chapter 5 life history strategies © 2002 by prentice hall, inc. upper saddle river, nj 07458...

Chapter 5Life History Strategies

© 2002 by Prentice Hall, Inc.

Upper Saddle River, NJ 07458

生活史策略

#2Chapt. 05

Outline• Reproductive strategies

– Species that reproduce throughout their lifetimes (iteroparous 反覆生殖 )

– Species that reproduce just once (semelparous 單次生殖 )

#3Chapt. 05

Outline• Age structure

– Growing populations– Declining populations

• Classification of mating systems

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Outline• Continuum of life history

strategies– r-selected– K-selected– Carrying capacity 承載量

#5Chapt. 05

Life history strategiesFundamental aspects:

1.   Size體型：2.   Metamorphosis變態；3.   Diapause滯育；4.   Senescence衰老；5.   Reproductive patterns繁殖模式；

#6Chapt. 05

Life history strategiesFundamental aspects:

1.   Size體型： The mass and dimensions typical of adult individuals of a species.

2.   Metamorphosis變態；3.   Diapause滯育；4.   Senescence衰老；5.   Reproductive patterns繁殖模式；

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The effects of body size.

體型體表面積附肢

比例

食物、代謝、運動能力

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Life history strategiesFundamental aspects:1.   Size體型：2.   Metamorphosis變態； The presence of a major developmental change in shape of form from the juvenile to the adult.

3.   Diapause滯育；4.   Senescence衰老；5.   Reproductive patterns繁殖模式；

#9Chapt. 05

Life history strategiesFundamental aspects:1.   Size體型：2.   Metamorphosis變態；3.   Diapause滯育； The present of a resting stage in the life history.4.   Senescence衰老；5.   Reproductive patterns繁殖模式；

#10Chapt. 05

Life history strategiesFundamental aspects:1.   Size體型：2.   Metamorphosis變態；3.   Diapause滯育；4.   Senescence衰老； The process and timing of aging, degeneration, and death.5.   Reproductive patterns繁殖模式；

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Senescence衰老

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Life history strategiesFundamental aspects:1.   Size體型：2.   Metamorphosis變態；3.   Diapause滯育；4.   Senescence衰老；5.   Reproductive patterns繁殖模式； The magnitude and timing of reproductive events (clutch size, age at reproductive maturity, size of young, number of reproductive events in a life time, amount of parental investment and care, and the like).

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Reproductive power is limited by two processes:

1. The acquisition of energy, which increases with mass raised to the 0.75power.

2. The rate of conversion of energy to offspring, which changes as a function of mass to the –0.25 power.

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Reproductive Strategies• Semelparity

– Organisms that produce all of their offspring in a single reproductive event.

– May live several years before reproducing or lifespan is one year (ex. Annual plants)

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Reproductive Strategies• Semelparity (cont.).

– Ex. Figure 5.1.

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Reproductive Strategies• Iteroparity

– Organisms that reproduce in successive years or breeding seasons

– Variation in the number of clutches and number of offspring per clutch.

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Reproductive Strategies• Iteroparity (cont.).

– Some species have distinct breeding seasons•Ex. Temperate birds and temperate

forest trees•Lead to distinct generations

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Reproductive Strategies• Iteroparity (cont.).

– Some species reproduce repeatedly and at any time during the year (continuous iteroparity)•Ex. Some tropical species, many

parasites, and humans

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Reproductive Strategies• Environmental Uncertainty

– Favors iteroparity– Survival of juveniles is poor and

unpredictable– Selection favors

•Repeated reproduction•Long reproductive life

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Reproductive Strategies• Environmental Uncertainty

•Spread the risk over a longer period (“bet hedging”)

• Environmental Stable– Favors semelparity

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Reproductive Strategies• Environmental Stable (cont).

