Chapter 24
Lecture Outline
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Global Ecology and
Human Interferences
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Points to ponder
• What is an ecosystem and what are its biotic
components?
• What are energy flow and chemical cycling in
an ecosystem?
• What are the two major ecosystems on
earth?
• Describe the three types of terrestrial
ecosystems and the two types of aquatic
ecosystems.
• Compare and contrast food webs and food
pyramids.
• What is a biogeochemical cycle?
• What is a reservoir and an exchange pool?
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Points to ponder
• Explain the water, carbon, nitrogen, and
phosphorus cycles.
• What human activities interfere with these
cycles?
• What problems are we creating by altering
these pathways?
• What is biomagnification and why is mercury a
concern?
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24.1 The Nature of Ecosystems
The nature of ecosystems
•
Biosphere – the regions of the Earth’s waters,
crust, and atmosphere inhabited by living
organisms
•
Ecosystem – a place where organisms interact
with each other and their environment
–
–
Terrestrial: several distinct types based on
temperature and waterfall
Aquatic: freshwater and marine
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24.1 The Nature of Ecosystems
Terrestrial ecosystems
•
Forests – dominated by trees
•
•
•
•
Tropical rain forest
Coniferous forests (taiga)
Temperate deciduous forests
Grasslands – dominated by grass
•
•
Tropical grasslands
Temperate grasslands (prairie)
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24.1 The Nature of Ecosystems
Terrestrial ecosystems
•
Deserts – characterized by lack of
available moisture
•
•
Tundra
Deserts
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24.1 The Nature of Ecosystems
Terrestrial ecosystems
Figure 24.1 The
distribution of the
major terrestrial
biomes.
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24.1 The Nature of Ecosystems
Aquatic ecosystems
•
Marine
•
•
•
•
•
Seashores
Oceans
Coral reefs
Estuaries
Freshwater
•
•
•
•
Lakes
Ponds
Rivers
Streams
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24.1 The Nature of Ecosystems
Aquatic ecosystems
Figure 24.2 Examples of freshwater and saltwater ecosystems.
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a.
c.
b.
d.
a: © Francois Gohier/Photo Researchers; b: © The McGraw-Hill Companies, Inc. Carlyn Iverson, photographer;
c: © David Hall/Photo Researchers; d: © Vol. 121/Corbis RF
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24.1 The Nature of Ecosystems
Components of an ecosystem
•
Abiotic components – nonliving environment
•
Biotic components - living components
•
•
Autotrophs – producers
Heterotrophs – consumers
• Herbivores – feed on plants and algae
• Carnivores – feed on other animals
• Omnivores – eat both plants and animals
• Detritus feeders – feed on decomposing
organic matter
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24.1 The Nature of Ecosystems
Components of an ecosystem
•
Niche – the role an organism plays in an
ecosystem such as how it gets its food,
what it eats, and how it interacts with other
organisms
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24.1 The Nature of Ecosystems
Biotic components of an ecosystem
Figure 24.3 The biotic components of
an ecosystem.
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24.1 The Nature of Ecosystems
Energy flow and chemical cycling
•
Energy flow
• It begins and continues when producers
absorb solar energy.
• Energy flow occurs as nutrients pass from
one population to another.
• This energy is converted to heat that
dissipates into the environment.
• Only a portion of energy is passed to
organisms as they consume one another.
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24.1 The Nature of Ecosystems
Energy flow and chemical cycling
•
Chemical cycling
• Inorganic nutrients are returned to producers
from the atmosphere or soil.
• Chemicals recycle within and between
ecosystems.
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24.1 The Nature of Ecosystems
Energy flow and chemical cycling
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solar
energy
heat
producers
consumers
inorganic
nutrient pool
heat
Figure 24.4 Energy flow and
chemical cycling in an
ecosystem.
energy
heat
decomposers
nutrients
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24.1 The Nature of Ecosystems
Fate of food energy taken
in by an herbivore
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Heat to
environment
growth and reproduction
Energy to
carnivores
Energy
to detritus
feeders
Figure 24.5 The fate of
food energy taken in by an
herbivore.
