Transcript No Population Can Grow Indefinitely

Biodiversity, Species Interactions,
and Population Control
Chapter 5
Core Case Study: Southern Sea Otters: Are
They Back from the Brink of Extinction?
 Habitat
 Hunted: early 1900s
 Partial recovery
 Why care about sea otters?
• Ethics
• Keystone species
• Tourism dollars
Southern Sea Otter
5-1 How Do Species Interact?
 Concept 5-1 Five types of species
interactions—competition, predation, parasitism,
mutualism, and commensalism—affect the
resource use and population sizes of the
species in an ecosystem.
Species Interact in Five Major Ways
 Interspecific Competition
 Predation
 Parasitism
 Mutualism
 Commensalism
Most Species Compete with One Another
for Certain Resources
 Competition
 Competitive exclusion principle
Most Consumer Species Feed on Live
Organisms of Other Species (1)
 Predators may capture prey by
• Walking
• Swimming
• Flying
• Pursuit and ambush
• Camouflage
• Chemical warfare
Most Consumer Species Feed on Live
Organisms of Other Species (2)
 Prey may avoid capture by
• Camouflage
• Chemical warfare
• Warning coloration
• Mimicry
• Deceptive looks
• Deceptive behavior
Some Ways Prey Species Avoid
Their Predators
Science Focus: Why Should We Care
about Kelp Forests?
 Kelp forests: biologically diverse marine habitat
 Major threats to kelp forests
• Sea urchins
• Pollution from water run-off
• Global warming
Purple Sea Urchin
Predator and Prey Species Can Drive
Each Other’s Evolution
 Intense natural selection pressures between
predator and prey populations
 Coevolution
Coevolution: A Langohrfledermaus
Bat Hunting a Moth
Some Species Feed off Other Species by
Living on or in Them
 Parasitism
 Parasite-host interaction may lead to coevolution
Parasitism: Tree with Parasitic Mistletoe,
Trout with Blood-Sucking Sea Lampreys
In Some Interactions, Both Species
Benefit
 Mutualism
 Nutrition and protection relationship
 Gut inhabitant mutualism
Mutualism: Oxpeckers Clean Rhinoceros;
Anemones Protect and Feed Clownfish
In Some Interactions, One Species
Benefits and the Other Is Not Harmed
 Commensalism
 Epiphytes
 Birds nesting in trees
Commensalism: Bromiliad Roots on Tree
Trunk Without Harming Tree
5-2 How Can Natural Selection Reduce
Competition between Species?
 Concept 5-2 Some species develop
adaptations that allow them to reduce or avoid
competition with other species for resources.
Some Species Evolve Ways to Share
Resources
 Resource partitioning
 Reduce niche overlap
 Use shared resources at different
• Times
• Places
• Ways
Competing Species Can Evolve to
Reduce Niche Overlap
Sharing the Wealth: Resource
Partitioning
Specialist Species of Honeycreepers
5-3 What Limits the Growth of
Populations?
 Concept 5-3 No population can continue to
grow indefinitely because of limitations on
resources and because of competition among
species for those resources.
Populations Have Certain
Characteristics (1)
 Populations differ in
• Distribution
• Numbers
• Age structure
 Population dynamics
Populations Have Certain
Characteristics (2)
 Changes in population characteristics due to:
• Temperature
• Presence of disease organisms or harmful
chemicals
• Resource availability
• Arrival or disappearance of competing species
Most Populations Live Together in
Clumps or Patches (1)
 Population distribution
• Clumping
• Uniform dispersion
• Random dispersion
Most Populations Live Together in
Clumps or Patches (2)
 Why clumping?
• Species tend to cluster where resources are
available
• Groups have a better chance of finding clumped
resources
• Protects some animals from predators
• Packs allow some to get prey
• Temporary groups for mating and caring for
young
Populations Can Grow, Shrink, or
Remain Stable (1)
 Population size governed by
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Births
Deaths
Immigration
Emigration
 Population change =
(births + immigration) – (deaths + emigration)
Populations Can Grow, Shrink, or
Remain Stable (2)
 Age structure
• Pre-reproductive age
• Reproductive age
• Post-reproductive age
No Population Can Grow Indefinitely:
J-Curves and S-Curves (1)
 Biotic potential
• Low
• High
 Intrinsic rate of increase (r)
 Individuals in populations with high r
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Reproduce early in life
Have short generation times
Can reproduce many times
Have many offspring each time they reproduce
No Population Can Grow Indefinitely:
J-Curves and S-Curves (2)
 Size of populations limited by
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Light
Water
Space
Nutrients
Exposure to too many competitors, predators or
infectious diseases
No Population Can Grow Indefinitely:
J-Curves and S-Curves (3)
 Environmental resistance
 Carrying capacity (K)
 Exponential growth
 Logistic growth
Science Focus: Why Are Protected Sea
Otters Making a Slow Comeback?
 Low biotic potential
 Prey for orcas
 Cat parasites
 Thorny-headed worms
 Toxic algae blooms
 PCBs and other toxins
 Oil spills
Population Size of Southern Sea Otters
Off the Coast of So. California (U.S.)
