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Unformatted text preview: 4/27/09
 Lec
81.
Ecosystems
 Mark
A.
Sarvary
 Organismal
 ecology
 Population
 ecology
 Community
 ecology
 Ecosystem
 ecology
 Landscape
 ecology
 Global
 ecology
 Overview:
Observing
Ecosystems
 •  An
ecosystem
consists
of
all
the
organisms
living
 in
a
community,
as
well
as
the
abiotic
factors
 with
which
they
interact
 •  Ecosystem
dynamics
involve
two
main
 processes:
energy
flow
and
chemical
cycling
 Physical
laws
govern
energy
flow
and
 chemical
cycling
in
ecosystems
 •  Ecologists
study
the
transformations
of
energy
 and
matter
within
their
system
 •  The
first
law
of
thermodynamics
states
that
 energy
cannot
be
created
or
destroyed,
only
 transformed
(but
in
an
ecosystem,
energy
 conversions
are
not
completely
efficient)
 •  The
law
of
conservation
of
mass
states
that
 matter
cannot
be
created
or
destroyed
 Trophic
Levels
 •  heterotrophs
depend
on
the
 biosynthetic
output
of
other
 organisms
 •  Detritivores,
or
decomposers,
are
consumers
 that
derive
their
energy
from
detritus,
nonliving
 organic
matter
 •  Autotrophs
build
molecules
 themselves
using
 photosynthesis
or
 chemosynthesis
as
an
energy
 source;
 1
 4/27/09
 •  Primary
production
in
an
ecosystem
is
the
 amount
of
light
energy
converted
to
chemical
 energy
by
autotrophs
during
a
given
time
period
 Ecosystem
Energy
Budgets
 •  The
extent
of
photosynthetic
production
sets
 the
spending
limit
for
an
ecosystem’s
energy
 budget
 • Standing
crop
is
the
total
biomass
of
photosynthetic
autotrophs
 at
a
given
time
 Only
NPP
is
available
to
consumers
 
 Most
productive
 ecosystems
per
unit
 area:
 Tropical
rain
forests

 Net
primary
production
(NPP):
GPP‐energy
 used
for
respiration
 estuaries
 Gross
primary
production
(GPP):
Total
primary
 production
in
an
ecosystem

 coral
reefs
 • Standing
crop
is
the
total
biomass
of
photosynthetic
autotrophs
 at
a
given
time
 Fig.
55‐5
 TECHNIQUE
 80
 Snow
 Clouds
 Vegetation
 40
 Soil
 20
 Liquid
water
 0
 400
 600
 Visible
 800
 1,000
 1,200
 Percent
reflectance
 •  Marine
ecosystems
are
relatively
unproductive
per
unit
 area,
but
contribute
much
to
global
net
primary
 production
because
of
their
volume
 60
 Near‐infrared
 Wavelength
(nm)
 2
 4/27/09
 Fig.
55‐6
 Global
Carrying
Capacity
 Net
primary
production
(kg
carbon/m2∙yr)
 ∙ 0
 1
 2
 3
 Use
of
photosynthetic
products
 Primary
Production
in
Aquatic
 Ecosystems
 •  In
marine
and
freshwater
ecosystems,
both
light
 and
nutrients
control
primary
production
 •  Depth
of
light
penetration
affects
primary
 production
in
the
photic
zone
of
an
ocean
or
lake
 Nutrient
Limitation
 •  A
limiting
nutrient
is
the
element
that
must
be
 added
for
production
to
increase
in
an
area
 •  Nitrogen
and
phosphorous
are
typically
the
 nutrients
that
most
often
limit
marine
production
 •  Experiments
in
the
Sargasso
Sea
in
the
subtropical
 Atlantic
Ocean
showed
that
iron
limited
primary
 production
 •  Upwelling
of
nutrient‐rich
waters
in
parts
of
the
 oceans
contributes
to
regions
of
high
primary
 production
 •  In
some
areas,
sewage
runoff
has
caused
 eutrophication
of
lakes,
which
can
lead
to
loss of
most
fish
species
 3
 4/27/09
 •  In
terrestrial
ecosystems,
temperature
and
moisture
 affect
primary
production
on
a
large
scale,
and
soil
 nutrient
on
a
local
scale
 •  Actual
evapotranspiration
is
the
water
annually
 transpired
by
plants
and
evaporated
from
a
landscape
 •  Actual
evapotranspiration
can
represent
the
contrast
 between
wet
and
dry
climates
 Net
primary
production
(g/m2∙yr)
 ∙ Primary
Production
in
Terrestrial
 Ecosystems
 Fig.
55‐8
 3,000
 Tropical
forest
 2,000
 Temperate
forest
 1,000
 Desert
 shrubland
 0
 Mountain
coniferous
forest
 Temperate
grassland
 Arctic
tundra
 0
 500
 1,500
 1,000
 Actual
evapotranspiration
(mm
H2O/yr)
 Production
Efficiency •  Secondary
production
of
an
ecosystem
is
the
 amount
of
chemical
energy
in
food
converted
to
 new
biomass
during
a
given
period
of
time
 •  When
a
caterpillar
 feeds
on
a
leaf,
only
 about
one‐sixth
of
 the
leaf ’s
energy
is
 used
for
secondary
 production
 •  An
organism’s
 production
efficiency
 is
the
fraction
of
 energy
stored
in
food
 that
is
not
used
for
 respiration
 
