Download Ecosystems - Linn-Benton Community College

BI 101 Food webs and Ecosystems
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Learning objectives
• Describe the flow of energy through the
ecosystem, and understand how this
affects the biomass of tropic levels
• Understand the cycling of nutrients such
as carbon and water
• Recognize how impacts to the nutrient
cycles affect the whole community
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Levels of study in Ecology
Organism
Population
√
Community
√
Ecosystem
Biosphere
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What is an ecosystem?
Figure 28-4b A simple marine food chain
phytoplankton
zooplankton
secondary consumer
(3rd trophic level)
producer
(1st trophic level)
primary consumer
(2nd trophic level)
tertiary consumer
(4th trophic level)
quaternary consumer
(5th trophic level)
(b) A simple marine food chain
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Figure 28-5 A simplified grassland food web
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Primary producers—the autotrophs
• Auto = self + trophy = nourishment
• Organisms take nourishment directly from
the environment
Phytoplankton—ocean
http://www.njscuba.
net/biology/eco_wat
er.html
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Terrestrial plants
http://www.100m
ag.com/know00
2.html
Consumers—heterotrophs
• Hetero = other + trophy = nourishment
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McGraw-Hill
Companies, Inc. Permission required for reproduction or display.
consumer
Trophic levels
within an
ecosystem
Detrivores (also
known as scavengers)
are special consumers
that eat dead
organisms
Decomposers are
organism that break
down organic
substances, making
them available to other
organisms
bacteria and fungi are
the principal
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Sun
Trophic
level 4
Top
carnivore
Secondary consumer
Trophic
level 3
Carnivore
Primary consumer
Trophic
level 2
Herbivore
Producer
Trophic
level 1
Decomposers
Fungi
Bacteria
8
Detrital food web
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Energy pathways in ecosystems
• All ecosystems need energy so its living
members can grow and reproduce
• Source of energy = the sun
• One-way path
• Flows through various organisms, and
eventually dissipates into the environment
as heat
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Energy Flows Through
Ecosystems
How heterotrophs use (and
lose) food energy
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17%
Growth
33%
Cellular
respiration
50%
Feces
Much of the energy captured by plants is lost as
energy passes through the ecosystem
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Algae and
cyanobacteria
Energy loss in
an ecosystem
Small
heterotrophs
Trout
Smelt
Human
1.2 calories
6 calories
1000 calories
150 calories
30 calories
12
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Food Supply – Energy Pyramid
Energy is used much more efficiently if humans eat plants
(first tropic level) instead of meat (second tropic level). A given
area of farmland can support more people if the crops are fed
directly to people rather than to livestock that people then eat.
For example if a man needs 3,000 Calories per day, then
30,000 Cal beef are needed, which in turn need 300,000 Cal of
corn. This works out to be 1.5 acres of corn per day per
person. If the person ate corn directly then 10 people could be
supported by the same 1.5 acres of corn.
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Biogeochemical Cycles
• In contrast to the one-way flow of energy,
materials (such as water, carbon and
nitrogen) cycle through ecosystems.
– Water cycle
– Carbon cycle
– Nitrogen cycle
– Phosphorus cycle
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Figure 28-7 The hydrologic cycle
reservoirs
processes
water vapor in
the atmosphere
precipitation
over land
precipitation
over the ocean
evaporation
from land and
transpiration
from plants
evaporation
from the
ocean
evaporation from
lakes and rivers
lakes and rivers
seepage into soil
groundwater,
including
aquifers
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runoff
from rivers
and land
extraction for
agriculture
water in
the ocean
Burning or clear-cutting forests breaks the
water cycle
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Figure 28-8 The carbon cycle
reservoirs
CO2 in the
atmosphere
processes
trophic levels
burning
fossil fuels
CO2 dissolved
in the ocean
respiration
fire
photosynthesis
producers
consumers
detritus feeders
and decomposers
decomposition
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fossil fuels
(coal, oil, natural gas)
Figure 28-14 Greenhouse gases and global warming
5 Most heat is radiated
back into space
Sun
1 Sunlight energy
enters the atmosphere
6 Some atmospheric heat is
retained by greenhouse gases
2 Some energy
is reflected back
into space
volcanoes
3 Most sunlight strikes
Earth’s surface and is
converted into heat
vehicle
emissions
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4 Heat is
radiated back into
the atmosphere
agricultural
activities
forest
fires
power plants
and factories
homes and
buildings
Figure 28-15 Global warming parallels atmospheric
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Figure 28-9 The nitrogen cycle
reservoirs
N2 in the
atmosphere
processes
trophic levels
burning
fossil fuels
lightning
application of
manufactured fertilizer
consumers
ammonia and
nitrates in water
producers
uptake by
producers
detritus feeders
and decomposers
nitrogen-fixing
bacteria in soil
and legume roots
decomposition
denitrifying
bacteria
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ammonia
and nitrates
in soil
Figure 28-10 The phosphorus cycle
reservoirs
processes
trophic levels
phosphate
in rock
geological
uplift
application of
manufactured
fertilizer
runoff
from rivers
consumers
producers
detritus feeders
and decomposers
decomposition
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runoff from
fertilized
fields
uptake by
producers
phosphate
in water
phosphate
in soil
phosphate
in sediment
formation of
phosphate-containing
rock