Chapter 9Chapter 9

Population Dynamics, Carrying Capacity, and Conservation Biology

Population Dynamics, Carrying Capacity, and Conservation Biology

Key QuestionsKey Questions

• How do populations change in size, density, and makeup?

• What is the role of predators in controlling population size?

• What is conservation biology?

• How can we live more sustainably?

• How do populations change in size, density, and makeup?

• What is the role of predators in controlling population size?

• What is conservation biology?

• How can we live more sustainably?

Major Characteristics of a Population

Major Characteristics of a Population

Populations can change in…

1. Size (number of individuals)2. Density (number of individuals in a

certain area)3. Dispersion (spatial pattern)4. Age distribution

Populations can change in…

1. Size (number of individuals)2. Density (number of individuals in a

certain area)3. Dispersion (spatial pattern)4. Age distribution

Clumped(elephants)

Uniform(creosote bush)

Random(dandelions)

DispersionDispersion

These changes are called…These changes are called…

• Population Dynamics!

-occur in response to environmental stress OR changes in environmental conditions

• Population Dynamics!

-occur in response to environmental stress OR changes in environmental conditions

What Limits Population Growth?

What Limits Population Growth?

• Births

• Deaths

• Immigration (to a new area)

• Emigration (out of an area)

Population change = (births + immigration) – (deaths + emigration)

• Births

• Deaths

• Immigration (to a new area)

• Emigration (out of an area)

Population change = (births + immigration) – (deaths + emigration)

PopulationsPopulations

• Populations vary in biotic potential (growth)

• Intrinsic rate of increase (r)-rate at which a population would grow if it had unlimited resources

• Populations vary in biotic potential (growth)

• Intrinsic rate of increase (r)-rate at which a population would grow if it had unlimited resources

High intrinsic rate of increase populations…

High intrinsic rate of increase populations…

• Reproduce early in life

• Short generation times

• Reproduce many times

• Many offspring each time they reproduce

• Reproduce early in life

• Short generation times

• Reproduce many times

• Many offspring each time they reproduce

Example…Example…

• FLIES!-high intrinsic rate of increase/biotic potential

• Without control, there would be 5.6 trillion flies within 13 months

• Within a few years, flies could cover the surface of the earth!

• FLIES!-high intrinsic rate of increase/biotic potential

• Without control, there would be 5.6 trillion flies within 13 months

• Within a few years, flies could cover the surface of the earth!

Of course…Of course…

• This is not realistic because no population can grow indefinitely

• There are always limiting factors!

• This is not realistic because no population can grow indefinitely

• There are always limiting factors!

Environmental ResistanceEnvironmental Resistance

• all limiting factors

• together the biotic potential and environmental resistance determine the carrying capacity

• all limiting factors

• together the biotic potential and environmental resistance determine the carrying capacity

POPULATION SIZE

Growth factors(biotic potential)

Favorable lightFavorable temperatureFavorable chemical environment (optimal level of critical nutrients)

Abiotic

BioticHigh reproductive rate

Generalized niche

Adequate food supply

Suitable habitat

Ability to compete for resources

Ability to hide from or defend against predatorsAbility to resist diseases and parasitesAbility to migrate and live in other habitatsAbility to adapt to environmental change

Decrease factors(environmental resistance)

Too much or too little lightTemperature too high or too lowUnfavorable chemical environment (too much or too little of critical nutrients)

Abiotic

BioticLow reproductive rate

Specialized niche

Inadequate food supply

Unsuitable or destroyed habitat

Too many competitorsInsufficient ability to hide from or defend against predatorsInability to resist diseases and parasitesInability to migrate and live in other habitatsInability to adapt to environmental change

Population SizePopulation Size© 2004 Brooks/Cole – Thomson Learning

A Few More TermsA Few More Terms

• Carrying Capacity (K)-number of individuals that can be sustained in a given space

• Minimum viable population (MVP)-minimum population size needed to support a breeding population (below MVP, extinction is likely)

• Carrying Capacity (K)-number of individuals that can be sustained in a given space

• Minimum viable population (MVP)-minimum population size needed to support a breeding population (below MVP, extinction is likely)

Exponential and Logistic Growth

Exponential and Logistic Growth

• A population has exponential growth when it has few/no resource limitations (J-shaped curve)

• Logistic growth- exponential population growth that approaches carrying capacity and levels off (S-shaped curve)

• A population has exponential growth when it has few/no resource limitations (J-shaped curve)

• Logistic growth- exponential population growth that approaches carrying capacity and levels off (S-shaped curve)

© 2004 Brooks/Cole – Thomson Learning

Time (t) Time (t)

Po

pu

lati

on

siz

e (N

)

Po

pu

lati

on

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e (N

)

K

Exponential Growth Logistic Growth

What Happens If Population Size Exceeds Carrying

Capacity?

What Happens If Population Size Exceeds Carrying

Capacity?

• Overshoot-exceeds carrying capacity• Dieback-happens unless individuals

change resources or move to another area

• Humans are not exempt from this!• Potato fungus in Ireland; 1 million died/3

million emigrated

• Overshoot-exceeds carrying capacity• Dieback-happens unless individuals

change resources or move to another area

• Humans are not exempt from this!• Potato fungus in Ireland; 1 million died/3

million emigrated

2.0

1.5

1.0

.5

Nu

mb

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of

she

ep (

mill

ion

s)

1800 1825 1850 1875 1900 1925

Year

Overshoot

How Does Density Affect Population Growth?