No Population Can Continue to Increase
in Size Indefinitely
Logistic Growth of a Sheep Population
on the island of Tasmania, 1800–1925
When a Population Exceeds Its Habitat’s
Carrying Capacity, Its Population Can Crash
 Carrying capacity: not fixed
 Reproductive time lag may lead to overshoot
• Dieback (crash)
 Damage may reduce area’s carrying capacity
Exponential Growth, Overshoot, and
Population Crash of a Reindeer
Species Have Different Reproductive
Patterns
 r-Selected species, opportunists
 K-selected species, competitors
Positions of r- and K-Selected Species on
the S-Shaped Population Growth Curve
Genetic Diversity Can Affect the Size
of Small Populations
 Founder effect
 Demographic bottleneck
 Genetic drift
 Inbreeding
 Minimum viable population size
Under Some Circumstances Population
Density Affects Population Size
 Density-dependent population controls
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Predation
Parasitism
Infectious disease
Competition for resources
Several Different Types of Population
Change Occur in Nature
 Stable
 Irruptive
 Cyclic fluctuations, boom-and-bust cycles
• Top-down population regulation
• Bottom-up population regulation
 Irregular
Population Cycles for the Snowshoe
Hare and Canada Lynx
Humans Are Not Exempt from Nature’s
Population Controls
 Ireland
• Potato crop in 1845
 Bubonic plague
• Fourteenth century
 AIDS
• Global epidemic
Case Study: Exploding White-Tailed Deer
Population in the U.S.
 1900: deer habitat destruction and uncontrolled
hunting
 1920s–1930s: laws to protect the deer
 Current population explosion for deer
• Lyme disease
• Deer-vehicle accidents
• Eating garden plants and shrubs
 Ways to control the deer population
5-4 How Do Communities and Ecosystems
Respond to Changing Environmental
Conditions?
 Concept 5-4 The structure and species
composition of communities and ecosystems
change in response to changing environmental
conditions through a process called ecological
succession.
Communities and Ecosystems Change
over Time: Ecological Succession
 Natural ecological restoration
• Primary succession
• Secondary succession
Some Ecosystems Start from Scratch:
Primary Succession
 No soil in a terrestrial system
 No bottom sediment in an aquatic system
 Early successional plant species, pioneer
 Midsuccessional plant species
 Late successional plant species
Primary Ecological Succession
Some Ecosystems Do Not Have to Start
from Scratch: Secondary Succession (1)
 Some soil remains in a terrestrial system
 Some bottom sediment remains in an aquatic
system
 Ecosystem has been
• Disturbed
• Removed
• Destroyed
Natural Ecological Restoration of
Disturbed Land
Some Ecosystems Do Not Have to Start
from Scratch: Secondary Succession (2)
 Primary and secondary succession
• Tend to increase biodiversity
• Increase species richness and interactions
among species
 Primary and secondary succession can be
interrupted by
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Fires
Hurricanes
Clear-cutting of forests
Plowing of grasslands
Invasion by nonnative species
Science Focus: How Do Species Replace
One Another in Ecological Succession?
 Facilitation
 Inhibition
 Tolerance
Succession Doesn’t Follow a
Predictable Path
 Traditional view
• Balance of nature and a climax community
 Current view
• Ever-changing mosaic of patches of vegetation
• Mature late-successional ecosystems
• State of continual disturbance and change
Living Systems Are Sustained through
Constant Change
 Inertia, persistence
• Ability of a living system to survive moderate
disturbances
 Resilience
• Ability of a living system to be restored through
secondary succession after a moderate
disturbance
 Tipping point
The Human Population and Its Impact
Chapter 6
Core Case Study: Are There Too
Many of Us? (1)
 Estimated 2.4 billion more people by 2050
 Are there too many people already?
 Will technological advances overcome
environmental resistance that populations face?
 Should populations be controlled?
Core Case Study: Are There Too
Many of Us? (2)
 Will growing populations cause increased
environmental stresses?
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Infectious diseases
Biodiversity losses
Water shortages
Traffic congestion
Pollution of the seas
Climate change
Crowded Street in China
6-1 How Many People Can the Earth
Support?
 Concept 6-1 We do not know how long we can
continue increasing the earth’s carrying
capacity for humans without seriously degrading
the life-support system for humans and many
other species.
Human Population Growth Continues but
It Is Unevenly Distributed (1)
 Reasons for human population increase
• Movement into new habitats and climate zones
• Early and modern agriculture methods
• Control of infectious diseases through
• Sanitation systems
• Antibiotics
• Vaccines
Human Population Growth Continues but
It Is Unevenly Distributed (2)
 Population growth in developing countries is
increasing 15 times faster than developed
countries
 By 2050, 97% of growth will be in developing
countries
 Should the optimum sustainable population be
based on cultural carrying capacity?
Global Connections: UN World
Population Projections by 2050
Science Focus: How Long Can the
Human Population Keep Growing?
 Thomas Malthus and population growth: 1798
 Humans have altered 83% of the earth’s land
surface
 Can the human population grow indefinitely?
Natural Capital Degradation: Altering
Nature to Meet Our Needs
6-2 What Factors Influence the Size of the
Human Population?
