Chapter 5 and 6- Chapter 5 and 6- Populations Prentice Populations Prentice

HallHallpgs. 118-132pgs. 118-132

Biology I 2004-2005Biology I 2004-2005

What Affects Population Size?What Affects Population Size?

A population is a group of organisms belonging to a single species that lives in a given area. A population is a group of organisms belonging to a single species that lives in a given area.

Imagine that each of the three different colors of paper clips that you have in an envelope Imagine that each of the three different colors of paper clips that you have in an envelope represents a different species of organisms. represents a different species of organisms.

Working with a partner and using the envelopes of paper clips that you both have, answer Working with a partner and using the envelopes of paper clips that you both have, answer the following questions.the following questions.

1.1. How many populations of organisms do you have in your envelope? In your partner’s How many populations of organisms do you have in your envelope? In your partner’s envelope?envelope?

2.2. Choose one of the populations in one of the envelopes. How might this population grow in Choose one of the populations in one of the envelopes. How might this population grow in size?size?

3.3. How might this same population decrease in size?How might this same population decrease in size?

1.1. How many populations of organisms do you have in How many populations of organisms do you have in your envelope? In your partner’s envelope?your envelope? In your partner’s envelope?

Each envelope represents a community of organisms, Each envelope represents a community of organisms, and each color of paper clip in each envelope represents a and each color of paper clip in each envelope represents a

single population. Therefore, each student should have three single population. Therefore, each student should have three populations represented.populations represented.

2.2. Choose one of the populations in one of the envelopes. Choose one of the populations in one of the envelopes. How might this population grow in size?How might this population grow in size?

The population (some paper clips) could reproduce, or The population (some paper clips) could reproduce, or some could move from the partner’s envelope into the other some could move from the partner’s envelope into the other

envelope (immigration).envelope (immigration).

3.3. How might this same population decrease in size?How might this same population decrease in size?

The population (some paper clips) could be thrown The population (some paper clips) could be thrown away (death), or away (death), or

some could move from the partner’s envelope into the other some could move from the partner’s envelope into the other envelope (emigration).envelope (emigration).

Chapter 5 Outline5–1 How Populations Grow

A.     Characteristics of PopulationsB.      Population GrowthC.      Exponential GrowthD.      Logistic Growth

5–2 Limits to GrowthA.     Limiting FactorsB.      Density-Dependent Factors

1. Competition2. Predation3. Parasitism and Disease

C.  Density-Independent Factors5–3 Human Population Growth

A.     Historical OverviewB.      Patterns of Population Growth

1. The Demographic Transition2. Age Structure

C. Future Population Growth

5–1 How Populations GrowA. Characteristics of Populations

B. Population GrowthC. Exponential Growth

D. Logistic Growth

Characteristics of a Population

1- Geographical Distribution

2- Density

3- Growth Rate

1- Geographical Distribution

-area inhabited by a population

-could be as small as a few cubic centimeters like a bacteria or as large as millions of kilometers like killer whales

2- Population Density the number of individuals per unit How organisms are dispersed can be important Three patterns of dispersal are random, clumped, and

uniform

3- Growth Rate- 3 factors that affect a populations size

- number of births- number of deaths- number of individuals entering and leaving a population

A population will increase or decrease in size depending on the number added or removed from it

A population will grow if: Birth Rate > Death Rate(# of individuals born) (# of individuals who die)

A population will stay the same if: Birth Rate = Death Rate

A population will decline if: Birth Rate < Death Rate

Individuals entering and leaving the population will also increase or decrease a population’s sizeImmigration- movement of individuals into an area (increase population)Emigration- movement of individuals out of an area (decrease

population)

Population Growth

1

2

3

4

5

1. Initial growth- birth (natality) is high2. Exponential growth3. Carrying capacity- steady state4. Decline- increase in death rate5. Extinction

In 20 minutes the population is 2In 40 minutes the population is 4In 1 hour: the population is 8In 2 hours: 64In 3 hours: 512In one day: 4,720,000,000,000,000,000,000

