chapter 10 predation © 2002 by prentice hall, inc. upper saddle river, nj 07458
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Chapter 10Predation
© 2002 by Prentice Hall, Inc.
Upper Saddle River, NJ 07458
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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
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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
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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
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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.
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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。
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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
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Density independent factor
. 氣候因素
. 土壤因素
. 營養
. 理化
. 空間
. 汙染
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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
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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
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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
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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
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Introduction• Predation (cont.)
– Predator-prey associations•Figure 10.2
Inti
macy
Low
Hig
h
Parasite Parasitoids
Grazer PredatorLethality HighLow
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Antipredator Adaptations• Aposematic or warning coloration
– Advertises an unpalatable taste– Ex. Blue jays and monarch butterflies
•Caterpillar obtains poison from milkweed
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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
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Antipredator Adaptations• Camouflage
– Blending of organism into background color
– Grasshoppers (Figure 10.3b)
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Antipredator Adaptations• Camouflage (cont.)
– Stick insects mimic twigs and branches
– Zebra stripes: blend into grassy background
• Mimicry
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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
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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
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Antipredator Adaptations•Batesian mimicry (cont.)
– Ex. hoverflies resemble stinging bees and wasps (Figure 10.3d)
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Antipredator Adaptations•Difficulty distinguishing type of mimicry
– Monarch butterflies and viceroy butterflies (Figures 10.3d,e)
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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)
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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
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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
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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
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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”
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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
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Antipredator Adaptations• Masting (cont.)
– Satiate predators– Allows for some progeny to survive– Common to seed herbivory– Ex. 17-year and 13-year periodical
cicadas
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Antipredator Adaptations• Comparison of defense
mechanisms– Table 10.1, chemical defense is most
common
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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
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Predator-Prey Models• Graphical method to monitor
relationship (cont.)– Prey isoclines have characteristic
hump shape•Figure 10.4
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Prey increase
i) Prey iscoline
K N
N
N
N
K
1 1
1
2
2
2
ii) Predator iscoline
Prey density
Predator increasesPredator decreases
Pre
dato
r densi
tyPre
dato
r densi
ty
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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
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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
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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
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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
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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)
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Damped oscillations
Preyisocline
Predatorisocline
a)
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Predator-Prey Models•Three general cases (cont.)
– A moderately efficient predator leads to stable oscillations of predator and prey populations (Figure 10.5b)
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Stable oscillations
Popula
tion d
ensi
ty
Predator equilibrium density
b)
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Predator-Prey Models•Three general cases (cont.)
– A highly efficient predator can exploit a prey nearly down to its limiting rareness (Figure 10.5c)
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Increasing oscillations
Pre
dato
r dens i
t y
c)
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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)
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K1 increases to K1* with enrichment
Prey
PredatorPredator isocline remains unchanged
“The paradox of enrichment”
Prey isoclinechanges
K1 K1*
d)
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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
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Predator-Prey Models• Functional response
– How an individual predator responds to prey density can affect how predators interact with prey (Figure 10.6)
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I
II
III
Num
ber
of
pre
y e
ate
n p
er
pre
dato
r
Prey density
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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.
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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)
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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
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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)
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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)
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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
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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
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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)
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60
0
10
20
30
40
50
Wolv
es
1955 1960 1965 1970 1975 1980 1985 1990 1995 1997
Moose
Wolves
Year
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
Moose
0
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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
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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
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Field Studies of Predator-Prey Interactions
– Canada lynx and snowshoe hare•Populations show dramatic cyclic
oscillations every 9 to 11 years (Figure 10.9)
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20
40
60
80
100
120
20
40
60
80100120
140
160180
200Abundance
of lynxAbundance
of hares
Abundance
of
lynx (
x 1
00
0)
Abundance
of
hare
s (x
10
00
)
1850 1860 1870 1880 1890 1900 1910 1920 1930 1940
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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
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Introduced Predators• Method for determining the
effects of predators• Dingo predations on kangaroos in
Australia– Dingo
• Introduced species•Largest Australian carnivore
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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
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Introduced Predators– Dingo (cont.)
