Download Energy Flow

Energy Flow & Nutrient Cycle
Big bugs have little bugs upon their
backs to bite ‘em
Little bugs have lesser ones an so ad
infinitum.
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
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
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
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
Energy Flow
Energy Flow through an Ecosystem
Food Chain
Producer
grass
Primary
Consumer
grasshopper
Tertiary
Consumer
Secondary
Consumer
snake
hawk
heat
heat
heat
Nutrients
fungi
Decomposer
Transfer Efficiencies
• Efficiency of energy transfer called
transfer efficiency
• Units are energy or biomass
Et = Pt
Pt-1
Pt = annual production at
level t
Pt-1 = annual production
at t-1
Transfer Efficiency Example
• Net primary production = 150 g C/m2/yr
• Herbivorous copepod production = 25 g C/m2/yr
Et = Pt = Pcopepods
= 25 = 0.17
Pt-1 P
150
phytoplankton
• Typical transfer efficiency ranges
*Level 1-2 ~20%
*Levels 2-3, …: ~10%
Cellular
Respiration
Feces
Growth
Food Webs
• Food chains don’t exist in real
ecosystems
• Almost all organisms are eaten by
more than one predator
• Food webs reflect these multiple
and shifting interactions
Antarctic Food Web
Some Feeding Types
Many species don’t fit into convenient categories
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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
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)
Fish (0.2 units)
Carnivorous
Zooplankton A
(1 units)
Carnivorous
Zooplankton B
(1 units)
Fish (0.1 units)
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
Microbial Loop
Solar
Energy
Phytoplankton
Herbivores
CO2
nutrients
Planktivores
DOC
Piscivores
Bacteria
Nanoplankton
(protozoans)
An Ecological Mystery
Keystone Species
Kelp Forests
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%
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?
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