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Chapter 10 Predation. © 2002 by Prentice Hall, Inc. Upper Saddle River, NJ 07458. Outline. There are a variety of antipredator adaptations, which suggests that predation is important in nature Predator-prey models can explain many outcomes

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chapter 10 predation

Chapter 10Predation

© 2002 by Prentice Hall, Inc.

Upper Saddle River, NJ 07458

outline
Outline
  • There are a variety of antipredator adaptations, which suggests that predation is important in nature
  • Predator-prey models can explain many outcomes
  • Field data suggests that predators have a large impact on prey populations
outline3
Outline
  • Experiments involving the removal or introduction of exotic predators provide good data on the effects of predators on their prey
  • Field experiments involving the manipulations of native populations show predation to be a strong force
equilibrium theories of population regulation
Equilibrium theories of population regulation
  • A.   Extrinsic biotic school
    • 1.   Food supply and population regulation
    • 2.   Predation and population regulation
    • 3.   Disease and population
  • B.   Intrinsic school
    • 1.   Stress and territoriality
    • 2.   Genetic polymorphism hypothesis
    • 3.   Dispersal
the causes of population change
The causes of population change

key factor analysis 主導因子分析

(一) Density-dependent factor 密度制約因子:

(種內、種間因素)作用強度隨種群密度而變。A factor affecting population size whose intensity of action varies with density.

(二) )Density independent factor非密度制約因素 (外界環境因素):

having an influence on individuals that does not vary with the number of individuals per unit area in the population.

density dependent factor 1
Density-dependent factor 密度制約因子:1. 種間因素

.食物、空間資源  種內、種間競爭

.病蟲害傳播速度

.個體成熟速度

.體質和繁殖力、生長發育、自相殘殺、外遷

.植物結實數量

.抗逆性

在橡樹蛾的生活史裡,有不同的生活環境,不同的掠食者,寄生、競爭、環境壓力,在不同時期裡會有不同的死亡率。

slide7
2.種間因素

.競爭

.掠食、寄生

.遺傳反饋機制(抗病種的培育)

澳洲野兔  粘液病毒  抗病種

density independent factor
Density independent factor

.氣候因素

.土壤因素

.營養

.理化

.空間

.汙染

extrinsic factors
Extrinsic factors:

External factors acting on populations

. Predation, parasitism

. Competition for food  density depended

. Competition for space  density depended

. Random stochastic change  density independent

. Weather

slide10
1.種內因素

種群是一個具有自我調節 (self regulation)機制的生活系統,可以按照自身的性質及環境狀況調節它們的數量。

*植物的自疏現象

*禾本科植物的分的產生和生長

*遺傳特性(抗逆性)

*內分泌調節(旅鼠)

Crowding stress 腎上腺髓質(adrenocorticotropin)

腦下腺 (Epinephrine) 腎上腺皮質(Corticoids)

危急反應 Alarm response

introduction
Introduction
  • Wolves in Yellowstone Park (Figure 10.1)
    • U.S. Fish and Wildlife Service, 1980’s
    • Reintroduce in Yellowstone Park and stabilize wolf populations in Minnesota and Montana
    • Concerns
      • Cattle ranchers concerned: Decimate herd?
      • Are predators tied to the health of the main prey?
      • Can predators switch prey?
      • Ramifications to reestablishment
    • Results: No major effects
introduction12
Introduction
  • Predation
    • Traditional view: carnivory
    • Differences from herbivory
      • Herbivory is non-lethal
    • Differences from parasitism
      • In parasitism, one individual is utilized for the development of more than one parasite
introduction13

