Visualizing Environmental Science
How Ecosystems Work
Chapter 5
Chapter
Chapter77
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Solving Lake Washington’s Ecological
Imbalance
• Effluent released into the large freshwater lake
raised the levels of the nutrient phosphorus present
in the water
― In 1955, scientists linked high phosphorus levels to increased
cyanobacterial growth
― Large mats of cyanobacteria had formed a thick green scum on
the surface
― This led to explosive growth of bacteria that decompose the
cyanobacteria, which, in turn, used up large quantities of
dissolved oxygen in the lake
― Larger organisms were then affected by this oxygen depletion,
and fish and small invertebrates began to die
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Solving Lake Washington’s Ecological Imbalance
• Beginning in 1963, effluent was diverted from the lake, and by 1968, all
sewage input into the lake had ceased
― The lake’s condition began to improve, and the water to clear
― No further cyanobacteria overgrowth has occurred since, and the lake
remains clear to this day
Dissolved phosphorus in Lake Washington from 1955
to 1974. Note that the level of dissolved phosphorus
declined in the lake as the phosphorus contributed
by sewage effluent (shaded area) declined.
Cyanobacterial growth from 1964 to 1975, during Lake
Washington’s recovery, as measured indirectly by the amount of
chlorophyll, the pigment involved in photosynthesis. Note that
as the level of phosphorus dropped in the lake, the number of
cyanobacteria (that is, the chlorophyll content) declined.
© 2017 John Wiley & Sons, Inc. All rights reserved.
What is Ecology?
• Ernst Haeckel
• The study of the
interactions among
organisms and
between organisms
and their abiotic
environment
• Biotic and abiotic
• Linked to geology,
chemistry, physics
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What is Ecology?
• Levels of organization
– Population: A group of organisms of the same
species that live in the same place at the same
time
– Communities: All the populations of different
species that live and interact together within an
area at the same time
– Ecosystem: A community and its physical
environment
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What is Ecology?
• Levels of organization
– Landscape: A region that includes several
interacting ecosystems
• Landscape ecology studies the connections among
ecosystems in a given region
– Biosphere: The parts of Earth’s atmosphere, ocean,
land surface, and soil that contain all living
organisms
• Compare atmosphere, lithosphere , hydrosphere
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The Flow of Energy Through Ecosystems
• Energy—the ability to do work
– Potential energy = stored energy
– Kinetic energy = energy of motion
• Thermodynamics—the study of energy and its
transformations
– First and second law of thermodynamics
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The Flow of Energy Through Ecosystems
Potential and kinetic energy
Potential energy is stored in the drawn bow (a) and is converted to kinetic energy (b) as
the arrow speeds toward its target.
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The First Law of Thermodynamics
• Energy cannot be
created or destroyed
• Total energy content of
an organism and its
surroundings is always
the same
• However, energy can
change from one form
to another
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The First Law of Thermodynamics
• Photosynthesis
– Plants capture light energy from the sun, and convert it
into stored chemical energy
– This captured energy is then released during cellular
respiration, and is used by the organism to do biological
work
– The chemical equation for photosynthesis is:
• 6C02 + 12H2O + radiant energy → C6H12O6 + 6H2O + 6O2
– The chemical equation for cellular respiration is:
• C6H12O6 + 6O2 + 6H2O → 6CO2 + 12H2O + energy
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The Second Law of Thermodynamics
• The amount of usable energy in the universe decreases
over time, as some is lost as heat
– Heat: Less usable and more disorganized form of energy
• Within living organisms, during each energy
transformation some energy is changed to heat
– No organism can use this heat energy for biological work
• Entropy—a measure of this disordered energy
• No process that requires energy is 100% efficient, as much
energy is transformed to heat and becomes unusable for
work
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Producers, Consumers, and Decomposers
• Producers, consumers and
decomposers
– Three categories based on how
nourishment is obtained
• Producers manufacture large
organic molecules from simple
inorganic molecules
– Producers are potential food for
other organisms
– Plants are the most significant
producers on land
– Algae and certain bacteria are
the important producers in
aquatic environments
This moose is a herbivore, or
primary consumer, utilizing the
chemical energy stored in grasses
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Producers, Consumers, and Decomposers
• Consumers are animals that
consume other organisms
– Primary consumers, or
herbivores, eat producers
– Secondary consumers eat
primary consumers
– Tertiary consumers eat
secondary consumers
• Secondary and tertiary
consumers are carnivores
• Consumers that eat both plants
and animals are omnivores
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Producers, Consumers, and Decomposers
• Detritivores—consumers, such
as this crab, that eat waste
organic matter
• Decomposers—bacteria and
fungi that break down dead
organisms
• Detritivores and decomposers
are important for ecosystem
health, and work together to
prevent a build-up of organic
waste
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The Path of Energy Flow in Ecosystems
• Energy flow—the passage of energy in a one-way direction
through an ecosystem, occurs in food chains
• Trophic level—each level in a food chain
• Energy is lost as heat along the way, thus the number of steps in
a food chain is limited, and less energy is available for organisms
at the higher trophic levels
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The Path of Energy Flow in Ecosystems
• A food web is a
complex of
interconnected food
chains in an ecosystem
• A food web gives a
more realistic view of
the flow of energy in
an ecosystem than the
simple path shown in
a food chain
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The Path of Energy Flow in Ecosystems
• Ecological pyramids graphically
represent the relative energy
values of each trophic level
• Pyramids of numbers show the
number of organisms at each
trophic level in a given
ecosystem
• Pyramids of energy illustrate
how energy dissipates into the
environment as it moves from
one trophic level to the next
This pyramid of numbers represents
10,000 grass plants supporting 10
mice, which support one bird of prey.
