Chapter 8Chapter 8

Population EcologyPopulation Ecology

Chapter Overview QuestionsChapter Overview Questions

What are the major characteristics of What are the major characteristics of populations?populations?

How do populations respond to changes in How do populations respond to changes in environmental conditions?environmental conditions?

How do species differ in their reproductive How do species differ in their reproductive patterns?patterns?

Updates OnlineUpdates Online

The latest references for topics covered in this section can be found at The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. www.thomsonedu.com to access InfoTrac articles.

InfoTrac: One Hatchling at a Time. InfoTrac: One Hatchling at a Time. Brownsville HeraldBrownsville Herald (Brownsville, TX), July 2, 2006.(Brownsville, TX), July 2, 2006.

InfoTrac: Where the Cattle Herds Roam, Ideally in Harmony InfoTrac: Where the Cattle Herds Roam, Ideally in Harmony With Their Neighbors. Jim Robbins. With Their Neighbors. Jim Robbins. The New York TimesThe New York Times, , July 11, 2006 pF3(L).July 11, 2006 pF3(L).

InfoTrac: A nudge for nature. InfoTrac: A nudge for nature. Milwaukee Journal SentinelMilwaukee Journal Sentinel, , July 10, 2006.July 10, 2006.

Earth Island InstituteEarth Island Institute Environmental Defense: Creating a Conservation Environmental Defense: Creating a Conservation

Community inCommunity inOregon’s Williamette ValleyOregon’s Williamette Valley

Marine Bio: Habitat ConservationMarine Bio: Habitat Conservation

They were over-They were over-hunted to the hunted to the brink of extinction brink of extinction by the early by the early 1900’s and are 1900’s and are now making a now making a comeback.comeback.

Core Case Study: Core Case Study: Southern Sea Otters: Are They Back Southern Sea Otters: Are They Back

from the Brink of Extinction?from the Brink of Extinction?

Figure 8-1Figure 8-1

Core Case Study: Core Case Study: Southern Sea Otters: Are They Back Southern Sea Otters: Are They Back

from the Brink of Extinction?from the Brink of Extinction?

Sea otters are an Sea otters are an important important keystone species keystone species for sea urchins for sea urchins and other kelp-and other kelp-eating organisms.eating organisms.

Figure 8-1Figure 8-1

POPULATION DYNAMICS AND POPULATION DYNAMICS AND CARRYING CAPACITYCARRYING CAPACITY

Most populations live in clumps although other Most populations live in clumps although other patterns occur based on resource distribution.patterns occur based on resource distribution.

Figure 8-2Figure 8-2

Fig. 8-2a, p. 162(a) Clumped (elephants)

Fig. 8-2b, p. 162(b) Uniform (creosote bush)

Fig. 8-2c, p. 162(c) Random (dandelions)

Changes in Population Size: Changes in Population Size: Entrances and ExitsEntrances and Exits

Populations increase through births and Populations increase through births and immigrationimmigration

Populations decrease through deaths and Populations decrease through deaths and emigrationemigration

Age Structure: Young Populations Age Structure: Young Populations Can Grow FastCan Grow Fast

How fast a population grows or declines How fast a population grows or declines depends on its age structure.depends on its age structure. Prereproductive agePrereproductive age: not mature enough to : not mature enough to

reproduce.reproduce. Reproductive ageReproductive age: those capable of : those capable of

reproduction.reproduction. Postreproductive agePostreproductive age: those too old to : those too old to

reproduce.reproduce.

Limits on Population Growth: Limits on Population Growth: Biotic Potential vs. Environmental Biotic Potential vs. Environmental

ResistanceResistance

No population can increase its size No population can increase its size indefinitely.indefinitely. The intrinsic rate of increase (The intrinsic rate of increase (rr) is the rate at ) is the rate at

which a population would grow if it had unlimited which a population would grow if it had unlimited resources.resources.

Carrying capacity (Carrying capacity (KK): the maximum population ): the maximum population of a given species that a particular habitat can of a given species that a particular habitat can sustain indefinitely without degrading the habitat.sustain indefinitely without degrading the habitat.

Exponential and Logistic Population Exponential and Logistic Population Growth: J-Curves and S-CurvesGrowth: J-Curves and S-Curves

Populations Populations grow rapidly with grow rapidly with ample ample resources, but resources, but as resources as resources become limited, become limited, its growth rate its growth rate slows and levels slows and levels off.off.