High

Intimacy

Parasitoids

Parasite

Low

Predator

Grazer

High

Lethality

Low

Introduction
  • Predation (cont.)
    • Predator-prey associations
      • Figure 10.2
antipredator adaptations
Antipredator Adaptations
  • Aposematic or warning coloration
    • Advertises an unpalatable taste
    • Ex. Blue jays and monarch butterflies
      • Caterpillar obtains poison from milkweed
antipredator adaptations15
Antipredator Adaptations
  • Ex. Blue jays and monarch butterflies (cont.)
    • Blue jays suffer violent vomiting from ingesting caterpillar
  • Ex. Tropical frogs
    • Toxic skin poisons
    • Figure 10.3a
antipredator adaptations16
Antipredator Adaptations
  • Camouflage
    • Blending of organism into background color
    • Grasshoppers (Figure 10.3b)
antipredator adaptations17
Antipredator Adaptations
  • Camouflage (cont.)
    • Stick insects mimic twigs and branches
    • Zebra stripes: blend into grassy background
  • Mimicry
antipredator adaptations18
Antipredator Adaptations
  • Mimicry (cont.)
    • Animals that mimic other animals
      • Ex. Some hoverflies mimic wasps Mimicry
    • Types of mimicry
      • Müllerian mimicry
        • Fritz Müller, 1879
        • Unpalatable species converge to look the same
antipredator adaptations19
Antipredator Adaptations
    • Unpalatable species converge to look the same (cont.)
      • Reinforce basic distasteful design
      • Ex. Wasps and some butterflies
      • Mimicry ring: a group of sympatric species, often different taxa, share a common warning pattern
  • Batesian mimicry
    • Henry Bates, 1862
    • Mimicry of unpalatable species by palatable species
antipredator adaptations20
Antipredator Adaptations
  • Batesian mimicry (cont.)
    • Ex. hoverflies resemble stinging bees and wasps (Figure 10.3d)
antipredator adaptations21
Antipredator Adaptations
  • Difficulty distinguishing type of mimicry
    • Monarch butterflies and viceroy butterflies (Figures 10.3d,e)
antipredator adaptations22
Antipredator Adaptations
  • Displays of intimidation
    • Ex. Toads swallow air to make themselves appear larger
    • Ex. Frilled lizards extend their collars to produce the same effect (Figure 10.3f)
antipredator adaptations23
Antipredator Adaptations
  • Polymorphism
    • Two or more discrete forms in the same population
    • Color polymorphism
      • Predator has a preference (usually the more abundant form)
      • Prey can proliferate in the rarer form
antipredator adaptations24
Antipredator Adaptations
  • Color polymorphism (cont.)
    • Ex. leafhopper nymphs (orange and black)
    • Ex. Pea aphids (red and green)
  • Reflexive selection
    • Every individual is slightly different
    • Examples: brittle stars, butterflies, moths, echinoderms, and gastropods
antipredator adaptations25
Antipredator Adaptations
    • Reflexive selection (cont.)
      • Thwart predators’ learning processes
  • Prey phenologically separated from predator
    • Ex. Fruit bats
      • Either diurnal or nocturnal
      • Only nocturnal in the presence of predatory diurnal eagles
antipredator adaptations26
Antipredator Adaptations
  • Chemical defense
    • Used to ward off predators
    • Ex. bombardier beetles
      • Possess a reservoir of hydroquinone and hydrogen perioxide
      • When threatened, eject chemicals into “explosion chamber”
antipredator adaptations27
Antipredator Adaptations
    • Ex. bombardier beetles (cont.)
      • Mix with peroxidase enzyme
      • Mixture is violently sprayed at attacker
  • Masting
    • Synchronous production of many progeny by all individuals in population
antipredator adaptations28
Antipredator Adaptations
  • Masting (cont.)
    • Satiate predators
    • Allows for some progeny to survive
    • Common to seed herbivory
    • Ex. 17-year and 13-year periodical cicadas
antipredator adaptations29
Antipredator Adaptations
  • Comparison of defense mechanisms
    • Table 10.1, chemical defense is most common
predator prey models
Predator-Prey Models
  • Effects of predators on prey
  • Depend on such things as prey and predator densities, and predator efficiency
  • Graphical method to monitor relationship
predator prey models32
Predator-Prey Models
  • Graphical method to monitor relationship (cont.)
    • Prey isoclines have characteristic hump shape
      • Figure 10.4
slide33

i) Prey iscoline

N

2

Predator density

Prey increase

N

K

ii) Predator iscoline

1

1

N

2

K

2

Predator increases

Predator decreases

Predator density

N

Prey density

1

predator prey models34
Predator-Prey Models
  • Prey isoclines have characteristic hump shape (cont.)
    • In the absence of predators, prey density would be equal to the carrying capacity, K1
    • Lower limit, individuals become too rare to meet for reproduction
predator prey models35
Predator-Prey Models
  • Prey isoclines have characteristic hump shape (cont.)
    • Between these two values, prey population can either increase or decrease depending on predator density
    • Above the isocline, prey populations decline
predator prey models36
Predator-Prey Models
  • Prey isoclines have characteristic hump shape (cont.)
    • Below the isocline, prey populations increase
  • Predator isoclines
    • Threshold density, where predator population will increase
    • Predator population can increase to carrying capacity
predator prey models37
Predator-Prey Models
  • Predator isoclines (cont.)
    • Mutual interference or competition between predators
      • More prey required for a given density predator
      • Predator isoclines slopes toward the right
  • Superimpose prey and predator isoclines
    • Figure 10.5
predator prey models38
Predator-Prey Models
  • Superimpose prey and predator isoclines (cont.)
    • One stable point emerges: the intersection of the lines
    • Three general cases
      • Inefficient predators require high densities of prey (Figure 10.5a)
slide39

a)

