Food webs
Trophic level
Carnivores
3
Herbivores
2
Autotrophs (plants)
1
Trophic level
Omnivore
?
Herbivores
2
Autotrophs (plants)
1
Trophic level
Omnivore
C
?
Herbivores
B
2
Autotrophs (plants)
A
1
Trophic level
4
3
2
1
A
C
B
A
2 Species
2 direct pathways
A→B
B→A
0 indirect pathways
A
B
3 Species
6 direct pathways
A→B
B→A
A→C
C→A
B→C
C→B
6 indirect pathways
A→B →C
A→C →B
B→A →C
B→C →A
C→A →B
C→B →A
Herbivore
(any consumer)
Plant
(any prey)
Bottom-up
Top-down
Predator
Herbivore
Autotroph
Bottom up
Top down
Food Chain Theory
Exploitation Ecosystems
Hypothesis
Oksanen et al, 1981
Equilibrial biomass
Plants
Herbivores
1oCarnivores
2oCarnivores
1TL
2TL
3TL
Potential Primary Productivity
4TL
Green World Hypothesis
Or
“HSS”
Nelson Hairston Sr.
Fred Smith
Larry Slobodkin
Primary predators--3
Herbivores--2
Autotrophs--1
The world is green
Robert T Paine
Apex predators--4
Primary predators--3
Herbivores--2
Autotrophs--1
Lakes and Rivers
Steve
Carpenter
Jim
Kitchell
Predatory Fishes in Lakes
Apex predators
Planktivorous fishes
Zooplankton
Phytoplankton
Courtesy Steve Carpenter
P
M
ZP
Pp
The players
Sea otters
Sea urchins
Macroalgae
Great sharks in
eastern US estuaries
Perturbation--overfishing
Myers et al., Science, 2007
R
B
Bivalves
Elasmobranch
Mesopredators
S
R
B
S
Great Sharks
Grey wolves and boreal forests in
western United States
Bill Ripple
Courtesy Bill Ripple
Courtesy Bill Ripple
Isle of Rùm
New World Tropics
Perturbation—habitat fragmentation
Courtesy John Terborgh
John Terborgh
Jaguar
Harpy eagle
Puma
Population increases on small
islands
• Howler monkey
8.5 to 300X
• Leaf cutter ant colonies
90X
• Rodents
34 to 310X
The Result
Tony Sinclair
The Great Rinderpest
• Ethiopia to tropical east Africa by 1896
• 95% reduction of large grazing animals
• Innoculation/control program in 1950s &
1960s
• THIS IS THE PERTURBATION THAT
UNDERLIES OUR UNDERSTANDING OF
THIS SYSTEM
Prevalence of Rinderpest in Serengeti
% with rinderpest antibodies
100
90
Buffalo
Wildebeest
80
70
60
50
40
30
20
10
0
1950
1955
1960
1965
1970
Serengeti Wildebeest Population
Population Size (x 1000)
1800
1500
1200
900
600
Rinderpest
removed
300
0
1930 1940 1950 1960 1970 1980 1990 2000
Data from Mduma & Sinclair
Mara triangle, northern Serengeti
1944
Photo Syd Downey
1983