Energy Flow

1
Energy Flow Nutrient Cycle
Big bugs have little bugs upon their backs to
bite em Little bugs have lesser ones an so ad
infinitum.
2

• Food Chains
• Artificial devices to illustrate energy flow from
  one trophic level to another
• Trophic Levels groups of organisms that obtain
  their energy in a similar manner

3
(No Transcript)
4
Food Chains

• Total number of levels in a food chain depends
  upon locality and number of species
• Highest trophic levels occupied by adult animals
  with no predators of their own
• Secondary Production total amount of biomass
  produced in all higher trophic levels

5
Nutrients

• Inorganic nutrients incorporated into cells
  during photosynthesis
• - e.g. N, P, C, S
• Cyclic flow in food chains
• Decomposers release inorganic forms that become
  available to autotrophs again

6
Energy

• Non-cyclic, unidirectional flow
• Losses at each transfer from one trophic level to
  another
• - Losses as heat from respiration
• - Inefficiencies in processing
• Total energy declines from one transfer to
  another
• - Limits number of trophic levels

7
Energy Flow
8
Energy Flow through an Ecosystem
Food Chain
Tertiary Consumer
Producer
Primary Consumer
Secondary Consumer
grasshopper
snake
grass
hawk
heat
heat
heat
Nutrients
fungi
Decomposer
9
Transfer Efficiencies

• Efficiency of energy transfer called transfer
  efficiency
• Units are energy or biomass

Pt annual production at level t Pt-1 annual
production at t-1
Et Pt Pt-1
10
Transfer Efficiency Example

• Net primary production 150 g C/m2/yr
• Herbivorous copepod production 25 g C/m2/yr

Pcopepods
Et Pt Pt-1
25 0.17
Pphytoplankton
150

• Typical transfer efficiency ranges
• Level 1-2 20
• Levels 2-3, 10

11
Energy Biomass Pyramids
12
Energy Use By An Herbivore
13
Food Webs

• Food chains dont exist in real ecosystems
• Almost all organisms are eaten by more than one
  predator
• Food webs reflect these multiple and shifting
  interactions

14
Antarctic Food Web
15
Some Feeding Types
Many species dont fit into convenient categories

• Algal Grazers and Browsers
• Suspension Feeding
• Filter Feeding
• Deposit Feeding
• Benthic Animal Predators
• Plankton Pickers
• Corallivores
• Piscivores
• Omnivores
• Detritivores
• Scavengers
• Parasites
• Cannibals
• Ontogenetic dietary shifts

16
Food Webs
Competitive relationships in food webs can reduce
productivity at top levels
Phytoplankton (100 units)
Phytoplankton (100 units)
Herbivorous Zooplankton (20 units)
Herbivorous Zooplankton (20 units)
Carnivorous Zooplankton A (2 units)
Carnivorous Zooplankton A (1 units)
Carnivorous Zooplankton B (1 units)
Fish (0.2 units)
Fish (0.1 units)
17
Recycling The Microbial Loop

• All organisms leak and excrete dissolved organic
  carbon (DOC)
• Bacteria can utilize DOC
• Bacteria abundant in the euphotic zone (5
  million/ml)
• Numbers controlled by grazing due to nanoplankton
• Increases food web efficiency

18
Microbial Loop
Solar Energy
Phytoplankton
Herbivores
CO2 nutrients
Planktivores
DOC
Piscivores
Bacteria
Nanoplankton (protozoans)
19
An Ecological Mystery
20
Keystone Species
Kelp Forests
21
An Ecological Mystery

• Long-term study of sea otter populations along
  the Aleutians and Western Alaska
• 1970s sea otter populations healthy and
  expanding
• 1990s some populations of sea otters were
  declining
• Possibly due to migration rather than mortality
• 1993 800km area in Aleutians surveyed
• - Sea otter population reduced by 50

22

• Vanishing Sea Otters
• 1997 surveys repeated
• Sea otter populations had declines by 90
• - 1970 53,000 sea otters in survey area
• - 1997 6,000 sea otters
• Why?
• - Reproductive failure?
• - Starvation, pollution disease?

23

• Cause of the Decline
• 1991 one researcher observed an orca eating a
  sea otter
• Sea lions and seals are normal prey for orcas
• Clam Lagoon inaccessible to orcas- no decline
• Decline in usual prey led to a switch to sea
  otters
• As few as 4 orcas feeding on otters could account
  on the impact
• - Single orca could consume 1,825 otters/year

24
(No Transcript)
25
(No Transcript)