Figure 8-4Figure 8-4

Fig. 8-3, p. 163

EnvironmentalResistance

Time (t)

Po

pu

lat i

on

si z

e (N

)

Carrying capacity (K)

ExponentialGrowth

BioticPotential

Animation: Exponential GrowthAnimation: Exponential Growth

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Exponential and Logistic Population Exponential and Logistic Population Growth: J-Curves and S-CurvesGrowth: J-Curves and S-Curves

As a population As a population levels off, it levels off, it often fluctuates often fluctuates slightly above slightly above and below the and below the carrying carrying capacity.capacity.

Figure 8-4Figure 8-4

Fig. 8-4, p. 164

Carrying capacity

Year

Nu

mb

er o

f sh

eep

(m

illi

on

s)Overshoot

Exceeding Carrying Capacity: Move, Exceeding Carrying Capacity: Move, Switch Habits, or Decline in SizeSwitch Habits, or Decline in Size

Members of Members of populations which populations which exceed their exceed their resources will die resources will die unless they adapt or unless they adapt or move to an area with move to an area with more resources.more resources.

Figure 8-6Figure 8-6

Fig. 8-6, p. 165

Nu

mb

er o

f re

ind

eer

Populationovershootscarryingcapacity

Carryingcapacity

Year

PopulationCrashes

Exceeding Carrying Capacity: Move, Exceeding Carrying Capacity: Move, Switch Habits, or Decline in SizeSwitch Habits, or Decline in Size

Over time species may increase their Over time species may increase their carrying capacity by developing adaptations.carrying capacity by developing adaptations.

Some species maintain their carrying Some species maintain their carrying capacity by migrating to other areas.capacity by migrating to other areas.

So far, technological, social, and other So far, technological, social, and other cultural changes have extended the earth’s cultural changes have extended the earth’s carrying capacity for humans.carrying capacity for humans.

How Would You Vote?How Would You Vote?

Can we continue to expand the earth's Can we continue to expand the earth's carrying capacity for humans?carrying capacity for humans? a. No. Unless humans voluntarily control their a. No. Unless humans voluntarily control their

population and conserve resources, nature will population and conserve resources, nature will do it for us.do it for us.

b. Yes. New technologies and strategies will b. Yes. New technologies and strategies will allow us to further delay exceeding the earth's allow us to further delay exceeding the earth's carrying capacity.carrying capacity.

Population Density and Population Population Density and Population Change: Effects of CrowdingChange: Effects of Crowding

Population density: the number of individuals Population density: the number of individuals in a population found in a particular area or in a population found in a particular area or volume.volume. A population’s density can affect how rapidly it A population’s density can affect how rapidly it

can grow or decline.can grow or decline.• e.g. biotic factors like diseasee.g. biotic factors like disease

Some population control factors are not affected Some population control factors are not affected by population density.by population density.• e.g. abiotic factors like weathere.g. abiotic factors like weather

Types of Population Change Types of Population Change Curves in NatureCurves in Nature

Population sizes may stay the same, increase, Population sizes may stay the same, increase, decrease, vary in regular cycles, or change decrease, vary in regular cycles, or change erratically.erratically. StableStable: fluctuates slightly above and below carrying : fluctuates slightly above and below carrying

capacity.capacity. IrruptiveIrruptive: populations explode and then crash to a : populations explode and then crash to a

more stable level.more stable level. CyclicCyclic: populations fluctuate and regular cyclic or : populations fluctuate and regular cyclic or

boom-and-bust cycles.boom-and-bust cycles. IrregularIrregular: erratic changes possibly due to chaos or : erratic changes possibly due to chaos or

drastic change. drastic change.

Types of Population Change Types of Population Change Curves in NatureCurves in Nature

Population sizes often vary in regular cycles Population sizes often vary in regular cycles when the predator and prey populations are when the predator and prey populations are controlled by the scarcity of resources.controlled by the scarcity of resources.

Figure 8-7Figure 8-7

Fig. 8-7, p. 166

Po

pu

lati

on

siz

e (t

ho

usa

nd

s)

Year

LynxHare

Animation: Capture-Recapture Animation: Capture-Recapture Method Method

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Case Study: Exploding White-Tailed Case Study: Exploding White-Tailed Deer Populations in the United StatesDeer Populations in the United States

Since the 1930s the white-tailed deer Since the 1930s the white-tailed deer population has exploded in the United States.population has exploded in the United States. Nearly extinct prior to their protection in 1920’s.Nearly extinct prior to their protection in 1920’s.