– More energy can be devoted to seed production rather than maintenance

– Annuals rely on seed storage during environmentally unstable years

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洄游性鮭魚的產卵策略

陸封型鮭魚的產卵策略又如何？

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Age Structure• Semelparous organisms

– Often produce groups of same-aged young – cohorts

– Cohorts grow at similar rates

• Iteroparous organisms– Many young at different ages

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Age Structure• Increasing populations – large

number of young• Decreasing populations – few

young– Loss of age classes

• Influence on population

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Age Structure– Loss of age classes (cont.).

• Ex. Overexploited fish populations – older age classes

– Reproductive age classes removed– Reproductive failure– Results in population collapse

• Ex. Younger age classes, deer removing young trees

– Figure 5.2

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20

40

60

20

40

60

(a) Age distribution in an undisturbed forest

(b) Age distribution skewed toward adults where overgrazing has reduced the abundanceof young trees

10 20 30 40 50 60 70

Age (years)

Perc

ent

of

trees

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Mating Systems• Sex ratio

– Applied ecology•Hunters prefer deer populations

dominated by males•Effects of too many males on population

growth– Analysis of the ratio

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Mating Systems•Why is the sex ratio usually 1:1?

– Aren’t males superfluous?– Answer: Selfish genes!

» Populations – predominately female

» Populations – predominately male

» Over time, sex ratio would be kept at 1:1

• Selection would favor sons

• Selection would favor daughters

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Mating Systems– Exception to 1:1

•One male dominates in breeding•Occurs in species with

– Low powers of dispersal– Inbreeding is frequent

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Mating Systems•Ex. The parasitic Hymenoptera

– Females mate once and store sperm– Females control sex ratio

» Use sperm to create females» Without sperm to create males

– Process termed haplodiploid

•Ex. The mite Acarophenox (Figure 5.3)

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Mating Systems• Mating systems in animals

– Monogamy•Exclusive mating•Common among birds (~90%) of

species

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Mating Systems– Polygamy

• Individuals mate with multiple partners•Polygyny

– One male mates with multiple females– Females mate with one male

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Mating Systems•Polyandry

– One female mates with multiple males– Males mate with one female

– Polygyny•Females must care for the young•Mammals tend to be polygynous

– Ex. Figure 5.4

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Mating Systems– Polygyny (cont.).

• Influenced by spatial and temporal distribution of females

– Monogamous relationships result from all females becoming sexually receptive at the same time

– Female receptiveness spread over weeks or months – polygyny can result

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Mating Systems•Resource-based polygyny

– Critical resource is patchily distributed or in short supply

– Male can dominate resource and breed with more than one visiting female

– Disadvantages for the female» Must share resources» More females means less success» Figure 5.5

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Number of females per group

1 2 3 4 5 6

1

2

3

4

5

Num

ber

of

yearl

ings

per

male

( )

Num

ber

of

yearl

ings

per

fem

ale

( )

0.5

0.75

1.0

1.25

#37Chapt. 05

Mating Systems•Non-resource based polygyny

– Harem-based» Common in groups or herds» Protection from predators» Harem master does not remain for long

– Communal courting areas – leks» Figure 5.6

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Mating Systems– Polyandry

•Practiced by a few species of birds•Ex. Spotted sandpiper in the Arctic

tundra– Reproductive success not limited by food– Limited by the number of males needed to

incubate eggs.

•Ex. American jacana (Figure 5.7)

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Life History Strategies

• Success of populations– Reproductive strategies– Survival strategies– Habitat usage– Competition with other organisms

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Life History Strategies

– K-Selected•Populations increase slowly toward the

carrying capacity • (K) of the environment•Low reproductive allocations• Iteroparous•High competitive abilities

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Life History Strategies

•Ex. Mature forest– Non-disturbed habitat– Grow slowly– Reach reproductive age late– Devote large amounts of energy to growth

and maintenance

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Life History Strategies

•Ex. Mature forest (cont.).– Grow to large sizes and shade-out r-selected

species– Long-lived and produce seeds repeatedly

every year while mature– Seeds are bigger than r-selected species –

provide food reserves to help them get started

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Life History Strategies

• Alternatives to the r and K continuum– Ruderals, competitors, and stress

tolerators (Grime 1977 and 1979)•Ruderals (botanical term for weed)

