Ecosystems
Chapter 48
Ecosystem
An association of organisms and their
physical environment, interconnected by
ongoing flow of energy and a cycling of
materials
Modes of Nutrition
 Autotrophs
 Capture sunlight or chemical energy
 Producers
 Heterotrophs
 Extract energy from other organisms or
organic wastes
 Consumers, decomposers, detritivores
Simple
Ecosyste
m Model
energy
input from
sun
PHOTOAUTOTROPHS
(plants, other producers)
nutrient
cycling
HETEROTROPHS
(consumers, decomposers)
energy output (mainly heat)
Consumers
 Herbivores
 Carnivores
SPRING
fruits
insects
rodents,
rabbits
birds
 Parasites
 Omnivores
 Decomposers
 Detritivores
SUMMER
fruits
rodents,
rabbits
insects
birds
Seasonal variation in the diet of an
omnivore (red fox)
Trophic Levels
 All the organisms at a trophic level are
the same number of steps away from the
energy input into the system
 Producers are closest to the energy input
and are the first trophic level
Trophic Levels in Prairie
Fourth-level consumers (heterotrophs):
5th Top carnivores, parasites,
detritivores, decomposers
4th
Third-level consumers (heterotrophs):
Carnivores, parasites, detritivores,
decomposers
Second-level consumers (heterotrophs):
3rd Carnivores, parasites, detritivores,
decomposers
First-level consumers (heterotrophs):
2nd
Herbivores, parasites, detritivores,
decomposers
Primary producers (autotrophs):
1st Photoautotrophs, chemoautotrophs
Food Chain
 A straight-line
marsh hawk
upland sandpiper
sequence of who eats
whom
garter snake
 Simple food chains
cutworm
are rare in nature
plants
Tall-Grass Prairie Food Web
marsh hawk
sandpiper
crow
snake
frog
weasel
badger
coyote
spider
sparrow
earthworms, insects
vole
pocket
gopher
grasses, composites
ground
squirrel
Energy Losses
 Energy transfers are never 100 percent
efficient
 Some energy is lost at each step
 Limits the number of trophic levels in an
ecosystem
Grazing
Food Web
Detrital
Food Web
Two Types of Food Webs
Energy Input:
Energy Input:
Transfers:
Transfers:
Producers
(photosynthesizers)
Producers
(photosynthesizers)
energy
in
organic
wastes,
remains
herbivores
carnivores
decomposers
Energy
Output
energy
losses
as
metabolic
heat
& as net
export
from
ecosystem
energy
in
organic
wastes,
remains
Energy
Output
decomposers
decomposers
detritivores
detritivores
energy
losses
as
metabolic
heat
& as net
export
from
ecosystem
Figure 48.7
Page 871
Biological Magnification
A nondegradable or slowly degradable
substance becomes more and more
concentrated in the tissues of
organisms at higher trophic levels of a
food web
DDT in Food Webs
 Synthetic pesticide banned in United
States since the 1970s
 Birds that are carnivores accumulate DDT
in their tissues, produce brittle egg shells
DDT in an Estuary
(1967)
DDT Residues (ppm wet weight of whole live organism)
Ring-billed gull fledgling (Larus delawarensis)
Herring gull (Larus argentatus)
Osprey (Pandion haliaetus)
Green heron (Butorides virescens)
Atlantic needlefish (Strongylira marina)
Summer flounder (Paralychthys dentatus)
Sheepshead minnow (Cyprinodon variegatus)
Hard clam (Mercenaria mercenaria)
Marsh grass shoots (Spartina patens)
Flying insects (mostly flies)
Mud snail (Nassarius obsoletus)
Shrimps (composite of several samples)
Green alga (Cladophora gracilis)
Plankton (mostly zooplankton)
Water
75.5
18.5
13.8
3.57
2.07
1.28
0.94
0.42
0.33
0.30
0.26
0.16
0.083
0.040
0.00005
Primary Productivity
 Gross primary productivity is
ecosystem’s total rate of photosynthesis
 Net primary productivity is rate at which
producers store energy in tissues in
excess of their aerobic respiration
Primary Productivity
Varies
 Seasonal variation
 Variation by habitat
 The harsher the environment, the
slower plant growth, the lower the
primary productivity
Silver Springs Study
 Aquatic ecosystem in Florida
 Site of a long-term study of a grazing food web
decomposers,
detritivores
(bacteria,
crayfish)
5
1.5
third-level carnivores
(gar, large-mouth bass)
1.1
second-level consumers
(fishes, invertebrates)
37
first-level consumers
(herbivorous fishes,
turtles, invertebrates)
809
primary producers (algae,
eelgrass, rooted plants)
Pyramid of Energy Flow
 Primary producers trapped about 1.2
percent of the solar energy that entered the
ecosystem
 6-16% passed on to next level
21
top carnivores
decomposers + detritivores = 5,080
carnivores
herbivores
383
3,368
producers
20,810 kilocalories/square meter/year
Figure 48.11
Page 874
Incoming solar
Energy
Flow
In
energy not
1,700,000 kilocalories
harnessed:
Silver Springs1,679,190 (98.8%)
ENERGY INPUT:
20,810
(1.2%)
Energy losses as
metabolic heat &
as net export
Producers
from
To next trophic level:
ecosystem:
Energy in
organic
wastes and
remains:
4,245
3,368
13,197
Herbivores
720
383
Carnivores
90
21
Top carnivores
5
Figure 48.12
Page 874
2,265
272
16
Decomposers,
detritivores
5,060
ENERGY OUTPUT: 20,810
Total annual energy flow:
