Ecosystems

1
Ecosystems

• Chapter 48

2
Ecosystem

• An association of organisms and their physical
  environment, interconnected by ongoing flow of
  energy and a cycling of materials

3
Modes of Nutrition

• Autotrophs
• Capture sunlight or chemical energy
• Producers
• Heterotrophs
• Extract energy from other organisms or organic
  wastes
• Consumers, decomposers, detritivores

4
Simple Ecosystem Model
energy input from sun
PHOTOAUTOTROPHS (plants, other producers)
nutrient cycling
HETEROTROPHS (consumers, decomposers)
energy output (mainly heat)
5
Consumers

• Herbivores
• Carnivores
• Parasites
• Omnivores
• Decomposers
• Detritivores

fruits
insects
rodents, rabbits
birds
SUMMER
fruits
rodents, rabbits
insects
birds
Seasonal variation in the diet of an omnivore
(red fox)
6
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

7
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
8
Food Chain
marsh hawk

• A straight-line sequence of who eats whom
• Simple food chains are rare in nature

upland sandpiper
garter snake
cutworm
plants
9
Tall-Grass Prairie Food Web
marsh hawk
sandpiper
crow
snake
frog
coyote
badger
weasel
spider
sparrow
pocket gopher
ground squirrel
vole
earthworms, insects
grasses, composites
10
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

11
Two Types of Food Webs
Grazing Food Web
Detrital Food Web
Energy Input
Energy Input
Transfers
Transfers
Producers (photosynthesizers)
Producers (photosynthesizers)

energy losses as metabolic heat as net export
from ecosystem
energy in organic wastes, remains
energy in organic wastes, remains
energy losses as metabolic heat as net export
from ecosystem
herbivores
decomposers
decomposers
carnivores
detritivores
detritivores
decomposers
Energy Output
Energy Output
Figure 48.7 Page 871 
12
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

13
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

14
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
15
Primary Productivity

• Gross primary productivity is ecosystems total
  rate of photosynthesis
• Net primary productivity is rate at which
  producers store energy in tissues in excess of
  their aerobic respiration

16
Primary Productivity Varies

• Seasonal variation
• Variation by habitat
• The harsher the environment, the slower plant
  growth, the lower the primary productivity

17
Silver Springs Study

• Aquatic ecosystem in Florida
• Site of a long-term study of a grazing food web

third-level carnivores (gar, large-mouth bass)
1.5
second-level consumers (fishes, invertebrates)
1.1
decomposers, detritivores (bacteria, crayfish)
first-level consumers (herbivorous
fishes, turtles, invertebrates)
37
primary producers (algae, eelgrass, rooted plants)
809
5
18
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

decomposers detritivores 5,080
21
top carnivores
carnivores
383
herbivores
3,368
20,810 kilocalories/square meter/year
producers
Figure 48.11 Page 874
19
Energy Flow In Silver Springs
20,810 1,679,190
Figure 48.12 Page 874
20
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

21
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

22
Three Categories

• Hydrologic cycle
• Water
• Atmospheric cycles
• Nitrogen and carbon
• Sedimentary cycles
• Phosphorus and sulfur

23
Hydrologic Cycle
Atmosphere
precipitation onto land 111,000
wind-driven water vapor 40,000
evaporation from land plants (evapotranspiration)
71,000
evaporation from ocean 425,000
precipitation into ocean 385,000
surface and groundwater flow 40,000
Land
Ocean
Figure 48.14 Page 876
24
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

25
Hubbard Brook Experiment
losses from disturbed watershed
time of deforestation
losses from undisturbed watershed
Figure 48.15 Page 877
26
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

27
Carbon Cycle - Marine
diffusion between atmosphere and ocean
combustion of fossil fuels
bicarbonate and carbonate in ocean water
aerobic respiration
photosynthesis
marine food webs
death, sedimentation
incorporation into sediments
uplifting
sedimentation
marine sediments
Figure 48.16  Page 878
28
Carbon Cycle - Land
atmosphere
combustion of fossil fuels
volcanic action
aerobic respiration
combustion of wood
photosynthesis
terrestrial rocks
sedimentation
weathering
land food webs
soil water
peat, fossil fuels
death, burial, compaction over geologic time
leaching, runoff
Figure 48.16  Page 878
29
Carbon in the Oceans

• Most carbon in the ocean is dissolved carbonate
  and bicarbonate
• Ocean currents carry dissolved carbon

30
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

31
Greenhouse Effect

• Greenhouse gases impede the escape of heat from
  Earths surface

Figure 48.18, Page 880
32
Global Warming

• Long-term increase in the temperature of Earths
  lower atmosphere

Figure 48.19, Page 881
33
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

34
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

35
Nitrogen Cycle

• Nitrogen is used in amino acids and nucleic acids
• Main reservoir is nitrogen gas in the atmosphere

36
Nitrogen Cycle
gaseous nitrogen (N2) in atmosphere
nitrogen fixation by industry
food webs on land
uptake by autotrophs
excretion, death, decomposition
uptake by autotrophs
fertilizers
NO3- in soil
nitrogenous wastes, remains
nitrogen fixation
dentrification
ammonification
2. Nitrification
NH3-,NH4 in soil
NO2- in soil
1. Nitrification
leaching
leaching
Figure 48.21 Page 882
37
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

38
Ammonification Nitrification

• Bacteria and fungi carry out ammonification
• conversion of nitrogenous wastes to ammonia
• Nitrifying bacteria convert ammonium to nitrites
  and nitrates

39
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

40
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

41
Phosphorus Cycle

• Phosphorus is part of phospholipids and all
  nucleotides
• It is the most prevalent limiting factor in
  ecosystems
• Main reservoir is Earths crust no gaseous phase

42
Phosphorus Cycle
Figure 48.23, Page 884
43
Human Effects

• In tropical countries, clearing lands for
  agriculture may deplete phosphorus-poor soils
• In developed countries, phosphorus runoff is
  causing eutrophication of waterways