Ecosystems

1
Ecosystems

• Chapter 28

2
Ecosystems

• Chapter 28

Fig. 41-1, p.730
3
Ecosystem

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

4
Modes of Nutrition

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

5
Simple Ecosystem Model
Autotrophs (plants, other self-feeding organisms)
Heterotrophs (animals, most fungi, many
protists, many bacteria)
(mainly metabolic heat)
6
Consumers

1. Herbivores
2. Carnivores
3. Parasites
4. Omnivores
5. Decomposers
6. Detritivores

7
Omnivores, Red FoxDiet fluctuations due to
Seasonal variation in diet
fruits
rodents, rabbits
insects
SPRING
birds
fruits
rodents, rabbits
insects
SUMMER
birds
fruits
rodents, rabbits
insects
FALL
birds
fruits
insects
rodents, rabbits
birds
WINTER
8
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

9
Trophic Levels in Prairie
Fourth-level consumers (heterotrophs)
Top carnivores, parasites, detritivores,
decomposers
5th
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
10
Food Chain
marsh hawk

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

upland sandpiper
garter snake
cutworm
flowering plant
11
Food Web
12
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

13
Energy Losses

• The mouse receives energy from the food it eats.
• Cells extract the food's energy for growth,
  acquiring food, escaping enemies lost as heat.
• Some of the energy that is in the food is lost in
  the mouse's waste (feces).
• The remaining energy is stored in the mouse's
  body and is available to the organism that preys
  on it.
• About 90 of the energy is used or lost, only 10
  is available to predators.

14
Two Types of Food Webs
Grazing Food Web
Detrital Food Web
Producers (photosynthesizers)
Producers (photosynthesizers)
decomposers
herbivores
carnivores
detritivores
decomposers
ENERGY OUTPUT
ENERGY OUTPUT
15
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
• Dichloro-Diphenyl-Trichloroethane (DDT)
• Polychlorinated biphenyls (PCBs)

16
DDT in Food Webs

• Synthetic pesticide banned in the United States
  since the 1970s
• Birds that were top carnivores accumulated DDT in
  their tissues

17
DDT
18
PCBs in Food Webs

• PCB concentrations in animal tissue can be
  magnified up to 25 million times.
• Microscopic organisms pick up chemicals from
  sediments
• Consumed in large numbers by filter feeding
  zooplankton.
• Mysid shrimp then consume zooplankton
• fish eat the mysid
• and so on up the food web to the herring gull.
• (Figure and caption from Our Stolen Future, p.
  27)

19
DDT Detection

• In 1962, Rachel Carson, a former U.S. Fish and
  Wildlife Service (USFWS) scientist and writer,
  published Silent Spring, outlining the dangers of
  DDT

Fig. 41-8, p.736
20
DDT in Food Webs

• Heinz Meng
• Responsible for the reintroduction of the
  Peregrine Falcon.

21
DDT residues

• Why was there never a concern for the Ring-billed
  gulls?

Fig. 41-7, p.736
22
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

23
Primary Productivity Varies

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

24
Biomass Pyramid (energy)

• 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)
11
first-level consumers (herbivorous
fishes, turtles, invertebrates)
37
5
primary producers (algae, eelgrass, rooted plants)
809
decomposers, detritivores (bacteria, crayfish)
25
Silver Springs Annual Energy Flow
ENERGY INPUT
17,000,000 kilocalories
incoming solar energy not harnessed
energy transfers through ecosystem
1,679,190 (98.8)
20,810 (1.2)
producers
energy losses as metabolic heat and as net export
from the ecosystem
transferred to the next trophic level
energy still in organic wastes and remains
3,368
4,245
13,197
herbivores
383
720
2,265
carnivores
21
272
90
top carnivores
5
16
decomposers, detritivores
5,060
ENERGY OUPUT TOTAL ANNUAL ENERGY FLOW
20,810 1,679,190
1,700,000 (100)
26
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
decomposers detritivores 5,060
21
carnivores
herbivores
383
3,368
producers
20,810
27
Primary Productivity

• Although average productivity per unit surface
  area is lower than on land, Total productivity on
  land and in seas is about equal..Due to amount of
  water coverage. (Red high ?Purple lowest)

28
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

29
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

30
Nutrient Flow Land Ecosystem
31
Three Categories

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

32
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
Oceans
Land
33
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

34
Hubbard Brook Experiment
losses from disturbed watershed plot
time of deforestation
35
Aquifer Depletion

• Green signifies high overdrafts
• Gold, moderate overdrafts
• Yellow, insignificant withdrawals
• Shaded areas show groundwater pollution
• Blue squares saltwater intrusion

36
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

37
Carbon Cycle
diffusion
Atmosphere
Bicarbonate, carbonate
Terrestrial rocks
Land food webs
Marine food webs
Soil water
Peat, fossil fuels
Marine Sediments
38
Carbon in the Oceans

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

39
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

40
Greenhouse Effect

• Greenhouse gases impede the escape of heat from
  Earths surface

41
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

42
Carbon Dioxide Increase
43
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

44
Greenhouse Gases
carbon dioxide
methane
nitrous oxide
CFCs
45
Global Warming

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

46
Nitrogen Cycle

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

47
Nitrogen Cycle
48
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

49
Ammonification Nitrification

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

50
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

51
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

52
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

53
Phosphorus Cycle
mining
FERTILIZER
excretion
GUANO
agriculture
weathering
uptake by autotrophs
uptake by autotrophs
weathering
LAND FOOD WEBS
DISSOLVED IN OCEAN WATER
MARINE FOOD WEBS
DISSOLVED IN SOILWATER, LAKES, RIVERS
death, decomposition
death, decomposition
leaching, runoff
sedimentation
setting out
uplifting over geologic time
ROCKS
MARINE SEDIMENTS
54
Phosphorus Cycle

• If too much fertilizer is added to the soil what
  is not absorbed by plants leaches into to local
  water ways.
• This leads to the eutrification of rivers, ponds
  and lakes.
• The process in which oxygen is removed from the
  water by the decomposition of large amounts of
  organic matter

55
Human Effects

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