Ecosystems
Chapter 48
Ecosystems
Open systems through which energy flows and
materials are recycled
Require energy and nutrient input and generate
energy and nutrient output
Modes of Nutrition
Autotrophs
Capture sunlight or chemical energy
Producers
Heterotrophs
Extract energy from other organisms or organic
wastes
Consumers, decomposers, detritivores
Simple
Ecosystem energy
input from
sun
Model
PHOTOAUTOTROPHS
(plants, other producers)
nutrient
cycling
HETEROTROPHS
(consumers, decomposers)
energy output (mainly heat)
Consumers
Herbivores
Carnivores fruits SPRING
insects
rodents,
Parasites rabbits
birds
Omnivores
fruits SUMMER
Decomposers rodents,
rabbits insects
Fungi, bacteria birds
Detritivores Seasonal variation in the diet of an
omnivore (red fox)
Small invertebrates
Trophic Levels
Who Eats Whom?
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
Third-level consumers (heterotrophs):
4th 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 marsh hawk
A straight-line sequence
upland sandpiper
of who eats whom
Simple food chains are garter snake
rare in nature
cutworm
plants
Tall-Grass Prairie Food Web
marsh hawk
sandpiper crow
snake
frog
weasel badger coyote
spider
sparrow
vole pocket ground
earthworms, insects gopher squirrel
grasses, composites
Energy Losses
Energy transfers are never 100 percent efficient
Some energy is lost at each step
How?
Heat
Limits the number of trophic levels in an ecosystem
Grazing Detrital
Food Web Food Web
Webs
Two Types of Food Energy Input:
Energy Input:
Transfers: Transfers:
Producers Producers
(photosynthesizers) (photosynthesizers)
energy
energy energy energy losses
in herbivores losses in decomposers
decomposers as
organic as organic metabolic
metabolic heat
wastes, wastes,
heat & as net
remains carnivores & as net
remains detritivores
detritivores export
export from
from ecosystem
ecosystem
decomposers
Energy Energy Figure 48.7
Output Output
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
Effective chemical for killing mosquitoes
Accumulates in fatty tissues
Synthetic pesticide banned in United States
since the 1970s
Still persist in sediments
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) 75.5
Herring gull (Larus argentatus) 18.5
Osprey (Pandion haliaetus) 13.8
Green heron (Butorides virescens) 3.57
Atlantic needlefish (Strongylira marina) 2.07
Summer flounder (Paralychthys dentatus) 1.28
Sheepshead minnow (Cyprinodon variegatus) 0.94
Hard clam (Mercenaria mercenaria) 0.42
Marsh grass shoots (Spartina patens) 0.33
Flying insects (mostly flies) 0.30
Mud snail (Nassarius obsoletus) 0.26
Shrimps (composite of several samples) 0.16
Green alga (Cladophora gracilis) 0.083
Plankton (mostly zooplankton) 0.040
Water 0.00005
Primary Productivity
Gross primary productivity is ecosystem’s total rate of
photosynthesis for the ecosystem during an interval
Net primary productivity is rate at which producers store energy
in tissues in excess of their aerobic respiration
NPP accounts for the organic mass of plants (growth) and represents storage of
chemical energy available to consumers.
NPP = GPP - Respiration
Primary Productivity Varies
Seasonal variation
Variation by habitat
The harsher the environment, the
slower plant growth, the lower the
primary productivity
Ecological Pyramids
Biomass Pyramid
has tiers symbolizing the total dry weight of all
organisms in an ecosystem's levels at any given
time.
Biomass represents chemical energy stored in the
organic matter of a trophic level.
Most narrow sharply from producers at the base to
top-level carnivores at the top.
Silver Springs Study
Aquatic ecosystem in Florida
Site of a long-term study of a grazing food web
g/m2
third-level carnivores
1.5 (gar, large-mouth bass)
1.1 second-level consumers
decomposers,
(fishes, invertebrates)
detritivores
(bacteria, first-level consumers
crayfish) 37 (herbivorous fishes,
turtles, invertebrates)
809 primary producers (algae,
5 eelgrass, rooted plants)
Energy Pyramid
Reflects trophic structure most accurately because it
is based on energy looses at each level
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 (10%)
top carnivores 21 decomposers + detritivores = 5,080
carnivores
383
herbivores
3,368
producers 20,810 kilocalories/square meter/year
Figure 48.11
Page 874
ENERGY INPUT:
Energy Flow In
1,700,000 kilocalories
Incoming solar
energy not
Silver Springs
harnessed:
1,679,190 (98.8%)
20,810 Energy losses as
(1.2%) metabolic heat &
Energy in
Producers as net export
organic
from
wastes and To next trophic level:
ecosystem:
remains:
3,368
4,245 13,197
Herbivores
383
720 2,265
Carnivores
21 272
90 Top carnivores
5 Decomposers, 16
detritivores 5,060
Figure 48.12 ENERGY OUTPUT: 20,810 1,679,190
Page 874 Total annual energy flow: 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
Influence the availability of essential elements
in ecosystems
The amount of nutrients cycling is greater
than those entering or leaving
Main reservoir for the nutrient is in the
environment
Environmental Inputs Environmental Outputs
of Nutrients of Nutrients
Precipitation Runoff
Metabolism Evaporation
Weathering
Three Categories
Hydrologic cycle
Water
Atmospheric cycles
Nitrogen and carbon
Sedimentary cycles
Phosphorus and sulfur
Hydrologic Cycle
Atmosphere
wind-driven water vapor precipitation
40,000 onto land
111,000
evaporation precipitation evaporation from land
from ocean into ocean plants (evapotranspiration)
425,000 385,000 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 combustion of fossil fuels
carbonate in
ocean water
photosynthesis aerobic
respiration
marine food
webs
death,
incorporation sedimentation
into sediments uplifting
sedimentation
marine sediments
Carbon Cycle - Marine Figure 48.16
Page 878
atmosphere
volcanic action combustion of
fossil fuels
photosynthesis aerobic combustion
terrestrial respiration of wood
rocks
sedimentation
weathering land food
webs
soil water
peat,
death, burial, fossil
leaching, compaction over fuels
runoff geologic time
Carbon Cycle - Land 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
nitrogenous NO3-
nitrogen wastes, remains in soil dentrification
fixation
NH3-,NH4+ ammonification 2. Nitrification
in soil
leaching 1. Nitrification NO2- leaching
in soil 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
excretion GUANO
agriculture
uptake weathering uptake
by by
autotrophs autotrophs
weathering
MARINE DISSOLVED DISSOLVED IN LAND
FOOD IN OCEAN SOILWATER, FOOD
WEBS WATER LAKES, RIVERS WEBS
death, death,
decomposition decomposition
settling
sedimentation out leaching, runoff
uplifting
MARINE SEDIMENTS TERRESTRIAL ROCKS
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