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 Heterotrophs
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
SPRING
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 A straight-line sequence of who eats whom
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
weasel
badger
coyote
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 losses
as metabolic heat
& as net export
from ecosystem
energy
in organic wastes, remains
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

15. 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

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)
decomposers, detritivores
(bacteria, crayfish)
1.1
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
top carnivores 21
decomposers + detritivores = 5,080
carnivores
383
herbivores
3,368
producers
20,810 kilocalories/square meter/year
Figure 48.11
Page 874

19. Energy Flow In Silver Springs
Incoming solar
energy not harnessed: 1,679,190 (98.8%)
ENERGY INPUT:
1,700,000 kilocalories
20,810 (1.2%)
Producers
To next trophic level:
Energy in organic wastes and remains:
Energy losses as metabolic heat & as net export from
ecosystem:
Herbivores
Carnivores
Top carnivores
Decomposers,
detritivores
4,245
720 5 90
3,368
383 21
13,197
2,265
272 16
5,060
ENERGY OUTPUT:
Total annual energy flow:
1,700,000 (100%)
Energy Flow In Silver Springs
20, ,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 Atmospheric cycles
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 ocean
425,000
precipitation into ocean 385,000
evaporation from land plants (evapotranspiration) 71,000
surface and groundwater flow 40,000
Ocean
Land
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. bicarbonate and carbonate in ocean water
diffusion between atmosphere and ocean
combustion of fossil fuels
bicarbonate and carbonate in ocean water
photosynthesis
aerobic respiration
marine food webs
death, sedimentation
incorporation into sediments
uplifting
sedimentation
marine sediments
Carbon Cycle - Marine
Figure 48.16 
Page 878

28. combustion of fossil fuels
atmosphere
volcanic action
combustion of fossil fuels
photosynthesis
aerobic respiration
combustion of wood
terrestrial rocks
sedimentation
weathering
land food
webs
soil water
peat,
fossil
fuels
death, burial, compaction over geologic time
leaching, runoff
Carbon Cycle - Land
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 Earth’s surface
Figure 48.18, Page 880

32. Long-term increase in the temperature of Earth’s lower atmosphere
Global Warming
Long-term increase in the temperature of Earth’s 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. excretion, death, decomposition nitrogenous wastes, remains
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
nitrogenous wastes, remains
NO3-
in soil
nitrogen
fixation
dentrification
NH3-,NH4+
in soil
ammonification
2. Nitrification
NO2-
in soil
leaching
1. Nitrification
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 Earth’s crust; no gaseous phase

42. DISSOLVED IN OCEAN WATER DISSOLVED IN SOILWATER, LAKES, RIVERS
Phosphorus Cycle
GUANO
FERTILIZER
TERRESTRIAL ROCKS
LAND FOOD WEBS
DISSOLVED IN OCEAN WATER
MARINE FOOD WEBS
MARINE SEDIMENTS
excretion
weathering
mining
agriculture
uptake
by autotrophs
death, decomposition
sedimentation
settling out
leaching, runoff
uplifting
over geologic time
DISSOLVED IN SOILWATER, LAKES, RIVERS
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