 Concept 6-2A Population size increases
because of births and immigration and
decreases through deaths and emigration.
 Concept 6-2B The average number of children
born to women in a population (total fertility rate)
is the key factor that determines population size.
The Human Population Can Grow,
Decline, or Remain Fairly Stable
 Population change
• Births: fertility
• Deaths: mortality
• Migration
 Population change =
(births + immigration) – (deaths + emigration)
 Crude birth rate
 Crude death rate
Global Connections: The World’s 10
Most Populous Countries in 2008
Women Having Fewer Babies but Not Few
Enough to Stabilize the World’s Population
 Fertility rate
• Replacement-level fertility rate
• Total fertility rate (TFR)
Case Study: The U.S. Population Is
Growing Rapidly
 Drop in TFR in U.S.
• Rate of population growth has slowed
 Population still growing and not leveling off
• Fourfold increase since 1900
 Changes in lifestyle in the U.S. during the 20th
century
TFR Rates for the U.S. between 1917
and 2008
Birth Rates in the U.S. from 1910 to 2008
Some Major Changes That Took Place in
the U.S. between 1900 and 2000
Several Factors Affect Birth Rates and
Fertility Rates (1)
 Children as part of the labor force
 Cost of raising and educating children
 Availability of private and public pension
 Urbanization
 Educational and employment opportunities for
women
Several Factors Affect Birth Rates and
Fertility Rates (2)
 Infant mortality rate
 Average age of a woman at birth of first child
 Availability of legal abortions
 Availability of reliable birth control methods
 Religious beliefs, traditions, and cultural norms
Several Factors Affect Death Rates (1)
 Life expectancy
 Infant mortality rate
 Why are people living longer and fewer infants
dying?
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Increased food supply and distribution
Better nutrition
Medical advances
Improved sanitation
Several Factors Affect Death Rates (2)
 U.S. infant mortality rate high due to
• Inadequate health care for poor women during
pregnancy and their infants
• Drug addiction among pregnant women
• High birth rate among teenagers
Migration Affects an Area’s Population
Size
 Economic improvement
 Religious freedom
 Political freedom
 Wars
 Environmental refugees
Case Study: The United States: A Nation
of Immigrants
 Historical role of immigration in the U.S.
 Legal immigration
 Illegal immigration
Legal Immigration to the U.S. between
1820 and 2003
6-3 How Does a Population’s Age
Structure Affect Its Growth or Decline?
 Concept 6-3 The numbers of males and
females in young, middle, and older age groups
determine how fast a population grows or
declines.
Populations Made Up Mostly of Young
People Can Grow Rapidly
 Age structure categories
• Prereproductive ages
• Reproductive ages
• Postreproductive ages
Generalized Population Age Structure
Diagrams
Population Structure by Age and Sex in
Developing and Developed Countries
Fig. 6-9a, p. 131
Fig. 6-9b, p. 131
We Can Use Age-Structure Information to
Make Population and Economic Projections
 Baby boomers
 Job market when they retire
Tracking the Baby-Boom Generation in
the United States
Populations Made Up of Mostly Older
People Can Decline Rapidly
 Slow decline
• Manageable
 Rapid decline
• Severe economic problems
• Severe social problems
Some Problems with Rapid Population
Decline
Some Problems with Rapid
Population Decline
Can threaten economic growth
Labor shortages
Less government revenues with fewer
workers
Less entrepreneurship and new business
formation
Less likelihood for new technology
development
Increasing public deficits to fund higher
pension and health-care costs
Pensions may be cut and retirement age
increased
Fig. 6-11, p. 133
Populations Can Decline from a Rising
Death Rate: The AIDS Tragedy
 25 million killed by 2008
 Many young adults die: loss of most productive
workers
 Sharp drop in life expectancy
 International community called upon to
• Reduce the spread of HIV through education and
health care
• Financial assistance and volunteers
6-4 How Can We Slow Human Population
Growth?
 Concept 6-4 Experience indicates that the most
effective ways to slow human population growth
are to encourage family planning, to reduce
poverty, and to elevate the status of women.
As Countries Develop, Their Populations
Tend to Grow More Slowly
 Demographic transition stages
• Preindustrial
• Transitional
• May lead to a demographic trap
• Industrial
• Postindustrial
Four Stages of the Demographic
Transition
Planning for Babies Works
 Family Planning
• Responsible for a 55% drop in TFRs
• In developing countries
• Expansion of program
• Include teenagers, sexually active unmarried
women, and men
 Slow and stabilize population growth
• Invest in family planning
• Reduce poverty
• Elevate the social and economic status of women
Empowering Women Can Slow
Population Growth
 Education
 Paying jobs
 Human rights without suppression
 “For poor women the only holiday is when you
are asleep”
Women from a Village in Burkina Faso
Returning with Fuelwood
Case Study: Slowing Population Growth
in China: the One-Child Policy
 Encourages fewer children
 Gender imbalance
 Fast-growing economy
 Face serious resource and environmental
problems
Case Study: Slowing Population
Growth in India
 Population control: gender bias
 Poverty
 Malnutrition
 Environmental problems