Damped oscillations

Predator

isocline

Prey

isocline

predator prey models40
Predator-Prey Models
  • Three general cases (cont.)
    • A moderately efficient predator leads to stable oscillations of predator and prey populations (Figure 10.5b)
slide41

Stable oscillations

b)

Predator

equilibrium

density

Population density

predator prey models42
Predator-Prey Models
  • Three general cases (cont.)
    • A highly efficient predator can exploit a prey nearly down to its limiting rareness (Figure 10.5c)
slide43

c)

Increasing oscillations

Predator density

predator prey models44
Predator-Prey Models
  • All based on how efficient predator is
  • Shift in isoclines
    • Prey starvation (shift to left)
    • Food enrichment (shift to right) (Figure 10.5d)
slide45

“The paradox of enrichment”

d)

K1

increases to K1* with enrichment

Prey

Prey isocline

changes

Predator isocline

remains unchanged

Predator

K1

K1*

predator prey models46
Predator-Prey Models
  • Food enrichment (shift to right) (cont.)
    • Carrying capacity changes
    • Predator isocline changes – “paradox enrichment” : Increases in nutrients or food destabilizes the system
predator prey models47
Predator-Prey Models
  • Functional response
    • How an individual predator responds to prey density can affect how predators interact with prey (Figure 10.6)
slide48

I

Number of prey eaten per predator

II

III

Prey density

predator prey models49
Predator-Prey Models
  • Functional response (cont.)
    • Three types
      • Type I: Individuals consume more prey as prey density increases
      • Type II: Predators can become satiated and stop feeding, or limited by handling time.
predator prey models50
Predator-Prey Models
  • Three types (cont.)
    • Type III: Feeding rate is similar to logistic curve; low at low prey densities, but increases quickly at high densities
  • Changes in prey consumption
    • Functional response changes (Figure 10.7)
predator prey models51
Predator-Prey Models
  • Functional response changes (cont.)
    • Dictates how individual predators respond to prey population
  • Numerical response changes
    • Governs how a predator population migrates into and out of areas in response to prey densities
field studies of predator prey interactions
Field Studies of Predator-Prey Interactions
  • Field comparisons to models
  • Do predators control prey populations?
  • Importance of predators in controlling prey density
    • Kaibab deer herd
      • Kaibab Plateau (Northern Arizona)
field studies of predator prey interactions53
Field Studies of Predator-Prey Interactions
  • Kaibab deer herd (cont.)
    • Declared a national park around 1900
    • All big predators were removed and deer hunting was prohibited
    • Estimates of 10 fold increase in deer population
    • Reevaluated by Graham Caughley (1970)
field studies of predator prey interactions54
Field Studies of Predator-Prey Interactions
    • Reevaluated by Graham Caughley (1970) (cont.)
      • Predator control had some impact; cessation of hunting and removal of competing sheep and cattle also had an impact
  • Serengeti plains of eastern Africa
    • Large predators have little effect on large mammal prey
field studies of predator prey interactions55
Field Studies of Predator-Prey Interactions
  • Serengeti plains of eastern Africa (cont.)
    • Most prey taken are either injured or senile
    • Contribute little to future generations
    • Prey are migratory
  • Moose population on Michigan's Isle Royale
field studies of predator prey interactions56
Field Studies of Predator-Prey Interactions
  • Moose population on Michigan's Isle Royale (cont.)
    • Wolf-free existence until 1949.
    • Durwood Allen (1958) began to track wolf and moose populations
    • Trends in populations (Figure 10.8)
slide57