 Trophic
Efficiency
and
Ecological
Pyramids
 •  Trophic
efficiency
is
 the
percentage
of
 production
 transferred
from
one
 trophic
level
to
the
 next
 •  It
usually
ranges
from
 5%
to
20%
 •  Trophic
efficiency
is
 multiplied
over
the
 length
of
a
food
chain
 If
trophic
efficiency
is
10%,
and
the
primary
producers
 make
10000
J
of
energy,
what
is
the
energy
level
(in
 Joules)
at
the
tertiary
consumer
level?
 A,
1
 B,
10
 C,
100
 D,
1000
 E,
10000
 4
 4/27/09
 If
trophic
efficiency
is
10%,
and
the
primary
producers
 make
10000
J
of
energy,
what
is
the
energy
level
(in
 Joules)
at
the
tertiary
consumer
level?
 A,
1
 *
B,
10
 C,
100
 D,
1000
 E,
10000
 Fig.
55‐10
 Tertiary
 consumers
 Secondary
 consumers
 Primary
 consumers
 Primary
 producers
 0.1%
of
chemical
energy
fixed
 by
photosynthesis
 10
J
 100
J
 1,000
J
 10,000
J
 1,000,000
J
of
sunlight
 Energetic
hypothesis:
inefficient
energy
transfer
 among
trophic
levels
 •  Most
terrestrial
ecosystems
have
large
standing
 crops
despite
the
large
numbers
of
herbivores
 •  Turnover
time
is
a
ratio
of
the
standing
crop
 biomass
to
production
 •  The
green
world
hypothesis
proposes
several
 factors
that
keep
herbivores
in
check:
 –  Plant
defenses
 –  Limited
availability
of
essential
nutrients
 –  Abiotic
factors
 –  Intraspecific
competition
 –  Interspecific
interactions
 Biological
and
geochemical
processes
cycle
 nutrients
between
organic
and
inorganic
 parts
of
an
ecosystem
 •  Life
depends
on
recycling
chemical
 elements
 •  Nutrient
circuits
in
ecosystems
involve
 biotic
and
abiotic
components
and
are
 often
called
biogeochemical
cycles
 5
 4/27/09
 Fig.
55‐13
 Reservoir
A
 Organic
 materials
 available
 as
nutrients
 Living
 organisms,
 detritus
 Reservoir
B
 Organic
 materials
 unavailable
 as
nutrients
 Coal,
oil,
 peat
 Fig.
55‐13
 Reservoir
A
 Organic
 materials
 available
 as
nutrients
 Living
 organisms,
 detritus
 Reservoir
B
 Organic
 materials
 unavailable
 as
nutrients
 Coal,
oil,
 peat
 Fossilization
 Fossilization
 Assimilation, photosynthesis
 Respiration,
 decomposition,
 excretion
 Burning
 of
fossil
fuels
 Reservoir
D
 Inorganic
 materials
 unavailable
 as
nutrients
 Minerals
 in
rocks
 Assimilation,
 photosynthesis
 Respiration,
 decomposition,
 excretion
 Burning
 of
fossil
fuels
 Reservoir
D
 Inorganic
 materials
 unavailable
 as
nutrients
 Minerals
 in
rocks
 Reservoir
C
 Inorganic
 materials
 available
 as
nutrients
 Atmosphere,s oil,
water
 Reservoir
C
 Inorganic
 materials
 available
 as
nutrients
 Atmosphere,s oil,
water
 Weathering,
 erosion
 Formation
of
 sedimentary
rock
 Weathering,
 erosion
 Formation
of
 sedimentary
rock
 Fig.
55‐13
 Reservoir
A
 Organic
 materials
 available
 as
nutrients
 Living
 organisms,
 detritus
 Reservoir
B
 Organic
 materials
 unavailable
 as
nutrients
 Coal,
oil,
 peat
 Fossilization
 Assimilation,
 photosynthesis
 Respiration,
 decomposition,
 excretion