How Does Density Affect Population Growth?

• Density-independent population controls (do NOT depend on size of population): floods, fires, hurricanes, habitat destruction, pesticides

• Density-dependent population controls (depend on size of population): competition, predation, disease, parasitism

• Density-independent population controls (do NOT depend on size of population): floods, fires, hurricanes, habitat destruction, pesticides

• Density-dependent population controls (depend on size of population): competition, predation, disease, parasitism

Population Curves in NaturePopulation Curves in Nature

• Stable: fluctuates slightly above and below carrying capacity (undisturbed areas)

• Irruptive: fairly stable with occasional explosions

• Irregular: chaotic, no recurring pattern • Cyclic: regular cycles

• Stable: fluctuates slightly above and below carrying capacity (undisturbed areas)

• Irruptive: fairly stable with occasional explosions

• Irregular: chaotic, no recurring pattern • Cyclic: regular cycles

Natural Population CurvesNatural Population Curves

Do Predators Control Population Size?

Do Predators Control Population Size?

• YES!• Lynx-Hare Cycle:• Shortage of hares reduces lynx population• Hare population builds up because there

are fewer predators• Lynx population increases because there

are more hares• Cycle begins again

• YES!• Lynx-Hare Cycle:• Shortage of hares reduces lynx population• Hare population builds up because there

are fewer predators• Lynx population increases because there

are more hares• Cycle begins again

Two Ideas About Lynx-Hare Cycle

Two Ideas About Lynx-Hare Cycle

• Top-down control hypothesis: lynx controls hare population

• Bottom-up control hypothesis: hare controls lynx population

• Top-down control hypothesis: lynx controls hare population

• Bottom-up control hypothesis: hare controls lynx population

Po

pu

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siz

e (t

ho

usa

nd

s)

160

140

120

100

80

60

40

20

0

Year

Hare

Lynx

Reproductive Patterns and Survival

Reproductive Patterns and Survival

• Asexual reproduction: all offspring are exact copies (clones) of a single parent

• Sexual reproduction: combination of gametes (97% of species)

• r-selected species

• K-selected species

• Asexual reproduction: all offspring are exact copies (clones) of a single parent

• Sexual reproduction: combination of gametes (97% of species)

• r-selected species

• K-selected species

Reproductive PatternsReproductive Patterns

r-selected: opportunist species; high intrinsic rate of increase; reproduce early; algae, bacteria, rodents, insects

• Many offspring each time they reproduce• Reproduce at young age• Short generation times• Little or no parental care• Short life-spans• Irregular and unstable changes in

population size

r-selected: opportunist species; high intrinsic rate of increase; reproduce early; algae, bacteria, rodents, insects

• Many offspring each time they reproduce• Reproduce at young age• Short generation times• Little or no parental care• Short life-spans• Irregular and unstable changes in

population size

r-Selected Species

cockroach dandelion

Many small offspringLittle or no parental care and protection of offspringEarly reproductive ageMost offspring die before reaching reproductive ageSmall adultsAdapted to unstable climate and environmental conditionsHigh population growth rate (r)Population size fluctuates wildly above and below carrying capacity (K)Generalist nicheLow ability to competeEarly successional species

Reproductive Patterns, continued

Reproductive Patterns, continued

• K-selected: competitor species; mammals, long-lived plants, birds of prey

• Reproduce late in life• Few offspring• Long generation times• Nurture and protect their young• Logistic growth curve

• K-selected: competitor species; mammals, long-lived plants, birds of prey

• Reproduce late in life• Few offspring• Long generation times• Nurture and protect their young• Logistic growth curve

Fewer, larger offspringHigh parental care and protection of offspringLater reproductive ageMost offspring survive to reproductive ageLarger adultsAdapted to stable climate and environmental conditionsLower population growth rate (r)Population size fairly stable and usually close to carrying capacity (K)Specialist nicheHigh ability to competeLate successional species

elephant saguaro

K-Selected Species

Figure 9-9Page 196Figure 9-9Page 196

Nu

mb

er o

f in

div

idu

als

Time

Carrying capacity

K species;experienceK selection

r species;experiencer selection

K

Survivorship CurvesSurvivorship Curves

• Shows the number of survivors of each age group for a species

3 Types:1. Late Loss Curves: high survivorship to a

certain age, then high death rate (elephants, humans)

2. Constant Loss Curves: constant death rate at all ages (songbirds)

3. Early Loss Curves: survivorship is low early in life (r-selected species)

• Shows the number of survivors of each age group for a species

3 Types:1. Late Loss Curves: high survivorship to a

certain age, then high death rate (elephants, humans)

2. Constant Loss Curves: constant death rate at all ages (songbirds)

3. Early Loss Curves: survivorship is low early in life (r-selected species)

Per

cen

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(lo

g s

cale

)100

10

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Age

Conservation BiologyConservation Biology

• Started in the 1970s• Uses science to take action to preserve

species and ecosystems3 principles1. Biodiversity is necessary to all life on earth

and should not be reduced by humans2. Humans should not disrupt vital ecological

processes3. The best way to preserve earth’s

biodiversity is to protect ecosystems

• Started in the 1970s• Uses science to take action to preserve

species and ecosystems3 principles1. Biodiversity is necessary to all life on earth

and should not be reduced by humans2. Humans should not disrupt vital ecological

processes3. The best way to preserve earth’s

biodiversity is to protect ecosystems