•Effects on feral pigs– Shortage of young pigs– Considerable impact on recruitment of pigs
(Figure 10.10)
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060 40 20 20 40 60
Age c
lass
(years
)
Males (%) Females (%)
060 40 20 20 40 60
Males (%) Females (%)
6+5-6
4-5
3-42-3
1-20.5-1
>.05
6+5-6
4-5
3-4
2-31-2
0.5-1
>.05
Age c
lass
(years
)
(a) Dingoes present
(a) Dingoes present
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Introduced Predators• European foxes and feral cats in
Australia– Damage domestic livestock– Effects when removed (Figure 10.11)
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0
20
40
60
Predators shot
No shooting
1981 1982
Mean n
o. of
rabbit
s per
km o
f tr
anse
ct
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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)
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Lake Huron
Mean production
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
10
Lake Michigan
Lake Superior
Mean production
Mean production
1930 1935 1940 1945 1950 1955 1960
Lake
tro
ut
pro
duct
ion (
mill
ions
per
pound)
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Introduced Predators• Lamprey and the Great Lakes
(cont.)– Trout recovered after lamprey
population was reduced
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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
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Field Experiments with Natural Systems
• Gray partridge, European game bird– Figure 10.13
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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
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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
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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 %
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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)
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April June
April June
3.5
3
2.5
2
1.5
1
0.5
0
3.5
3
2.5
2
1.5
1
0.5
0
Without predators
With predators
Mean n
um
ber
of
rodents
per
sam
ple
Mean n
um
ber
of
rodents
per
sam
ple
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Applied Ecology• Humans as predators - whaling
– Exploitation necessary– Is harvesting at any level
sustainable?
• History of Antarctic whaling– Figure 1
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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
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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
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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
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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
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Applied Ecology– Iceland, Norway, and Japan, 1994
•Argued for resumption of limited commercial whaling
• Should we ban commercial whaling?
• Whale populations are recovering
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Applied Ecology• Whale populations are recovering
(cont.)– Ex. Blue whale populations have
increased four fold– Ex. California grey whales have
recovered to prewhaling levels
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Summary• Predation is a strong selective
force in nature– Aposematic coloration– Camouflage– Batesian and Mullerian mimicry– Intimidation displays– Polymorphisms
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Summary• Predation is a strong selective
force in nature (cont.)– Chemical defenses
• Modeling predator-prey interactions– Even simple predator-prey models
show
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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
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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
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Summary• Large-scale observations support
– Predators only take weak and sickly individuals
– Prey populations influence predator numbers, not vice versa
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Summary• Accidental or deliberate
introductions of exotic predators– Profound effects on native prey
populations– Predators have important regulatory
effects on prey
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Summary• Accidental or deliberate
introductions of exotic predators (cont.)– May not be indicative of “natural
systems”
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Summary• Evidence from natural systems
– Most studies have concluded that predators have a significant effect on prey
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Discussion Question #1• Should ranchers be concerned
about the reintroduction into their vicinity of large predators, like wolves and panthers?
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Discussion Question #2• Do sea lions, otters, or dolphins
decrease the stock of fish available for people that fish?
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Discussion Question #3• Would the number of deer
available for hunters be the same in the presence of large predators?
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Discussion Question #4• What data would you need to
collect to answer the above 3 questions?
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Discussion Question #5• What can the effects of exotic
predators tell us about the strength of predation? What can't they tell us?
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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.
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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?
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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?
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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
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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
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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)
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Damped oscillations
Preyisocline
Predatorisocline
a)
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Predator-Prey Models•Three general cases (cont.)
– A moderately efficient predator leads to stable oscillations of predator and prey populations (Figure 10.5b)
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Stable oscillations
Popula
tion d
ensi
ty
Predator equilibrium density
b)
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Predator-Prey Models•Three general cases (cont.)
– A highly efficient predator can exploit a prey nearly down to its limiting rareness (Figure 10.5c)
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Increasing oscillations
Pre
dato
r dens i
t y
c)
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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)
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K1 increases to K1* with enrichment
Prey
PredatorPredator isocline remains unchanged
“The paradox of enrichment”
Prey isoclinechanges
K1 K1*
d)
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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
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Predator-Prey Models• Functional response
– How an individual predator responds to prey density can affect how predators interact with prey (Figure 10.6)
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I
II
III
Num
ber
of
pre
y e
ate
n p
er
pre
dato
r
Prey density
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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.
