
Basic Characteristics of Ecosystems
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At its simplest a
community will have:
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At least one species
that is a producer
Another species that
is a decomposer
Plus a fluid medium
Never this simple
Basic Characteristics of
Ecosystems
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Ecosystem chemical cycling
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For complete recycling of chemical
elements, several species must interact
Photosynthetic organisms produce sugar from
carbon dioxide and water
 From sugar and inorganic compound they make
other organic compounds (protein, woody
tissue)
 Need decomposers to get back to inorganic
compounds
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Ecological Communities and Food
Chains
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Ecological community definitions
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A set of interacting species found in the same
place and functioning together to maintain life
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In practice it is difficult to identify the interacting
species
All the species found in an area, whether or
not they interact
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Operational definition
Food Chains
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Food chain
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Linkage of who feeds on whom
Energy, chemicals and some compounds are
transferred from creature to creature along
food chains or food webs (more complex)
Grouped by trophic level
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Number of feeding levels away from original
source of energy
Trophic Levels
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First trophic level
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Use energy from the sun and carbon dioxide
from the air to photosynthesizes
Green plants, algae and certain bacteria
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Called autotrophs
Second trophic level
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Organisms that feed on autotrophs
Called herbivores
Trophic Levels
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Third trophic level
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Forth trophic level
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Feed directly on herbivores
Called carnivores (meat eaters)
Carnivores that feed on third-level carnivores
Decomposers- feed on waste and dead
organisms of all trophic levels
A Food Chain Example
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Example: Yellowstone Hot
Springs
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1st level - photosynthetic algae
and bacteria
2nd level - Ephydrid flies (larvae
feed on the bacteria and algae)
3rd level - dolichopodid fly
(larvae feed on herbivorous
flies)
4th level - parasites and
predators to the flies
An Oceanic Food Chain
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Tend to have more trophic levels
1st level - planktonic algae and planktonic
bacteria
2nd level - zooplankton and some fish
3rd level - fish and invertebrates feed on
herbivores, baleen whales
4th+ levels - killer whales, predatory fish
Complex Food Web - Harp Seal
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Most species feed on several trophic levels
Harp seal (shown at 5th level)
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Feeds on flatfish (4th level)
But also feed on foods from 2nd – 4th
A species that feeds on several levels placed
in a category one above the highest level it
feeds on
Ecosystem as Systems
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An ecosystem is the minimal entity that
has the properties required to sustain life
Vary greatly in:
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Structural complexity and clarity of their
boundaries
Size
Composition
Proportion of non-biological constituents
Degree of variation in time and space
Sharp and Distinct Transition - lake
to forest
Watershed
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Watershed
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Commonly used
practical delineation
of the boundary of
an ecosystem
Determined by
topography
United in terms of
chemical cycling
Ecosystem Energy flow
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All life requires energy
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Ability to do work
Ecosystem energy flow
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Movement of energy through an ecosystem
from the external environment through a
series of organisms and back to the external
environment
Energy Flow
Energy enters an ecosystem by two
pathways:
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1.
2.
Energy fixed by organisms
Transfer of heat energy by air, water, soil
and warm living things
Ecosystem Energy Flow
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Energy is difficult and abstract concept
Most of the time energy is invisible to us
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With infrared film we can see difference
between warm and cold object
Birch forest in New Hampshire
Regular film
Infrared film
A nearby rocky outcrop
Regular film
Infrared film
Laws of Thermodynamics
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First Law of Thermodynamics
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Law of conservation of energy
In any physical or chemical change, energy is
neither created nor destroyed
Energy merely changed from one form to
another
If this is true, why can’t we continually
recycle energy within our bodies?
Impossible ecosystem because of 2nd law of thermodynamics
Laws of Thermodynamics
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Energy must continually be added to an
ecological system in a usable form
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Because inevitably degraded into heat
Net flow of energy is a one way flow
Second Law of Thermodynamics
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No use of energy is ever 100% efficient
Energy is lost to heat
Energy Efficiency
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As energy flows through a food web, it is
degraded, and less and less is useable
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Entropy
Energy must be continually added to an
ecosystem, in usable form
Biological Production
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Biomass
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Total amount of organic matter on Earth or in
any ecosystem or area
Measured as the amount per unit surface area
Biological production
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Capture of usable energy from the
environment to produce organic compounds
Biological Production
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Gross Production
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Net Production
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Increase in stored energy before any is used
Change in biomass over a given time
Three measures used for biological
production
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Biomass
Energy stored
Carbon stored
Two Kinds of Biological Production
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Primary Production
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Autotrophs (& chemoautotrophs)
Photosynthesize or chemosynthesize
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Make their own organic matter from energy
source and inorganic compounds
Secondary production
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Heterotrophs
Cannot make their own organic compounds
and must feed on other living things
Biological Production
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Respiration
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Use of energy from organic matter by most
heterotrophic and autotrophic organisms
Organic matter combines with oxygen
 Releases energy, carbon dioxide and water
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Use of biomass to release energy that can be
used to do work
Energy Efficiency and Transfer
Efficiency
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Trophic-level efficiency
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Ratio of production of one trophic level to the
production of the next trophic level
Never very high
1–3% in natural ecosystems
 10% may be maximum
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90% of all energy lost as heat
Ecological Stability and Succession
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Ecosystems are dynamic- always changing
Primary succession
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Establishment and development of an ecosystem
where one did not exist previously (lava flow left; edge of retreating glacier - right)
Ecological Stability and Succession
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Secondary succession
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Reestablishment of an ecosystem following
disturbance
Remnants of previous biological community
(soil, seeds, organic material, etc.)
Examples
Forests that develop on abandoned pastures
 Development after hurricanes, floods, fires
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Dune Succession
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Sand dunes continually formed along
sandy shores
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Breached and destroyed by storms
After dune forms
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Grasses establish
Grass runners stabilize
dunes
Other species seeds
may germinate and
become established
Bog Succession
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Bog - Open body of water with surface
inlets but no surface outlets
Succession:
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Sedge puts out floating runners
Wind blows particles into the mat of runners
Seeds land on runners and germinate
Mat becomes thicker and shrubs and trees
develop
Bog Succession
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Bog also fills in from the bottom
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At the shore, floating mat and sediment meet
forming a solid surface
Farther from shore all the vegetation is still
floating
General Patterns of Succession
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Successional stages
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Early (1 and 2), middle, and late
Similar patterns seen with animals and
other life-forms at each stage
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Pioneers - species characteristic of early stage
Late-successional species tend to be slowergrowing and longer-lived
General Patterns of Succession
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In early stages of succession
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Biomass and biological diversity increase
In middle stages
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Gross production increase and net production
decrease
Organic material in soil increases, as does
chemical element storage
How Species Change Succession
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Earlier succession species affect what
happens later in succession through:
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Facilitation
Interference
Life history differences
Facilitation
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Facilitators in dune and bog succession
are dune grass and floating sedge,
respectively
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They prepare the way for other species
Interference
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Certain early species interfere with the
entrance of other species
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Grasses may form dense mats blocking other
seeds from germinating
Chronic Patchiness
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Common in deserts
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Major shrub species grow in
patches
Patch persist for long period
of time until next
disturbance
Life tends to build up
Non-biological processes
tend to erode or degrade
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In harsh environments
degrading dominates and
succession does not occur