2600

2400

2200

60

2000

Moose

1800

50

1600

1400

40

1200

Moose

Wolves

30

1000

800

20

600

400

10

Wolves

200

0

0

1990

1997

1955

1960

1965

1970

1975

1980

1985

1995

Year

field studies of predator prey interactions58
Field Studies of Predator-Prey Interactions
  • Trends in populations (cont.)
    • Wolf population
      • Peaked at 50 in 1980
      • Severe nosedive in 1981
      • Small recovery in the late 1990s
    • Moose population
      • Increased steadily in the 1960s and 1970s
      • Declined as the wolf population increased until 1981
field studies of predator prey interactions59
Field Studies of Predator-Prey Interactions
  • Moose population (cont.)
    • A record population of 2500 was reached in 1995, when the wolf population was low
    • Good evidence of prey population control by predators
    • Confounded in 1996 when the moose population crashed - starvation
field studies of predator prey interactions60
Field Studies of Predator-Prey Interactions
  • Canada lynx and snowshoe hare
    • Populations show dramatic cyclic oscillations every 9 to 11 years (Figure 10.9)
slide61

Abundance

of lynx

Abundance

of hares

120

200

180

100

160

140

80

120

Abundance of hares (x 1000)

Abundance of lynx (x 1000)

60

100

80

40

60

40

20

20

1850

1860

1870

1880

1890

1900

1910

1920

1930

1940

field studies of predator prey interactions62
Field Studies of Predator-Prey Interactions
  • Canada lynx and snowshoe hare (cont.)
    • Cycle has existed as long as records have existed (over 200 years)
    • An example of intrinsically stable predator-prey relationship
introduced predators
Introduced Predators
  • Method for determining the effects of predators
  • Dingo predations on kangaroos in Australia
    • Dingo
      • Introduced species
      • Largest Australian carnivore
introduced predators64
Introduced Predators
  • Dingo (cont.)
    • Predator of imported sheep
    • Eliminated from certain areas
      • Spectacular increases in native species
        • 160 fold increase in red kangaroos
        • Over 20 fold increase in emus
introduced predators65
Introduced Predators
  • Dingo (cont.)
    • Effects on feral pigs
      • Shortage of young pigs
      • Considerable impact on recruitment of pigs (Figure 10.10)
slide66

6+

5-6

4-5

3-4

Age class (years)

2-3

1-2

0.5-1

>.05

60

20

40

60

40

20

0

Females (%)

Males (%)

(a) Dingoes present

6+

5-6

4-5

3-4

Age class (years)

2-3

1-2

0.5-1

>.05

60

20

40

60

40

20

0

Males (%)

Females (%)

(a) Dingoes present

introduced predators67
Introduced Predators
  • European foxes and feral cats in Australia
    • Damage domestic livestock
    • Effects when removed (Figure 10.11)
slide68

60

40

Predators shot

No shooting

Mean no. of rabbits per km of transect

20

0

1981

1982

introduced predators69
Introduced Predators
  • Lamprey and the Great Lakes
    • Construction of Wetland Canal allowed lamprey to enter the Great Lakes
    • Dramatic reduction in lake trout (Figure 10.12)
slide70

7

Lake Huron

6

Mean production

5

4

3

2

1

0

Lake Michigan

7

Mean production

6

5

Lake trout production (millions per pound)

4

3

2

1

0

7

Lake Superior

6

5

Mean production

4

3

2

1

0

1930

1935

1940

1945

1950

1955

1960

introduced predators71
Introduced Predators
  • Lamprey and the Great Lakes (cont.)
    • Trout recovered after lamprey population was reduced
field experiments with natural systems
Field Experiments with Natural Systems
  • Lions in South Africa
    • Kruger National Park, 1903
    • Lions Shot
    • Number of large prey increased
    • Shooting of lions ends, 1960
    • Wildebeast increase so much that their numbers had to be culled from 1965 to 1972
field experiments with natural systems73
Field Experiments with Natural Systems
  • Gray partridge, European game bird
    • Figure 10.13
field experiments with natural systems74
Field Experiments with Natural Systems
  • Gray partridge, European game bird (cont.)
    • Over 20 million shot in Great Britain in the 1930s
    • Only 3.8 million shot in the mid-1980s
      • High chick mortality due to starvation
field experiments with natural systems75
Field Experiments with Natural Systems
  • Only 3.8 million shot in the mid-1980s (cont.)
    • Reduced insects due to introduction of herbicides in the 1950s was suspected
    • However, smaller populations in areas where there was no control of predators by gamekeepers
field experiments with natural systems76
Field Experiments with Natural Systems
  • Only 3.8 million shot in the mid-1980s (cont.)
    • Predation control increased
      • The number of partridges that bred successfully
      • The average size of the broods
      • Partridge populations by 75 %
field experiments with natural systems77
Field Experiments with Natural Systems
  • Predators and rodents in Finland
    • Large scale removal of predators, April 1992 and 1995 over 2-3 km2
    • Large increase in rodent population by June (compared to control plots) (Figure 10.14)
slide78