 Burning
 of
fossil
fuels
 Reservoir
D
 Inorganic
 materials
 unavailable
 as
nutrients
 Minerals
 in
rocks
 Reservoir
C
 Inorganic
 materials
 available
 as
nutrients
 Atmosphere,s oil,
water
 The
Water
Cycle
 •  97%
of
the
biosphere’s
 water
is
contained
in
 the
oceans,
2%
is
in
 glaciers
and
polar
ice
 caps,
and
1%
is
in
 lakes,
rivers,
and
 groundwater
 Weathering,
 erosion
 Formation
of
 sedimentary
rock
 Fig.
55‐14b
 The
Carbon
Cycle
 •  Carbon
reservoirs
include
fossil
fuels,
soils
and
 sediments,
solutes
in
oceans,
plant
and
animal
 biomass,
and
the
atmosphere
 •  CO2
is
taken
up
and
released
through
 photosynthesis
and
respiration;
additionally,
 volcanoes
and
the
burning
of
fossil
fuels
 contribute
CO2
to
the
atmosphere
 CO2
in
atmosphere
 Photosynthesis
 Photo‐
 synthesis
 Cellular
 respiration
 Burning
of
 fossil
fuels
 Phyto‐
 and
wood
 plankton
 Higher‐level
 consumers
 Primary
 consumers
 Detritus
 Carbon
compounds
 in
water
 Decomposition
 6
 4/27/09
 The
Terrestrial
Nitrogen
 Cycle
 •  Nitrogen
is
a
component
of
 amino
acids,
proteins,
and
 nucleic
acids
 •  The
main
reservoir
of
 nitrogen
is
the
atmosphere
 (N2),
though
this
nitrogen
 must
be
converted
to
NH4+
or
 NO3–
for
uptake
by
plants,
via
 nitrogen
fixation
by
bacteria
 •  Organic
nitrogen
is
decomposed
to
NH4+
by
 ammonification,
and
NH4+
is
decomposed
to
 NO3–
by
nitrification
 •  Denitrification
converts
NO3–
back
to
N2
 Fig.
55‐14d
 The
Phosphorus
Cycle
 •  Phosphorus
is
a
major
constituent
of
nucleic
 acids,
phospholipids,
and
ATP
 •  Phosphate
(PO43–)
is
the
most
important
 inorganic
form
of
phosphorus
 •  The
largest
reservoirs
are
sedimentary
rocks
of
 marine
origin,
the
oceans,
and
organisms
 Precipitation
 Geologic
 uplift
 Weathering
 of
rocks
 Runoff
 Decomposition
 Plankton
 Dissolved
PO43–
 Uptake
 Sedimentation
 Leaching
 Soil
 Consumption
 Plant
 uptake
 of
PO43–
 Decomposition
and
Nutrient
Cycling
 Rates
 •  Decomposers
(detritivores)
play
a
key
role
in
the
 general
pattern
of
chemical
cycling
 •  The
rate
of
decomposition
is
controlled
by
 temperature,
moisture,
and
nutrient
availability
 •  Rapid
decomposition
results
in
relatively
low
 levels
of
nutrients
in
the
soil
 Fig.
55‐15
 EXPERIMENT
 Ecosystem
type
 Arctic
 Subarctic
 Boreal
 Temperate Grassland
 Mountain
 A
 G
 M T
 U
 S
 N
 H,I
 L
 B,C
 E,F
 K
 Q
 D
 O
 J
 R
 P
 RESULTS
 80
 70
 Percent
of
mass
lost
 60
 50
 40
 30
 20
 10
 0
 –15
 A
 C
 B
 E
 D
 F
 G
 K
 J
 I
 H
 R
 O
 Q
 P
 S
 N
 M L
 U
 T
 –10
 –5
 0
 5
 10
 Mean
annual
temperature
(ºC)
 15
 7
 4/27/09
 Case
Study:
Nutrient
Cycling
in
the
 Hubbard
Brook
Experimental
Forest
 •  Vegetation
strongly
regulates
nutrient
cycling
 •  The
research
team
constructed
a
dam
on
the
site
 to
monitor
loss
of
water
and
minerals
 •  In
one
experiment,
the
trees
in
one
valley
were
cut
 down,
and
the
valley
was
sprayed
with
herbicides
 Fig.
55‐16
 (a)
Concrete
dam
 