Today 25-30 million white-tailed deer in U.S. Today 25-30 million white-tailed deer in U.S. pose human interaction problems.pose human interaction problems. Deer-vehicle collisions (1.5 million per year).Deer-vehicle collisions (1.5 million per year). Transmit disease (Lyme disease in deer ticks).Transmit disease (Lyme disease in deer ticks).

REPRODUCTIVE PATTERNSREPRODUCTIVE PATTERNS

Some species reproduce without having sex Some species reproduce without having sex (asexual).(asexual). Offspring are exact genetic copies (clones).Offspring are exact genetic copies (clones).

Others reproduce by having sex (sexual).Others reproduce by having sex (sexual). Genetic material is mixture of two individuals.Genetic material is mixture of two individuals. Disadvantages: males do not give birth, increase Disadvantages: males do not give birth, increase

chance of genetic errors and defects, courtship chance of genetic errors and defects, courtship and mating rituals can be costly.and mating rituals can be costly.

Major advantages: genetic diversity, offspring Major advantages: genetic diversity, offspring protection.protection.

Sexual Reproduction: CourtshipSexual Reproduction: Courtship

Courtship rituals Courtship rituals consume time and consume time and energy, can transmit energy, can transmit disease, and can disease, and can inflict injury on males inflict injury on males of some species as of some species as they compete for they compete for sexual partners.sexual partners.

Figure 8-8Figure 8-8

Reproductive Patterns:Reproductive Patterns:Opportunists and CompetitorsOpportunists and Competitors

Large number of Large number of smaller offspring with smaller offspring with little parental care (r-little parental care (r-selected species).selected species).

Fewer, larger Fewer, larger offspring with higher offspring with higher invested parental invested parental care (K-selected care (K-selected species).species).

Figure 8-9Figure 8-9

Fig. 8-9, p. 168

r species;experiencer selection

Time

Nu

mb

er o

f in

div

idu

als

KCarrying capacity

K species;experienceK selection

Reproductive PatternsReproductive Patterns

r-selected species tend to be opportunists r-selected species tend to be opportunists while K-selected species tend to be while K-selected species tend to be competitors.competitors.

Figure 8-10Figure 8-10

Fig. 8-10a, p. 168

Many small offspring

Little or no parental care and protection of offspring

Early reproductive age

Most offspring die before reaching reproductive age

Small adults

Adapted to unstable climate and environmental conditions

High population growth rate (r)

Population size fluctuates wildly above and below carrying capacity (K)

Generalist niche

Low ability to compete

Early successional species

r-Selected SpeciesCockroach

Dandelion

Fig. 8-10b, p. 168

Fewer, larger offspring

High parental care and protection of offspring

Later reproductive age

Most offspring survive to reproductive age

Larger adults

Adapted to stable climate and environmental conditions

Lower population growth rate (r)

Population size fairly stable and usually close to carrying capacity (K)

Specialist niche

High ability to compete

Late successional species

K-Selected Species

SaguaroElephant

Survivorship Curves: Survivorship Curves: Short to Long LivesShort to Long Lives

The way to represent the age structure of a The way to represent the age structure of a population is with a population is with a survivorship curvesurvivorship curve.. Late loss populationLate loss population live to an old age. live to an old age. Constant loss populationConstant loss population die at all ages. die at all ages. Most members of Most members of early loss populationearly loss population, die at , die at

young ages.young ages.

Survivorship Curves: Survivorship Curves: Short to Long LivesShort to Long Lives

The populations The populations of different of different species vary in species vary in how long how long individual individual members typically members typically live.live.

Figure 8-11Figure 8-11

Fig. 8-11, p. 169

Per

cen

tag

e su

rviv

ing

(lo

g s

cale

)

Age

Early loss

Late loss

Constant loss

Animation: Life History PatternsAnimation: Life History Patterns

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Video: Coral SpawningVideo: Coral Spawning

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Video: Kelp Forest (Channel Islands)Video: Kelp Forest (Channel Islands)

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Video: Salmons Swimming UpstreamVideo: Salmons Swimming Upstream

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