Ecosystems

1
Ecosystems

• Chapter 30

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 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 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
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
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