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© 2017 Cengage Learning. All Rights Reserved.
Environmental Science, 1e SUSTAINING YOUR WORLD
G. TYLER MILLER | SCOTT E. SPOOLMAN
3Ecosystem
Dynamics
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• Cover only 7% of the earth’s land surface, but
contain half of the world’s terrestrial plant and
animal species
• Human activities have destroyed or disturbed
more than half of Earth’s tropical rain forest.
– Impacts: biodiversity loss, accelerated
atmospheric warming, changing weather patterns
• How are your local ecosystems unique, and
what challenges do they face?
Case Study: Disappearing Tropical
Rain Forests
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• Earth’s life-support system has four spherical
components that interact with each other
(geosphere, atmosphere, hydrosphere,
biosphere).
• Life is sustained by the cycling of nutrients
and energy between and through these
systems.
3.1 What Are Earth’s Major Spheres, and
How Do They Support Life?
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Earth’s Four Life-Support Systems
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• Composed of a hot core, a thick, mostly rocky
mantle, and a thin outer crust
• Gives planet the mass it needs to keep
atmosphere from escaping into space
• Contains nutrients, nonrenewable fossil fuels
(coal, oil, natural gas), mineral resources
Geosphere
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• Envelope of gases surrounding Earth
– Shields planet from meteors, blocks most harmful
UV radiation
– Helps regulate Earth’s climates
– Five layers, from bottom to top:
• Troposphere (life, weather events)
• Stratosphere (ozone layer)
• Mesosphere
• Thermosphere
• Exosphere
Atmosphere
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• Includes all of the gaseous, liquid, and solid
water on/near Earth’s surface
– Glaciers, lakes, rivers, aquifers, water vapor,
clouds, oceans
• Oceans contain about 96.5% of total water
supply, cover 71% of surface
• Less than 3% available as fresh water, most
of it frozen in ice caps, glaciers
Hydrosphere
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• Very thin layer of air, water, soil, organisms
• Consists of the parts of the atmosphere,
hydrosphere, and geosphere where life exists
Biosphere
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• Greenhouse effect
– Solar energy warms troposphere as it reflects
from Earth’s surface, interacts with CO2, CH4,
water vapor, other greenhouse gases
– Without it, Earth too cold to support life
• Air and water purification
– Living organisms (plants, animals,
microorganisms) absorb/filter pollutants from air,
water, soil
– Evaporation filters out water impurities
Earth’s Spheres Interact
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• Ecology: organisms interact with each other
and with their nonliving environment
• Ecosystems are composed of energy,
chemicals, and organisms.
• Scientists classify matter into levels of
organization ranging from molecules to
galaxies.
– Ecologists study interactions within and among
several of these levels.
3.2 What Are the Major Components of an
Ecosystem?
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Levels of the Organization of Matter in
Nature
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• Biotic (living) and abiotic (nonliving)
components of the environment
– Biotic components: plants, animals, microbes, all
other organisms
• Trophic (feeding) level: depends on whether organism
makes food (producer) or finds food (consumer), and
what its feeding behavior is if it’s a consumer
– Abiotic components: water, air, rocks, nutrients,
thermal energy, sunlight
Ecosystems Have Several Important
Components
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Living (Biotic) and Nonliving (Abiotic)
Components
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• Producers (plants) use photosynthesis to
make nutrients.
– 6 CO2 + 6 H2O + light energy → C6H6 + 6 O2
• Consumers feed on other organisms or their
remains to obtain energy.
– Herbivores (plant eaters), carnivores (meat
eaters), or omnivores (eat both plants and meat)
– Primary (eat mostly green plans or algae),
secondary (eat primary consumers), or tertiary
(eat both primary/secondary consumers)
Producers and Consumers
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• Decomposers: consumers that get their
nutrients by breaking down (decomposing)
nonliving organic matter (leaf litter, fallen
trees, dead animals)
• Detritivores: get nourishment by feeding on
detritus, or freshly dead organisms, before
they are fully decomposed
• Decomposers and detritivores are key to
nutrient cycling.
Decomposers and Detritivores
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Decomposers and Detritivores Aid
Nutrient Cycling
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The Main Components of an Ecosystem
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• Release of chemical energy stored in glucose
and other organic compounds
• Aerobic respiration: uses oxygen and glucose,
opposite of photosynthesis
– C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy
• Anaerobic respiration (fermentation): carried
out in absence of oxygen
– By-products: methane, ethyl alcohol, acetic acid,
hydrogen sulfide
Cellular Respiration
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• Energy flows through ecosystems via
movement between trophic levels through
food chains and food webs.
– The quality of energy available to organisms
decreases as each successive trophic level is
reached, because so much energy (heat) is lost
moving from one level to the next.
3.3 What Happens To Energy in an
Ecosystem?
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• Food chains
– A sequence of organisms, each of which serves
as a nutritional source for the next
– About 90% energy lost at each link in food chain,
as organisms convert chemical energy from food
to energy needed to live and grow
• Food webs
– A complex network of interconnected food chains
Energy Flows Through Ecosystems in
Food Chains and Food Webs
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Energy Flow in a Food Chain
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Feeding Relationships in a Food Web
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A Generalized Pyramid of Energy Flow
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• Gross primary productivity (GPP)
– Rate at which an ecosystem’s producers convert
radiant energy into chemical energy
• Net primary productivity (NPP)
– Rate at which producers use photosynthesis to
produce and store chemical energy, minus the
rate at which they use energy for cellular
respiration
• A measure of the rate at which producers make
chemical energy potentially available to consumers
Primary Productivity
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• Despite low NPP, oceans produce most of the
world’s biomass because of their vast size.
