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 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 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 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 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 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? 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 20 th 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? 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

Fig. 6-11, p. 133 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

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