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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)
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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
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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)
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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)
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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
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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
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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)
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60
0
10
20
30
40
50
Wolv
es
1955 1960 1965 1970 1975 1980 1985 1990 1995 1997
Moose
Wolves
Year
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
Moose
0
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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
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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
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Field Studies of Predator-Prey Interactions
– Canada lynx and snowshoe hare•Populations show dramatic cyclic
oscillations every 9 to 11 years (Figure 10.9)
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20
40
60
80
100
120
20
40
60
80100120
140
160180
200Abundance
of lynxAbundance
of hares
Abundance
of
lynx (
x 1
00
0)
Abundance
of
hare
s (x
10
00
)
1850 1860 1870 1880 1890 1900 1910 1920 1930 1940
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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
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Introduced Predators• Method for determining the
effects of predators• Dingo predations on kangaroos in
Australia– Dingo
• Introduced species•Largest Australian carnivore
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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
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Introduced Predators– Dingo (cont.)
•Effects on feral pigs– Shortage of young pigs– Considerable impact on recruitment of pigs
(Figure 10.10)
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060 40 20 20 40 60
Age c
lass
(years
)
Males (%) Females (%)
060 40 20 20 40 60
Males (%) Females (%)
6+5-6
4-5
3-42-3
1-20.5-1
>.05
6+5-6
4-5
3-4
2-31-2
0.5-1
>.05
Age c
lass
(years
)
(a) Dingoes present
(a) Dingoes present
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Introduced Predators• European foxes and feral cats in
Australia– Damage domestic livestock– Effects when removed (Figure 10.11)
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0
20
40
60
Predators shot
No shooting
1981 1982
Mean n
o. of
rabbit
s per
km o
f tr
anse
ct
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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)
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Lake Huron
Mean production
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
10
Lake Michigan
Lake Superior
Mean production
Mean production
1930 1935 1940 1945 1950 1955 1960
Lake
tro
ut
pro
duct
ion (
mill
ions
per
pound)
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Introduced Predators• Lamprey and the Great Lakes
(cont.)– Trout recovered after lamprey
population was reduced
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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
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Field Experiments with Natural Systems
• Gray partridge, European game bird– Figure 10.13
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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
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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
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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 %
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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)
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April June
April June
3.5
3
2.5
2
1.5
1
0.5
0
3.5
3
2.5
2
1.5
1
0.5
0
Without predators
With predators
Mean n
um
ber
of
rodents
per
sam
ple
Mean n
um
ber
of
rodents
per
sam
ple
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Applied Ecology• Humans as predators - whaling
– Exploitation necessary– Is harvesting at any level
sustainable?
• History of Antarctic whaling– Figure 1
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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
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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
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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
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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
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Applied Ecology– Iceland, Norway, and Japan, 1994
•Argued for resumption of limited commercial whaling
• Should we ban commercial whaling?
• Whale populations are recovering
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Applied Ecology• Whale populations are recovering
(cont.)– Ex. Blue whale populations have
increased four fold– Ex. California grey whales have
recovered to prewhaling levels
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Summary• Predation is a strong selective
force in nature– Aposematic coloration– Camouflage– Batesian and Mullerian mimicry– Intimidation displays– Polymorphisms
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Summary• Predation is a strong selective
force in nature (cont.)– Chemical defenses
• Modeling predator-prey interactions– Even simple predator-prey models
show
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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
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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
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Summary• Large-scale observations support
– Predators only take weak and sickly individuals
– Prey populations influence predator numbers, not vice versa
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Summary• Accidental or deliberate
introductions of exotic predators– Profound effects on native prey
populations– Predators have important regulatory
effects on prey
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Summary• Accidental or deliberate
introductions of exotic predators (cont.)– May not be indicative of “natural
systems”
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Summary• Evidence from natural systems
– Most studies have concluded that predators have a significant effect on prey
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Discussion Question #1• Should ranchers be concerned
about the reintroduction into their vicinity of large predators, like wolves and panthers?
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Discussion Question #2• Do sea lions, otters, or dolphins
decrease the stock of fish available for people that fish?
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Discussion Question #3• Would the number of deer
available for hunters be the same in the presence of large predators?
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Discussion Question #4• What data would you need to
collect to answer the above 3 questions?
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Discussion Question #5• What can the effects of exotic
predators tell us about the strength of predation? What can't they tell us?
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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.
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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?
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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?