3.5

3

2.5

Mean number of

rodents per sample

2

1.5

1

Without predators

0.5

0

June

April

3.5

3

2.5

Mean number of

rodents per sample

2

1.5

1

0.5

With predators

0

June

April

applied ecology
Applied Ecology
  • Humans as predators - whaling
    • Exploitation necessary
    • Is harvesting at any level sustainable?
  • History of Antarctic whaling
    • Figure 1
applied ecology80
Applied Ecology
  • History of Antarctic whaling (cont.)
    • 1930s, blue whales primarily harvested
    • 1950s, blue whale population depleted, replaced with fin whale
    • 1960s, fin whale population collapsed
applied ecology81
Applied Ecology
  • History of Antarctic whaling (cont.)
    • 1960s, humpback whale population collapsed
    • Prior to 1958, Sei whales hardly ever harvested
      • Reduction in other whales made Sei whale attractive
applied ecology82
Applied Ecology
  • Prior to 1958, Sei whales hardly ever harvested (cont.)
    • Peak harvest of about 20,000 by 1964-65
    • Catches declined thereafter due to limitations
  • The relatively small minke whale
    • Was ignored in the southern oceans until 1971-72
applied ecology83
Applied Ecology
  • The relatively small minke whale (cont.)
    • Began to be taken, and is now the largest component of the southern baleen whale catch
  • Whale ban proposed in 1985-86, took effect in 1988
applied ecology84
Applied Ecology
    • Iceland, Norway, and Japan, 1994
      • Argued for resumption of limited commercial whaling
  • Should we ban commercial whaling?
  • Whale populations are recovering
applied ecology85
Applied Ecology
  • Whale populations are recovering (cont.)
    • Ex. Blue whale populations have increased four fold
    • Ex. California grey whales have recovered to prewhaling levels
summary
Summary
  • Predation is a strong selective force in nature
    • Aposematic coloration
    • Camouflage
    • Batesian and Mullerian mimicry
    • Intimidation displays
    • Polymorphisms
summary87
Summary
  • Predation is a strong selective force in nature (cont.)
    • Chemical defenses
  • Modeling predator-prey interactions
    • Even simple predator-prey models show
summary88
Summary
  • Even simple predator-prey models show (cont.)
    • Stable cycles
    • Wildly increasing and unstable oscillations
  • Difficulty in predicting or modeling how predators and prey interact
    • Mutual interference between predators
summary89
Summary
  • Difficulty in predicting or modeling how predators and prey interact (cont.)
    • Existence of specific predator territory sizes
    • Ability of predators to feed on more than one type of prey
summary90
Summary
  • Large-scale observations support
    • Predators only take weak and sickly individuals
    • Prey populations influence predator numbers, not vice versa
summary91
Summary
  • Accidental or deliberate introductions of exotic predators
    • Profound effects on native prey populations
    • Predators have important regulatory effects on prey
summary92
Summary
  • Accidental or deliberate introductions of exotic predators (cont.)
    • May not be indicative of “natural systems”
summary93
Summary
  • Evidence from natural systems
    • Most studies have concluded that predators have a significant effect on prey
discussion question 1
Discussion Question #1
  • Should ranchers be concerned about the reintroduction into their vicinity of large predators, like wolves and panthers?
discussion question 2
Discussion Question #2
  • Do sea lions, otters, or dolphins decrease the stock of fish available for people that fish?
discussion question 3
Discussion Question #3
  • Would the number of deer available for hunters be the same in the presence of large predators?
discussion question 4
Discussion Question #4
  • What data would you need to collect to answer the above 3 questions?
discussion question 5
Discussion Question #5
  • What can the effects of exotic predators tell us about the strength of predation? What can't they tell us?
discussion question 6
Discussion Question #6
  • Which do you think more likely: that predators control prey populations or that prey control predator populations? Would the answer vary according to the particular system? Give an example.
discussion question 7
Discussion Question #7
  • What shortcomings do you think Rosenzweig and MacArthur's predator and prey isoclines have? What would these shortcomings mean in terms of determining how predators and prey interact?
discussion question 8
Discussion Question #8
  • A great many fish stocks seem to have been overfished. How do you think we could prevent overfishing? What biological information do we need to have, and how can we get it when we can't see the population in question?
predator prey models102
Predator-Prey Models
  • Prey isoclines have characteristic hump shape (cont.)
    • Below the isocline, prey populations increase
  • Predator isoclines
    • Threshold density, where predator population will increase
    • Predator population can increase to carrying capacity
predator prey models103
Predator-Prey Models
  • Predator isoclines (cont.)
    • Mutual interference or competition between predators
      • More prey required for a given density predator
      • Predator isoclines slopes toward the right
  • Superimpose prey and predator isoclines
    • Figure 10.5
predator prey models104
Predator-Prey Models
  • Superimpose prey and predator isoclines (cont.)
    • One stable point emerges: the intersection of the lines
    • Three general cases
      • Inefficient predators require high densities of prey (Figure 10.5a)
slide105

a)