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Ecosystem Productivity
• Gross primary productivity (GPP) is
the rate at which energy is
captured during photosynthesis
• Net primary productivity (NPP) is
the amount of biomass found in
excess of that broken down by a
plant during cellular respiration
– Only the energy represented by NPP is
available as food for an ecosystem’s
consumers
– Humans use a much higher
percentage of global NPP than all
other animal species
NPP is expressed in grams of dry matter
produced per square meter per year for
the selected ecosystems
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The Cycling of Matter in Ecosystems
• Biogeochemical cycles
– Matter—the material of which organisms are
composed
– Biogeochemical cycles involve biological, geological,
and chemical processes
– Humans have GREAT influence
– Cycling vs. flow
• Matter cycles through ecosystem
– From abiotic environment to organisms, then back to environment
• Energy flows through the ecosystem
– From producers to consumers to decomposers, finally to be
released as heat energy
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The Cycling of Matter in Ecosystems
• Matter cycles between
the biotic and abiotic
environments as it
moves from one part
of the ecosystem to
another
– Carbon, hydrologic,
nitrogen, sulfur, and
phosphorus are all
biogeochemical cycles
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The Carbon Cycle
• The global movement of carbon between the
abiotic environment (atmosphere, ocean) and
organisms
– Atmosphere/ocean  photosynthesis  cellular
respiration/combustion/decomposition 
atmosphere/ocean
• Carbon is an essential component of organisms’
molecules
• Also essential component of abiotic environment
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The Carbon Cycle
• Carbon makes up 0.04% of
the atmosphere
• Needed to make proteins
and carbohydrates
• Present in several forms
such as CO2, HCO3–, CaCO3
• Photosynthesis fixes
carbon from CO2 into
carbohydrates
• Fossil fuels, coal, oil and
natural gas are deposits of
carbon compounds
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The Hydrologic Cycle
• Water circulates among the
ocean, land, and atmosphere
• The hydrologic cycle provides
a renewable supply of water
for terrestrial organisms
– Runoff is the movement of
water from land to rivers and
lakes
– Watersheds are areas of land
where runoff drains
• Climate change and aerosols,
a type of air pollutant,
weaken the hydrologic cycle
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The Nitrogen Cycle
• Nitrogen is an essential component
of proteins and nucleic acids
• Atmosphere is 78% nitrogen gas
• Nitrogen gas molecules must be
broken apart before the nitrogen
can be used in proteins and
nucleic acids
• Five steps in which nitrogen cycles
between the abiotic environment
and organisms
–
–
–
–
–
Nitrogen fixation
Nitrification
Assimilation
Ammonification
Denitrification
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The Nitrogen Cycle
• Nitrogen fixation converts
atmospheric nitrogen gas to
a form that organisms can
use (NH3)
• Nitrogen-fixing bacteria
carry out nitrogen fixation
in soil and aquatic
environments
• Photochemical smog and
acid deposition are
nitrogen-based air
pollutants
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The Sulfur Cycle
• Bacteria-driven cycle
• Sulfur is primarily found
underground in sedimentary
rocks and minerals, and in the
ocean
• Available in other forms such as
SOx, H2SO4, and H2S
• Sulfur gas is a minor part of the
atmosphere, but has substantial
movement in/out of atmosphere
• Sulfur is a necessary component
of proteins
• Animals get sulfur from plant
protein
• Burning coal releases sulfur,
which causes acid deposition
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The Phosphorus Cycle
• No atmospheric component
• Phosphorus cycles between
land and organisms
• Phosphorus in soil is
absorbed by plant roots
– Necessary to make nucleic
acids and ATP
• Humans accelerate loss of
phosphorus from the land
• Phosphorus in fertilizers can
cause eutrophication, as in
Lake Washington (chapter
opener)
© 2017 John Wiley & Sons, Inc. All rights reserved.