– Adapted to cope with habitat disturbances

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Life History Strategies

•Competitors – Adapted to live in highly competitive but

benign environments (e.g., tropics)

•Stress tolerators– Adapted to cope with severe environmental

conditions (e.g., salt marsh plants)

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Life History Strategies

•Stress, disturbance and competition triangle

– Figure 5.9

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CHARACTERISTIC COMPETITORS RUDERALS STRESSTOLERATORS

Life form

Leaf size

Life span

Seed production

Growth rate

Palatability

Vegetative spread

Leaf litter production

Large herbs,shrubs or trees

•Large

•Long

•Small

•Rapid

•Various

•Yes

•High

Small herbs

•Large

•Short

•Large

•Rapid

•High

•No

•Low

Lichens, herbs,shrubs

•Small

•Long

•Small

•Slow

•Low

•Yes

•LowCompetitors

Hig

h Low

Com

petit

ion

Disturbance

HighLo

w

StressLowHigh

RuderalsStress tolerators

Intermediate Life histories

Trees Perennialherbs

Bryophytes

AnnualplantsLichens

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Life History Strategies

•Demographic interpretation (Silverton et al. 1992, 1993)

– Growth-survival and fecundity triangle– Figure 5.10

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G

Gro

wth

Survival

Fecundity

1.0 0.8 0.6 0.4 0.2 0.0

Semelparous herbs

Iteroparous herbs in open habitats

Iteroparous herbs in forests

Woody trees

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

SF

#49Chapt. 05

Applied Ecology

• Life history and the risk of extinction

• K-selected species– All attributes set them at risk to

extinction– Tend to be bigger – need bigger

habitat

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Applied Ecology

• K-selected species (cont.). – Fewer offspring – populations can not

recover as fast from disturbance– Breed later in life – generation time is

long

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Applied Ecology

• K-selected species (cont.). – Population size is small – high risk of

inbreeding– Examples

•Florida panthers•Giant sequoia tree

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Applied Ecology

– Examples (cont.).•Large terrestrial mammals (elephants,

rhinoceros, and grizzlies)•Large marine mammals (blue and sperm

whales)

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Summary

• Life history concerns lifetime patterns in reproduction and growth patterns– Semelparous– Iteroparous

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Summary

• Reproductive strategy strongly affects age structure– Low ratio of young to adults –

population in decline– High ratio of young to adults –

population growing

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Summary

• Sex ratio– 1:1 ratio expected in most

populations– Polygynous

•Males mate with more than one female

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Summary

• Sex ratio– Polyandrous

•Females mate with more than one male•Monogamous

– Each individual has one mate

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Summary– Polygamy is often based on limited

resources

• Categorizing life history strategies– r-K continuum

• r-selected– Poor competitors

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Summary• r-selected (cont.).

– High per capita population growth rate– Disperse well– Colonize new habitats

•K-Selected– Good competitors– Usually exist in mature habitats, close to the

carrying capacity

– Alternative life history strategies

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Summary

– Alternative life history strategies•Ruderals, competitors, and stress

tolerators classification•Growth-longevity-fecundity triangle

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Discussion Question #1

• What particular life history strategies are possessed by successful exotic invaders like kudzu in the southeast or zebra mussels in the Great Lakes? Can knowing their life histories help us in the war against exotics?

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Discussion Question #2

• How could you test the idea that there is a trade-off between life history strategies? What would happen if you plant salt marsh plants like Spartina grass or mangroves in a terrestrial habitat vs. a freshwater habitat?

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Discussion Question #3

• In some species, males are much bigger than females, a property called sexual dimorphism. Speculate about the types of animals in which sexual dimorphism would and would not occur.