and
weir
 (b)
Clear‐cut
watershed
 Nitrate
concentration
in
runoff
 (mg/L)
 80
 60
 40
 20
 4
 3
 2
 1
 0
 Completion
of
 tree
cutting
 Deforested
 Control
 1965
 1966
 1967
 1968
 (c)
Nitrogen
in
runoff
from
watersheds
 •  Net
losses
of
water
and
minerals
were
studied
 and
found
to
be
greater
than
in
an
undisturbed
 area
 •  These
results
showed
how
human
activity
can
 affect
ecosystems
 •  As
the
human
 population
has
 grown,
our
activities
 have
disrupted
the
 trophic
structure,
 energy
flow,
and
 chemical
cycling
of
 many
ecosystems
 Agriculture
and
Nitrogen
Cycling
 •  The
quality
of
soil
varies
with
the
amount
of
 organic
material
it
contains
 •  Agriculture
removes
from
ecosystems
nutrients
 that
would
ordinarily
be
cycled
back
into
the
soil
 •  Nitrogen
is
the
main
nutrient
lost
through
 agriculture;
thus,
agriculture
greatly
affects
the
 nitrogen
cycle
 •  Industrially
produced
fertilizer
is
typically
used
 to
replace
lost
nitrogen,
but
effects
on
an
 ecosystem
can
be
harmful
 The
Green
revolution
 Contamination
of
Aquatic
Ecosystems
 •  Critical
load
for
a
nutrient
is
the
amount
that
 plants
can
absorb
without
damaging
the
 ecosystem
 • Pesticides
 • Irrigation
 • Synthetic
nitrogen
fertilizer
 • Improved
crop
varieties
 •  When
excess
nutrients
are
added
to
an
 ecosystem,
the
critical
load
is
exceeded
 •  Sewage
runoff
causes
cultural
eutrophication,
 excessive
algal
growth
that
can
greatly
harm
 freshwater
ecosystems
 8
 4/27/09
 Acid
Precipitation
 •  Combustion
of
fossil
fuels
is
the
main
cause
of
 acid
precipitation
 •  Ecosystems
downwind
from
industrial
regions
 have
been
damaged
by
rain
and
snow
 containing
nitric
and
sulfuric
acid
 •  Acid
precipitation
changes
soil
pH
and
causes
 leaching
of
calcium
and
other
nutrients
 Fig.
55‐19
 4.5
 4.4
 4.3
 pH
 4.2
 4.1
 4.0
 1960
 1965
 1970
 1975
 1980
 1985
 1990
 1995
 2000
 Year
 Concentration
of
PCBs
 •  Biological
magnification
concentrates
toxins
at
 higher
trophic
levels,
where
biomass
is
lower
 •  Many
pesticides
such
as
DDT
are
subject
to
 biological
magnification
in
ecosystems
 •  In
the
1960s
Rachel
Carson
brought
attention
to
 the
biomagnification
of
DDT
in
birds
in
her
book
 Silent
Spring
 Fig.
55‐20
 Industrial
bi‐products
 Polychlorinated
biphenyls
 PCB
were
used
as
:
 • dielectric
fluids
in
transformers
 coolants
and
lubricants,