1,679,190
1,700,000 (100%)
All Heat in the End
 At each trophic level, the bulk of the
energy received from the previous level
is used in metabolism
 This energy is released as heat energy
and lost to the ecosystem
 Eventually all energy is released as heat
Biogeochemical Cycle
 The flow of a nutrient from the
environment to living organisms and
back to the environment
 Main reservoir for the nutrient is in the
environment
Three Categories
 Hydrologic cycle
 Water
 Atmospheric cycles
 Nitrogen and carbon
 Sedimentary cycles
 Phosphorus and sulfur
Hydrologic Cycle
Atmosphere
wind-driven water vapor
40,000
evaporation precipitation
from ocean into ocean
425,000
385,000
precipitation
onto land
111,000
evaporation from land
plants (evapotranspiration)
71,000
surface and
groundwater
flow 40,000
Ocean
Land
Figure 48.14
Page 876
Hubbard Brook
Experiment
 A watershed was experimentally stripped
of vegetation
 All surface water draining from watershed
was measured
 Removal of vegetation caused a six-fold
increase in the calcium content of the
runoff water
Hubbard Brook
Experiment
losses from
disturbed watershed
time of
deforestation
losses from
undisturbed watershed
Figure 48.15
Page 877
Carbon Cycle
 Carbon moves through the atmosphere
and food webs on its way to and from
the ocean, sediments, and rocks
 Sediments and rocks are the main
reservoir
diffusion between
atmosphere and ocean
bicarbonate and
carbonate in
ocean water
photosynthesis
combustion of fossil fuels
aerobic
respiration
marine food
webs
death,
incorporation sedimentation
into sediments
uplifting
sedimentation
marine sediments
Carbon Cycle - Marine
Figure 48.16
Page 878
atmosphere
combustion of
fossil fuels
volcanic action
terrestrial
rocks
weathering
photosynthesis
aerobic combustion
respiration of wood
sedimentation
land food
webs
soil water
leaching,
runoff
death, burial,
compaction over
geologic time
Carbon Cycle - Land
peat,
fossil
fuels
Figure 48.16
Page 878
Carbon in the Oceans
 Most carbon in the ocean is dissolved
carbonate and bicarbonate
 Ocean currents carry dissolved carbon
Carbon in Atmosphere
 Atmospheric carbon is mainly carbon
dioxide
 Carbon dioxide is added to atmosphere
 Aerobic respiration, volcanic action,
burning fossil fuels
 Removed by photosynthesis
Greenhouse Effect
 Greenhouse gases impede the escape
of heat from Earth’s surface
Figure 48.18, Page 880
Global Warming
Long-term increase in the temperature
of Earth’s lower atmosphere
Figure 48.19, Page 881
Carbon Dioxide Increase
 Carbon dioxide levels fluctuate
seasonally
 The average level is steadily increasing
 Burning of fossil fuels and deforestation
are contributing to the increase
Other Greenhouse Gases
 CFCs - synthetic gases used in plastics
and in refrigeration
 Methane - produced by termites and
bacteria
 Nitrous oxide - released by bacteria,
fertilizers, and animal wastes
Nitrogen Cycle
 Nitrogen is used in amino acids and
nucleic acids
 Main reservoir is nitrogen gas in the
atmosphere
Nitrogen Cycle
gaseous nitrogen (N2)
in atmosphere
nitrogen fixation
by industry
food webs
on land
uptake by excretion, death, uptake by
fertilizers autotrophs decomposition autotrophs
nitrogen
fixation
NH3-,NH4+
in soil
leaching
nitrogenous
wastes, remains
NO3in soil
dentrification
ammonification 2. Nitrification
1. Nitrification
NO2in soil
leaching
Figure 48.21
Page 882
Nitrogen Fixation
 Plants cannot use nitrogen gas
 Nitrogen-fixing bacteria convert
nitrogen gas into ammonia (NH3)
 Ammonia and ammonium can be
taken up by plants
Ammonification &
Nitrification
 Bacteria and fungi carry out
ammonification
 conversion of nitrogenous wastes to ammonia
 Nitrifying bacteria convert ammonium to
nitrites and nitrates
Nitrogen Loss
 Nitrogen is often a limiting factor in
ecosystems
 Nitrogen is lost from soils via leaching
and runoff
 Denitrifying bacteria convert nitrates and
nitrites to nitrogen gas
Human Effects
 Humans increase rate of nitrogen loss by
clearing forests and grasslands
 Humans increase nitrogen in water and
air by using fertilizers and by burning
fossil fuels
 Too much or too little nitrogen can
compromise plant health
Phosphorus Cycle
 Phosphorus is part of phospholipids and
all nucleotides
 It is the most prevalent limiting factor in
ecosystems
 Main reservoir is Earth’s crust; no
gaseous phase
Phosphorus Cycle
mining
FERTILIZER
GUANO
excretion
agriculture
uptake
by
autotrophs
MARINE
FOOD
WEBS
weathering
DISSOLVED
IN OCEAN
WATER
uptake
by
autotrophs
weathering
DISSOLVED IN
SOILWATER,
LAKES, RIVERS
death,
decomposition
sedimentation
LAND
FOOD
WEBS
death,
decomposition
settling
out
leaching, runoff
uplifting
TERRESTRIAL ROCKS
MARINE SEDIMENTS
over geologic time
Figure 48.23, Page 884
Human Effects
 In tropical countries, clearing lands for
agriculture may deplete phosphorus-
poor soils
 In developed countries, phosphorus
runoff is causing eutrophication of
waterways