• Tropical rain forests have high NPP due to
their great variety and abundance of plants.
• Only plant matter represented by NPP is
available as nutrients for consumers.
– The planet’s NPP ultimately limits the number of
consumers that can survive.
Ecosystems Vary in Their Net Primary
Productivity (NPP)
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• Elements and compounds that make up
nutrients move continually through air, water,
soil, rocks, and living organisms within
ecosystems via nutrient cycles.
3.4 What Happens To Matter in an
Ecosystem?
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• Nutrient cycles, or biogeochemical cycles, are
driven directly or indirectly by incoming solar
radiation and Earth’s gravity.
– Nutrient cycles include the hydrologic (water),
carbon, nitrogen, and phosphorous cycles.
– Human activities are disrupting these cycles.
– Certain nutrients may accumulate in temporary
reservoirs, including the atmosphere, the oceans
and other bodies of water, underground deposits,
and living organisms.
Nutrients Cycle Within and Among
Ecosystems
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• The hydrologic cycle collects, purifies, and
distributes Earth’s fixed supply of water.
• Incoming solar radiation causes evaporation
(conversion of liquid water to water vapor).
– Most water vapor rises into the atmosphere,
condenses in clouds
– 90% water vapor above land contributed by
transpiration (evaporation from plant surfaces)
• Gravity draws water back to Earth as
precipitation (rain, snow, sleet).
The Hydrologic Cycle—Evaporation and
Precipitation
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• Most precipitation falling on land ecosystems
becomes surface runoff.
– Flows over land into streams, rivers, lakes,
wetlands, the ocean, where it can evaporate
• Some precipitation seeps into the soil.
– May evaporate or be used by plants, organisms
– May seep deeper into soil as groundwater that
collects in aquifers (underground layers of sand,
gravel, water-bearing rock)
The Hydrologic Cycle—Surface Runoff and
Groundwater
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The Hydrologic Cycle
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• By draining and filling in wetlands, which
disturbs natural flood control
• By withdrawing freshwater resources faster
than natural processes replenish it (aquifer
depletion, reduced river flow)
• By replacing forests/vegetation with urban
development—reducing infiltration and
increasing runoff
How Do Humans Alter the Water Cycle?
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• Carbon dioxide gas, a key component of the
carbon cycle, significantly affects global
temperatures (due to the greenhouse effect).
• How does carbon cycle through the
biosphere?
– Photosynthesis by producers
– Aerobic respiration by producers, consumers, and
decomposers
– Marine sediments (Earth’s largest store of carbon)
The Carbon Cycle
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The Global Carbon Cycle
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• By adding large amounts of carbon dioxide to
the atmosphere
– Extracting and burning fossil fuels at a much
higher rate than they are naturally formed
• By clear-cutting forests faster than they re-
grow
– Destroys carbon-absorbing vegetation
How Do Humans Alter the Carbon Cycle?
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• Atmospheric nitrogen cannot be absorbed
and used directly by organisms.
– Bacterial action makes nitrate ions available to
plants.
• Plant roots take up nitrate ions
• Animals eat plants, get nitrogen-containing compounds
• Organisms return nitrogen-rich organic compounds to
environment via waste, cast-off particles, dead remains
• Bacteria break down organic material, which eventually
releases nitrogen gas back to atmosphere
The Nitrogen Cycle
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The Nitrogen Cycle
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• By burning fossil fuels that add nitric oxide to
the atmosphere
– Nitric oxide can be converted to nitrogen dioxide
gas and nitric acid vapor, which fall as acid rain.
• By removing atmospheric nitrogen to make
fertilizer
– Excess nitrates in runoff from farm fields and
sewage discharge contaminate bodies of water
and cause excessive algal growth.
How Do Humans Alter the Nitrogen Cycle?
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• Phosphorus cycles through soils, rocks, water
and plants, but not through the atmosphere.
– Water flows over rock, eroding inorganic
compounds containing phosphate ions
– Phosphate ions wash into soil, are absorbed by
producers
– Phosphate compounds transfer from producers to
consumers
– May wash into oceans, get trapped in marine
sediments for millions of years
The Phosphorus Cycle
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The Phosphorus Cycle
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• By mining phosphorus deposits to make
fertilizer
• By clearing tropical forests, which increases
erosion and reduces phosphorus in topsoil
• By adding large quantities of phosphate ions
to streams, lakes, and oceans as a result of
fertilizer runoff and topsoil erosion
– Excess phosphates stimulate algal growth
How Do Humans Alter the Phosphorus
Cycle?
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• Scientists learn about ecosystems by:
– Using field and laboratory research
– Designing controlled experiments
– Developing mathematical and statistical models
3.5 How Do Scientists Study Ecosystems?
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• Make direct observations and take samples,
measurements of ecosystems in the field
• Carry out controlled experiments
• Use satellites, aircraft, drones equipped with
cameras
• Use GIS software to collect/analyze data
• Use radio transmitters and GPS to track
organisms
Ecologists Study Ecosystems Directly
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• Ecologists conduct research in laboratories.
– Use culture tubes, aquariums, greenhouses,
indoor/outdoor chambers with controlled variables
(light, temperature, etc.)
– Pros: allow for control of variables, study of
cause-and-effect relationships
– Cons: experiments may not reflect what actually
takes place in real ecosystem
• Mathematical modeling for large, complex
systems with many variables/large data sets
Ecologists Study Ecosystems Indirectly