© George D. Lepp/Photo Researchers, Inc.
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24.2 Energy Flow
Energy flow
•
Food web – describes who eats whom
• Grazing food web
• Detrital food web
•
Trophic levels – composed of all organisms
that feed at a particular link in the food chain
• Producers, primary consumers, and
secondary consumers
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24.2 Energy Flow
Energy flow
•
Ecological pyramid – reflects the loss of
energy from one trophic level to another
• Only about 10% of the energy of one
trophic level is available to the next
trophic level
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24.2 Energy Flow
Food webs
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Autotrophs
Herbivores/Omnivores
Carnivores
owls
nuts
birds
hawks
leaf-eating
insects
deer
foxes
leaves
chipmunks
rabbits
skunks
snakes
detritus
mice
mice
a.
death
death
Figure 24.6 Food webs
illustrate ecological
relationships.
fungi and bacteria in detritus
b.
death
invertebrates
carnivorous invertebrates
salamanders
shrews
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24.2 Energy Flow
An example of a food pyramid
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top carnivores
1.5g/m2
carnivores
11g/m2
herbivores
37g/m2
producers
809g/m2
Figure 24.7 The
influence of
trophic level on
biomass.
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24.3 Global Biogeochemical Cycles
Biogeochemical cycles
• Biogeochemical cycles are pathways by
which chemicals circulate through an
ecosystem.
1. Water cycle
2. Carbon cycle
3. Nitrogen cycle
4. Phosphorus cycle
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24.3 Global Biogeochemical Cycles
Biogeochemical cycles
• Reservoir – fossil fuels, minerals in rocks,
and sediments in oceans contain inorganic
nutrients that are limited in availability
• Exchange pools – atmosphere, soil, and
water are ready sources of inorganic
nutrients
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24.3 Global Biogeochemical Cycles
Biogeochemical cycles
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Reservoir
• fossilfuels
• mineral
in rocks
• sediment
in oceans
Exchange
Pool
• atmosphere
• soil
• water
Community
Figure 24.8
The cycling of
nutrients
between biotic
communities
and
biogeochemical
reservoirs.
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24.3 Global Biogeochemical Cycles
Water cycle
•
Water evaporates from bodies of water,
land, and plants, and returns when
water falls on land to enter the ground,
surface waters, or aquifers.
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24.3 Global Biogeochemical Cycles
Water cycle
•
Human activities that interfere
•
•
•
Withdrawing water from aquifers
Clearing vegetation from the land and
building structures that prevent
percolation and increase runoff
Adding pollutants to water such as
sewage and chemicals
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24.3 Global Biogeochemical Cycles
Water cycle
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transpiration from plants
and evaporation from soil
H2O in Atmosphere
2
precipitation
over land
transport of water vapor by wind
lake
1
evaporation
from ocean
2
precipitation
to ocean
5 fresh water runoff
6
aquifer
Ocean
I ce
4
Groundwaters
Figure 24.9 The hydrologic (water) cycle.
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24.3 Global Biogeochemical Cycles
Carbon cycle
• CO2 is exchanged between the atmosphere
and living organisms.
• Plants incorporate atmospheric CO2 into
nutrients through photosynthesis, providing
food for themselves and other organisms.
• CO2 is returned to the atmosphere through
respiration.
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24.3 Global Biogeochemical Cycles
Carbon cycle
Figure 24.10 The
carbon cycle.
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24.3 Global Biogeochemical Cycles
Carbon cycle
•
Human activities that interfere
•
Burning of fossil fuels and the destruction of
forests are adding CO2 to the atmosphere faster
than it is being removed.
•
CO2 and other gases (N2O and CH4) are being
emitted due to human activities.
•
These gases are called greenhouse gases
because they trap heat; this contributes to
global warming.
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24.3 Global Biogeochemical Cycles
Global warming and climate change
Figure 24.11 Global warming and climate change.