Damped oscillations

Predator

isocline

Prey

isocline

predator prey models106
Predator-Prey Models
  • Three general cases (cont.)
    • A moderately efficient predator leads to stable oscillations of predator and prey populations (Figure 10.5b)
slide107

Stable oscillations

b)

Predator

equilibrium

density

Population density

predator prey models108
Predator-Prey Models
  • Three general cases (cont.)
    • A highly efficient predator can exploit a prey nearly down to its limiting rareness (Figure 10.5c)
slide109

c)

Increasing oscillations

Predator density

predator prey models110
Predator-Prey Models
  • All based on how efficient predator is
  • Shift in isoclines
    • Prey starvation (shift to left)
    • Food enrichment (shift to right) (Figure 10.5d)
slide111

“The paradox of enrichment”

d)

K1

increases to K1* with enrichment

Prey

Prey isocline

changes

Predator isocline

remains unchanged

Predator

K1

K1*

predator prey models112
Predator-Prey Models
  • Food enrichment (shift to right) (cont.)
    • Carrying capacity changes
    • Predator isocline changes – “paradox enrichment” : Increases in nutrients or food destabilizes the system
predator prey models113
Predator-Prey Models
  • Functional response
    • How an individual predator responds to prey density can affect how predators interact with prey (Figure 10.6)
slide114

I

Number of prey eaten per predator

II

III

Prey density

predator prey models115
Predator-Prey Models
  • Functional response (cont.)
    • Three types
      • Type I: Individuals consume more prey as prey density increases
      • Type II: Predators can become satiated and stop feeding, or limited by handling time.
predator prey models116
Predator-Prey Models
  • Three types (cont.)
    • Type III: Feeding rate is similar to logistic curve; low at low prey densities, but increases quickly at high densities
  • Changes in prey consumption
    • Functional response changes (Figure 10.7)
predator prey models117
Predator-Prey Models
  • Functional response changes (cont.)
    • Dictates how individual predators respond to prey population
  • Numerical response changes
    • Governs how a predator population migrates into and out of areas in response to prey densities
field studies of predator prey interactions118
Field Studies of Predator-Prey Interactions
  • Field comparisons to models
  • Do predators control prey populations?
  • Importance of predators in controlling prey density
    • Kaibab deer herd
      • Kaibab Plateau (Northern Arizona)
field studies of predator prey interactions119
Field Studies of Predator-Prey Interactions
  • Kaibab deer herd (cont.)
    • Declared a national park around 1900
    • All big predators were removed and deer hunting was prohibited
    • Estimates of 10 fold increase in deer population
    • Reevaluated by Graham Caughley (1970)
field studies of predator prey interactions120
Field Studies of Predator-Prey Interactions
    • Reevaluated by Graham Caughley (1970) (cont.)
      • Predator control had some impact; cessation of hunting and removal of competing sheep and cattle also had an impact
  • Serengeti plains of eastern Africa
    • Large predators have little effect on large mammal prey
field studies of predator prey interactions121
Field Studies of Predator-Prey Interactions
  • Serengeti plains of eastern Africa (cont.)
    • Most prey taken are either injured or senile
    • Contribute little to future generations
    • Prey are migratory
  • Moose population on Michigan's Isle Royale
field studies of predator prey interactions122
Field Studies of Predator-Prey Interactions
  • Moose population on Michigan's Isle Royale (cont.)
    • Wolf-free existence until 1949.
    • Durwood Allen (1958) began to track wolf and moose populations
    • Trends in populations (Figure 10.8)
slide123