Ecological Niches
• Ecological niche
– The totality of an organism’s adaptations, its use
of resources, and the lifestyle to which it is fitted
• Describes the place and function of an organism within
the ecosystem
• Takes into account all aspects of an organism’s
existence
• The “way of life of an organism”
• Habitat
– Part of an organism’s niche, the place where the organism
lives
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Ecological Niches
• Niches can be expressed as:
– Fundamental niche—the potential, idealized niche
– Realized niche—the actual niche an organism occupies
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Resource Partitioning
• One way species avoid or reduce niche overlap
• Serves to reduce competition for resources
• Can include timing of feeding, nest sites, and
location of feeding
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Resource Partitioning
Resource partitioning of five warbler species
Each species spends most of their time feeding in different areas of the tree
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Interactions Among Organisms
• Organisms of an ecosystem interact and form
associations
• Three main types of interactions occur between
species in an ecosystem
– Symbiosis
– Predation
– Competition
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Symbiosis
• Symbiosis—two species
living in close association
• Symbiosis is the result of
coevolution, as seen in
this honeycreeper’s
curved bill perfectly
suited to sip nectar from
the tubular flowers of the
lobelia plant
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Symbiosis
• There are three main types of symbiosis
– Mutualism, where both organisms benefit
– Commensalism, where one benefits but the other is
unaffected—neither harmed nor helped
– Parasitism, one benefits at the expense of the other
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Symbiosis
• Mutualism – both organisms benefit from their
association
Most common in Central
America, the acacia ant gains
shelter and nutrients from the
acacia plant, in turn protecting
the plant from predators.
Photographed in Costa Rica.
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Symbiosis
• Commensalism – one
organism benefits from
the association without
either harming or helping
the second organism
Epiphytes are small plants that attach to
the branches and trunks of larger trees.
Photographed in Olympic National Park
Hoh Rainforest, Washington State.
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Symbiosis
• Parasitism – one organism (the parasite) benefits
from the other (the host) and harms the host
organism
Close-up of deer ticks on a
human fingertip. Females
of the species can transmit
Lyme disease while feeding
on human blood.
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EnviroDiscovery
Bee Colonies Under Threat
• Since 2006, major losses to bee
colonies have occurred
worldwide, referred to as
colony collapse disorder (CCD)
– CCD is the result of neonicotinoid
pesticides, pathogens, parasites,
and viruses such as Israeli acuteparalysis virus
• Bees are important pollinators
and many crops are threatened
by bee declines
Hand pollination of pear trees in China,
in a region where bee populations
have vanished
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Predation
• Predation—the consumption
of one species (prey) by
another species (predator)
– Coevolutionary “arms race”
as predators evolve to better
catch prey and prey evolve to
better escape predator
– The cheetah sprints at high
speeds to catch prey
– The goldenrod spider uses
camouflage to ambush prey
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Predation
• Avoiding predation
– Social behavior can decrease
predation, such as adult
meerkats standing guard at their
burrow, ready to alert the group
of danger
– Chemical defense in prey, such
as poison glands and bright
warning colors
– Camouflage to hide from
predators, such as this Indian
leaf butterfly
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Competition
• Competition
– The interaction among organisms that vie for the same
resources in an ecosystem, such as food or living space
– Can be complex
• Intraspecific competition
– Competition for resources between members of the same
species
• Interspecific competition
– Competition for resources between members of different
species
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Keystone Species
• Keystone species are
crucial to the maintenance
and function of an
ecosystem
– Not the most abundant
species, but have influence
on entire ecosystem
– May be the top predator in
an ecosystem
– Often affect the available
amount of food, water, or
other resources
The gray wolf is considered
a keystone species in its
ecosystem.
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Case Study: Global Climate Change:
How Does it Affect the Carbon Cycle?
• Biggest culprit in climate
change is the increasing
atmospheric CO2, which has
increased 20% in last 50 years
– Generated by burning of fossil fuels,
clearing and burning forests
• ‘Stabilization wedges’ is an
approach to reduce carbon
emissions; each ‘wedge’ would
result in a 1-billion-ton-peryear reduction by 2056
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