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24.3 Global Biogeochemical Cycles
Nitrogen cycle
•
78% of the atmosphere is nitrogen gas (N2) but
plants cannot use this form.
•
Nitrogen-fixing bacteria convert nitrogen gas to
ammonium (NH4+), which can be used by plants.
•
Nitrifying bacteria convert ammonium to nitrate
(NO3-).
•
Bacteria convert nitrate back to nitrogen gas
through a process called denitrification.
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24.3 Global Biogeochemical Cycles
Nitrogen cycle
Figure 24.12 The nitrogen cycle.
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24.3 Global Biogeochemical Cycles
Nitrogen cycle
•
Human activities that interfere
•
We add nitrogen fertilizers that run off into lakes
and streams, causing major fish kills by
eutrophication.
•
Burning of fossil fuels
- It puts nitrogen oxides and sulfur dioxide into
the atmosphere, where they combine with
water vapor to form acids that return to earth
as acid deposition.
- It results in nitrogen oxides and hydrocarbons
that react with one another to produce smog.
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24.3 Global Biogeochemical Cycles
Thermal inversions and smog
• During a thermal inversion, pollutants are
trapped near the Earth.
– The air does not circulate, so pollutants can build
up to dangerous levels.
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cooler air
cool air
warm air
a. Normal pattern
cool air
warm inversion layer
cool air
b. Thermal inversion
Figure 24.14 Thermal inversions.
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24.3 Global Biogeochemical Cycles
Nitrogen cycle
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a.
c.
b.
a: © Larry Lee Photography/Corbis RF; b: © Oxford Scientific/Photolibrary/Getty Images;
c: © Sue Baker/Photo Researchers
Figure 24.13 The effects of acid deposition.
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24.3 Global Biogeochemical Cycles
Phosphorus cycle
•
Phosphate ions
become
available to
living
organisms by
the slow
weathering of
rocks.
•
Phosphate is a
limiting nutrient
in ecosystems.
Figure 24.15 The phosphorus cycle.
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24.3 Global Biogeochemical Cycles
Phosphorus cycle
•
Human activities that interfere
•
Runoff of phosphate due to fertilizer and
discharge from sewage treatment plants
results in eutrophication.
•
Sources of water pollution
-
Point sources are the easily identifiable
sources.
Nonpoint sources cannot be specifically
identified (e.g., runoff).
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24.3 Global Biogeochemical Cycles
Biomagnification of mercury
•
•
•
•
Emissions of mercury into the environment can
lead to serious health effects for humans, fish,
and wildlife.
There is widespread mercury contamination in
streams, wetlands, reservoirs, and lakes
throughout most of the U.S.
Bioaccumulation occurs when an organism
accumulates a contaminant such as mercury
faster than it can eliminate it.
Mercury enters ecosystems at the base of the
food chain and increases in concentration as it
moves up higher trophic levels.
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24.3 Global Biogeochemical Cycles
Sources of water pollution
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Sources of Water Pollution
acidic water
from mines
sediments
Leading to Cultural Eutrophication
Oxygen-demanding
waste
Biodegradable organic compounds
(e.g., sewage, wastes from food-processing
plants, paper mills, and tanneries)
Plant nutrients
Nitrates and phosphates from detergents,
fertilizers, and sewage treatment plants
Sediments
Enriched soil in water due to soil erosion
Thermal discharges
Heated water from power plants
city
crop dusting
industrial wastes
barnyard wastes
biomedical
wastes
Health Hazards
Disease-causing agents
Synthetic organic
compounds
Bacteria and viruses from sewage and
barnyard waste (causing, for example,
cholera, food poisoning, and hepatitis)
suburban
development
Pesticides, industrial chemicals
(e.g., PCBs)
fertilizer runoff
Inorganic chemicals
and minerals
Acids from mines and air pollution;
dissolved salts; heavy metals
(e.g., mercury) from industry
Radiation
Radioactive substances from nuclear
power plants, medical and research facilities
sewage
treatment plant
oil pollution
nuclear reactor
Figure 24.16 Some sources of surface water pollution.
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