 • stabilizing
additives
in
flexible
PVC
 coatings
of
electrical
wiring
and
 electronic
components,

 • pesticide
extenders,

 • cutting
oils,

 • flame
retardants,
 • 
hydraulic
fluids,

 • sealants
(used
in
caulking,
etc),
 adhesives
and

wood
floor
finishes
 • paints,
de‐dusting
agents,
and
in
 carbonless
copy
paper.
 Herring
 gull
eggs
 124
ppm
 Lake
trout
 4.83
ppm
 Smelt
 1.04
ppm
 Zooplankton
 0.123
ppm
 Phytoplankton
 0.025
ppm
 Greenhouse
Gases
and
Climate
change
 •  One
problem
caused
 by
human
activities
is
 the
rising
level
of
 atmospheric
carbon
 dioxide
 •  Due
to
the
burning
of
 fossil
fuels
and
other
 human
activities,
the
 concentration
of
 atmospheric
CO2
has
 been
steadily
increasing
 Fig.
55‐21
 14.9
 390
 380
 370
 CO2
concentration
(ppm)
 14.8
 14.7
 14.6
 Average
global
temperature
(ºC)
 Temperature
 14.5
 14.4
 14.3
 14.2
 CO2
 14.1
 14.0
 13.9
 13.8
 360
 350
 340
 330
 320
 310
 300
 13.7
 13.6
 1960
 1965
 1970
 1975
 1980
 1985
 Year
 1990
 1995
 2000
 2005
 9
 4/27/09
 How
Elevated
CO2
Levels
Affect
Forest
 Ecology
 •  The
FACTS‐I
experiment
is
testing
how
elevated
CO2
 influences
tree
growth,
carbon
concentration
in
soils,
 and
other
factors
over
a
ten‐year
period
 • The
CO2‐enriched
plots
produced
more
wood
than
 the
control
plots,
though
less
than
expected
 • The
availability
of
nitrogen
and
other
nutrients
 appears
to
limit
tree
growth
and
uptake
of
CO2

 The
Greenhouse
Effect
and
Climate
 •  CO2,
water
vapor,
and
other
greenhouse
gases
 reflect
infrared
radiation
back
toward
Earth;
this
 is
the
greenhouse
effect

 •  This
effect
is
important
for
keeping
Earth’s
 surface
at
a
habitable
temperature
 •  Increased
levels
of
atmospheric
CO2
are
 magnifying
the
greenhouse
effect,
which
could
 cause
climatic
change
 •  Increasing
concentration
of
atmospheric
CO2
is
 linked
to
increasing
global
temperature
 Depletion
of
Atmospheric
Ozone
 •  Life
on
Earth
is
protected
from
damaging
effects
 of
UV
radiation
by
a
protective
layer
of
ozone
 molecules
in
the
atmosphere
 •  Scientists
first
described
an
“ozone
hole”
over
 Antarctica
in
1985;
it
has
increased
in
size
as
 ozone
depletion
has
increased
 10
 4/27/09
 •  Destruction
of
atmospheric
ozone
probably
 results
from
chlorine‐releasing
pollutants
such
 as
CFCs
produced
by
human
activity
 Have
a
warm
day!
 11
 ...
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This note was uploaded on 10/20/2009 for the course BIO G 1102 taught by Professor Walcott during the Spring '08 term at Cornell University (Engineering School).

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