2600

2400

2200

60

2000

Moose

1800

50

1600

1400

40

1200

Moose

Wolves

30

1000

800

20

600

400

10

Wolves

200

0

0

1990

1997

1955

1960

1965

1970

1975

1980

1985

1995

Year

field studies of predator prey interactions124
Field Studies of Predator-Prey Interactions
  • Trends in populations (cont.)
    • Wolf population
      • Peaked at 50 in 1980
      • Severe nosedive in 1981
      • Small recovery in the late 1990s
    • Moose population
      • Increased steadily in the 1960s and 1970s
      • Declined as the wolf population increased until 1981
field studies of predator prey interactions125
Field Studies of Predator-Prey Interactions
  • Moose population (cont.)
    • A record population of 2500 was reached in 1995, when the wolf population was low
    • Good evidence of prey population control by predators
    • Confounded in 1996 when the moose population crashed - starvation
field studies of predator prey interactions126
Field Studies of Predator-Prey Interactions
  • Canada lynx and snowshoe hare
    • Populations show dramatic cyclic oscillations every 9 to 11 years (Figure 10.9)
slide127

Abundance

of lynx

Abundance

of hares

120

200

180

100

160

140

80

120

Abundance of hares (x 1000)

Abundance of lynx (x 1000)

60

100

80

40

60

40

20

20

1850

1860

1870

1880

1890

1900

1910

1920

1930

1940

field studies of predator prey interactions128
Field Studies of Predator-Prey Interactions
  • Canada lynx and snowshoe hare (cont.)
    • Cycle has existed as long as records have existed (over 200 years)
    • An example of intrinsically stable predator-prey relationship
introduced predators129
Introduced Predators
  • Method for determining the effects of predators
  • Dingo predations on kangaroos in Australia
    • Dingo
      • Introduced species
      • Largest Australian carnivore
introduced predators130
Introduced Predators
  • Dingo (cont.)
    • Predator of imported sheep
    • Eliminated from certain areas
      • Spectacular increases in native species
        • 160 fold increase in red kangaroos
        • Over 20 fold increase in emus
introduced predators131
Introduced Predators
  • Dingo (cont.)
    • Effects on feral pigs
      • Shortage of young pigs
      • Considerable impact on recruitment of pigs (Figure 10.10)
slide132

6+

5-6

4-5

3-4

Age class (years)

2-3

1-2

0.5-1

>.05

60

20

40

60

40

20

0

Females (%)

Males (%)

(a) Dingoes present

6+

5-6

4-5

3-4

Age class (years)

2-3

1-2

0.5-1

>.05

60

20

40

60

40

20

0

Males (%)

Females (%)

(a) Dingoes present

introduced predators133
Introduced Predators
  • European foxes and feral cats in Australia
    • Damage domestic livestock
    • Effects when removed (Figure 10.11)
slide134

60

40

Predators shot

No shooting

Mean no. of rabbits per km of transect

20

0

1981

1982

introduced predators135
Introduced Predators
  • Lamprey and the Great Lakes
    • Construction of Wetland Canal allowed lamprey to enter the Great Lakes
    • Dramatic reduction in lake trout (Figure 10.12)
slide136

7

Lake Huron

6

Mean production

5

4

3

2

1

0

Lake Michigan

7

Mean production

6

5

Lake trout production (millions per pound)

4

3

2

1

0

7

Lake Superior

6

5

Mean production

4

3

2

1

0

1930

1935

1940

1945

1950

1955

1960

introduced predators137
Introduced Predators
  • Lamprey and the Great Lakes (cont.)
    • Trout recovered after lamprey population was reduced
field experiments with natural systems138
Field Experiments with Natural Systems
  • Lions in South Africa
    • Kruger National Park, 1903
    • Lions Shot
    • Number of large prey increased
    • Shooting of lions ends, 1960
    • Wildebeast increase so much that their numbers had to be culled from 1965 to 1972
field experiments with natural systems139
Field Experiments with Natural Systems
  • Gray partridge, European game bird
    • Figure 10.13
field experiments with natural systems140
Field Experiments with Natural Systems
  • Gray partridge, European game bird (cont.)
    • Over 20 million shot in Great Britain in the 1930s
    • Only 3.8 million shot in the mid-1980s
      • High chick mortality due to starvation
field experiments with natural systems141
Field Experiments with Natural Systems
  • Only 3.8 million shot in the mid-1980s (cont.)
    • Reduced insects due to introduction of herbicides in the 1950s was suspected
    • However, smaller populations in areas where there was no control of predators by gamekeepers
field experiments with natural systems142
Field Experiments with Natural Systems
  • Only 3.8 million shot in the mid-1980s (cont.)
    • Predation control increased
      • The number of partridges that bred successfully
      • The average size of the broods
      • Partridge populations by 75 %
field experiments with natural systems143
Field Experiments with Natural Systems
  • Predators and rodents in Finland
    • Large scale removal of predators, April 1992 and 1995 over 2-3 km2
    • Large increase in rodent population by June (compared to control plots) (Figure 10.14)
slide144

