chapter 10 predation © 2002 by prentice hall, inc. upper saddle river, nj 07458

Chapter 10Predation

© 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

• Field data suggests that predators have a large impact on prey populations

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

•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

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 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。

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

. 氣候因素

. 土壤因素

. 營養

. 理化

. 空間

. 汙染

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

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• 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

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

Introduction• Predation (cont.)

– Predator-prey associations•Figure 10.2

Inti

macy

Low

Hig

h

Parasite Parasitoids

Grazer PredatorLethality HighLow

Antipredator Adaptations• Aposematic or warning coloration

– Advertises an unpalatable taste– Ex. Blue jays and monarch butterflies

•Caterpillar obtains poison from milkweed

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 Adaptations• Camouflage

– Blending of organism into background color

– Grasshoppers (Figure 10.3b)

Antipredator Adaptations• Camouflage (cont.)

– Stick insects mimic twigs and branches

– Zebra stripes: blend into grassy background

• Mimicry

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 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 Adaptations•Batesian mimicry (cont.)

– Ex. hoverflies resemble stinging bees and wasps (Figure 10.3d)

Antipredator Adaptations•Difficulty distinguishing type of mimicry

– Monarch butterflies and viceroy butterflies (Figures 10.3d,e)

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 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 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 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 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 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 Adaptations• Masting (cont.)

– Satiate predators– Allows for some progeny to survive– Common to seed herbivory– Ex. 17-year and 13-year periodical

cicadas

Antipredator Adaptations• Comparison of defense

mechanisms– Table 10.1, chemical defense is most

common

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 Models• Graphical method to monitor

relationship (cont.)– Prey isoclines have characteristic

hump shape•Figure 10.4

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

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


hump shape (cont.)•Between these two values, prey

population can either increase or decrease depending on predator density

•Above the isocline, prey populations decline


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 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 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)

Damped oscillations

Preyisocline

Predatorisocline

a)

Predator-Prey Models•Three general cases (cont.)

– A moderately efficient predator leads to stable oscillations of predator and prey populations (Figure 10.5b)

Stable oscillations

Popula

tion d

ensi

ty

Predator equilibrium density

b)


– A highly efficient predator can exploit a prey nearly down to its limiting rareness (Figure 10.5c)

Increasing oscillations

Pre

dato

r dens i

t y

c)

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)

K1 increases to K1* with enrichment

Prey

PredatorPredator isocline remains unchanged

“The paradox of enrichment”

Prey isoclinechanges

K1 K1*

d)

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 Models• Functional response

– How an individual predator responds to prey density can affect how predators interact with prey (Figure 10.6)

I

II

III

Num

ber

of

pre

y e

ate

n p

er

pre

dato

r

Prey density

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 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 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 comparisons to models• Do predators control prey

populations?• Importance of predators in

controlling prey density– Kaibab deer herd

•Kaibab Plateau (Northern Arizona)


– 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)


•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


– 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


– 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)

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


•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


– 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


– Canada lynx and snowshoe hare•Populations show dramatic cyclic

oscillations every 9 to 11 years (Figure 10.9)

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


– 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• Method for determining the

effects of predators• Dingo predations on kangaroos in

Australia– Dingo

• Introduced species•Largest Australian carnivore

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


•Effects on feral pigs– Shortage of young pigs– Considerable impact on recruitment of pigs

(Figure 10.10)

060 40 20 20 40 60

Age c

lass

(years

)

Males (%) Females (%)

060 40 20 20 40 60


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

Introduced Predators• European foxes and feral cats in

Australia– Damage domestic livestock– Effects when removed (Figure 10.11)

0

20

40

60

Predators shot

No shooting

1981 1982

Mean n

o. of

rabbit

s per

km o

f tr

anse

ct

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)

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)


(cont.)– Trout recovered after lamprey

population was reduced

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


• Gray partridge, European game bird– Figure 10.13


• 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


– 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


– 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 %


• 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)

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

Applied Ecology• Humans as predators - whaling

– Exploitation necessary– Is harvesting at any level

sustainable?

• History of Antarctic whaling– Figure 1

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


(cont.)– 1960s, humpback whale population

collapsed– Prior to 1958, Sei whales hardly ever

harvested•Reduction in other whales made Sei

whale attractive

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 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 Ecology– Iceland, Norway, and Japan, 1994

•Argued for resumption of limited commercial whaling

• Should we ban commercial whaling?

• Whale populations are recovering

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• Predation is a strong selective

force in nature– Aposematic coloration– Camouflage– Batesian and Mullerian mimicry– Intimidation displays– Polymorphisms


force in nature (cont.)– Chemical defenses

• Modeling predator-prey interactions– Even simple predator-prey models

show

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

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

Summary• Large-scale observations support

– Predators only take weak and sickly individuals

– Prey populations influence predator numbers, not vice versa

Summary• Accidental or deliberate

introductions of exotic predators– Profound effects on native prey

populations– Predators have important regulatory

effects on prey


introductions of exotic predators (cont.)– May not be indicative of “natural

systems”

Summary• Evidence from natural systems

– Most studies have concluded that predators have a significant effect on prey

Discussion Question #1• Should ranchers be concerned

about the reintroduction into their vicinity of large predators, like wolves and panthers?

Discussion Question #2• Do sea lions, otters, or dolphins

decrease the stock of fish available for people that fish?

Discussion Question #3• Would the number of deer

available for hunters be the same in the presence of large predators?

Discussion Question #4• What data would you need to

collect to answer the above 3 questions?

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• 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• 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• 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?


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 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 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)

Damped oscillations

Preyisocline

Predatorisocline

a)


– A moderately efficient predator leads to stable oscillations of predator and prey populations (Figure 10.5b)