Ecosystems

1
Ecosystems

• Chapter 30

2
Ecosystem

• An array of organisms and their physical
  environment, interconnected through a one-way
  flow of energy and cycling of raw materials

3
Modes of Nutrition

• Photoautotrophs
• Capture sunlight or chemical energy
• Primary producers
• Heterotrophs
• Extract energy from other organisms or organic
  wastes
• Consumers, decomposers, detritivores

4
Simple Ecosystem Model
Energy input from sun
Producers Autotrophs (plants and other
self-feeding organisms)
Nutrient Cycling
Consumers Heterotrophs (animals, most fungi, many
protists, many bacteria)
Energy output (mainly metabolic heat)
5
Simple Ecosystem Model

• The role of organisms in an ecosystem

6
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)
7
Trophic Levels

• Feeding relationships
• All organisms at a trophic level are the same
  number of steps away from the energy input into
  the system
• Autotrophs are producers
• closest to energy input
• first trophic level

8
Trophic Levels
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
9
Food Chain

• Food chain

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
plants
11
marsh hawk
Connections in a tallgrass prairie food web
Higher Trophic Levels
crow
upland sandpiper
garter snake
frog
weasel
badger
coyote
spider
Second Trophic Level
sparrow
ground squirrel
pocket gopher
prairie vole
earthworms, insects
First Trophic Level
grasses, composites
Fig. 30-4, p.529
12
Energy Losses

• Energy transfers are never 100 efficient
• Some energy is lost at each step
• Limits number of trophic levels in an ecosystem

13
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 and as net
export from ecosystem
energy in organic wastes, remains
energy in organic wastes, remains
energy losses as metabolic heat and as net
export from ecosystem
herbivores
decomposers
decomposers
carnivores
detritivores
detritivores
decomposers
Energy Output
Energy Output
14
Biological Magnification

• Nondegradable or slowly degradable substances
  become more and more concentrated in tissues of
  organisms at higher trophic levels of a food web

15
DDT in Food Webs

• Synthetic pesticide banned in United States since
  1970s
• Carnivorous birds accumulate DDT in their
  tissues, produce brittle egg shells

16
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
17
Ecological Pyramids

• Primary producers are bases for successive tiers
  of consumers
• Biomass pyramid
• Dry weight of all organisms
• Energy pyramid
• Usable energy decreases as it is transferred
  through ecosystem

18
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

19
Net Primary Productivity
20
Biogeochemical Cycle

• Flow of an essential substance from the
  environment to living organisms and back to the
  environment
• Main reservoir is in the environment
• Geologic processes, decomposers aid cycles

21
Three Categories

• Hydrologic cycle
• Water
• Atmospheric cycles
• Nitrogen and carbon
• Sedimentary cycles
• Phosphorus and other nutrients