3.5

3

2.5

Mean number of

rodents per sample

2

1.5

1

Without predators

0.5

0

June

April

3.5

3

2.5

Mean number of

rodents per sample

2

1.5

1

0.5

With predators

0

June

April

applied ecology145
Applied Ecology
  • Humans as predators - whaling
    • Exploitation necessary
    • Is harvesting at any level sustainable?
  • History of Antarctic whaling
    • Figure 1
applied ecology146
Applied Ecology
  • History of Antarctic whaling (cont.)
    • 1930s, blue whales primarily harvested
    • 1950s, blue whale population depleted, replaced with fin whale
    • 1960s, fin whale population collapsed
applied ecology147
Applied Ecology
  • History of Antarctic whaling (cont.)
    • 1960s, humpback whale population collapsed
    • Prior to 1958, Sei whales hardly ever harvested
      • Reduction in other whales made Sei whale attractive
applied ecology148
Applied Ecology
  • Prior to 1958, Sei whales hardly ever harvested (cont.)
    • Peak harvest of about 20,000 by 1964-65
    • Catches declined thereafter due to limitations
  • The relatively small minke whale
    • Was ignored in the southern oceans until 1971-72
applied ecology149
Applied Ecology
  • The relatively small minke whale (cont.)
    • Began to be taken, and is now the largest component of the southern baleen whale catch
  • Whale ban proposed in 1985-86, took effect in 1988
applied ecology150
Applied Ecology
    • Iceland, Norway, and Japan, 1994
      • Argued for resumption of limited commercial whaling
  • Should we ban commercial whaling?
  • Whale populations are recovering
applied ecology151
Applied Ecology
  • Whale populations are recovering (cont.)
    • Ex. Blue whale populations have increased four fold
    • Ex. California grey whales have recovered to prewhaling levels
summary152
Summary
  • Predation is a strong selective force in nature
    • Aposematic coloration
    • Camouflage
    • Batesian and Mullerian mimicry
    • Intimidation displays
    • Polymorphisms
summary153
Summary
  • Predation is a strong selective force in nature (cont.)
    • Chemical defenses
  • Modeling predator-prey interactions
    • Even simple predator-prey models show
summary154
Summary
  • Even simple predator-prey models show (cont.)
    • Stable cycles
    • Wildly increasing and unstable oscillations
  • Difficulty in predicting or modeling how predators and prey interact
    • Mutual interference between predators
summary155
Summary
  • Difficulty in predicting or modeling how predators and prey interact (cont.)
    • Existence of specific predator territory sizes
    • Ability of predators to feed on more than one type of prey
summary156
Summary
  • Large-scale observations support
    • Predators only take weak and sickly individuals
    • Prey populations influence predator numbers, not vice versa
summary157
Summary
  • Accidental or deliberate introductions of exotic predators
    • Profound effects on native prey populations
    • Predators have important regulatory effects on prey
summary158
Summary
  • Accidental or deliberate introductions of exotic predators (cont.)
    • May not be indicative of “natural systems”
summary159
Summary
  • Evidence from natural systems
    • Most studies have concluded that predators have a significant effect on prey
discussion question 1160
Discussion Question #1
  • Should ranchers be concerned about the reintroduction into their vicinity of large predators, like wolves and panthers?
discussion question 2161
Discussion Question #2
  • Do sea lions, otters, or dolphins decrease the stock of fish available for people that fish?
discussion question 3162
Discussion Question #3
  • Would the number of deer available for hunters be the same in the presence of large predators?
discussion question 4163
Discussion Question #4
  • What data would you need to collect to answer the above 3 questions?
discussion question 5164
Discussion Question #5
  • What can the effects of exotic predators tell us about the strength of predation? What can't they tell us?
discussion question 6165
Discussion Question #6
  • Which do you think more likely: that predators control prey populations or that prey control predator populations? Would the answer vary according to the particular system? Give an example.
discussion question 7166
Discussion Question #7
  • What shortcomings do you think Rosenzweig and MacArthur's predator and prey isoclines have? What would these shortcomings mean in terms of determining how predators and prey interact?
discussion question 8167
Discussion Question #8
  • A great many fish stocks seem to have been overfished. How do you think we could prevent overfishing? What biological information do we need to have, and how can we get it when we can't see the population in question?