Exponential Growth If a population has abundant space and food, protection from

predators and disease then the organisms in the population will multiply and the population will increase

Under ideal conditions with plenty of nutrients, heat, moisture, & light a bacteria can reproduce by splitting in half within 20 minutes producing 2 bacteria

The pattern of growth is a J-shaped curve and the population is undergoing exponential growth

Exponential growth occurs when the individuals in a population reproduce at a constant rate

1 million

500,000

100One year

Pop

ula

tion

siz

e

At first, the number of individuals increases slowly, over time the population becomes larger and larger until it approaches an infinitely large size

Under ideal conditions with unlimited resources, a population will grow exponentially

Logistic Growth Exponential growth doesn’t continue in natural populations for

very long If a new species of organism is introduced into a new

environment, at first the population grows slowly, then exponentially, eventually the population growth slows down (the size has not dropped, but the population is growing slower)

As resources become less available, the growth of a population slows or stops forming an S-shaped curve- logistic growth

Logistic Growth occurs when a population’s growth slows or stops following a period of exponential growth

Birth rate decreases and death rate increases

Carrying Capacity

When growth levels off The population is not

growing Carrying capacity- the

largest number of individuals that an environment can support

When a population overshoots the carrying capacity, then limiting factors may come into effect

A balance between environmental factors must exist for a population to survive

For example: Producers = consumers Water use = Rainfall

PopulationGrowth

can be

represented bycharacterized by characterized by represented by

which cause a

Exponentialgrowth

Logisticgrowth

Fallinggrowth rate

S-shapedcurve

Limits ongrowth

No limits on growth

J-shapedcurve

Constantgrowth rate

Unlimitedresources

What can limit growth?5–2 Limits to Growth

A. Limiting Factors

B. Density-Dependent Factors

1. Competition

2. Predation

3. Parasitism and Disease

C. Density-Independent Factors

Limiting Factors Any factor that causes

population growth to decrease

Limiting factors, such as availability of food, disease, predators, or lack of space, will cause population growth to slow

Under these pressures, the population may stabilize in an S-shaped growth curve

J curve S curve

Carrying capacity

Exponential growth

Time

Pop

ula

tion

DIS

EA

SE

SPA

CE

PR

ED

A-

TO

RS

FO

OD

0

Characteristics of Population Growth

Density-Dependent Limiting Factors

A limiting factor that depends on population size is a Density-dependent limiting factor

Density-dependent factors include disease, competition, predators, parasites, and food.

Disease, for example, can spread more quickly in a population with members that live close together.

Density dependent factors create an S-shaped curve

Organism Interactions Limit Population Size

Population sizes are limited not only by abiotic factors, but also are controlled by various interactions among organisms that share a community.

Predation affects population size

Predation is a density-dependent factor

When a predator consumes prey on a large enough scale, it can have a drastic effect on the size of the prey population

Populations of predators and their prey are known to experience cycles or changes in their numbers over periods of time

Competition within a population Competition is a density-dependent factor

When only a few individuals compete for resources, no problem arises

When a population increases to the point at which demand for resources exceeds the supply, the population size decreases

Competition can also occur between members of different species- this creates evolutionary change

The two species competing are under stress to change in way that decrease competition- eventually evolving to occupy separate niches

Predation affects population size

The data in this graph reflect the number of hare and lynx pelts sold to the Hudson’s Bay Company in northern Canada from 1845 through 1935.

Lynx and Hare Pets Sold to the Hudson’s Bay Company

Num

ber

of o

rgan

ism

s in

tho

usan

ds)

Times (in years)

LynxHare

Moose Wolves

• The periodic increase in the moose population is quickly followed by a rise in the number of wolves.

• This increase in the number of wolves increases the number of moose captured by their predator and the moose population drops.

• The wolf population will then decrease after the moose numbers drop because the wolves are less able to find food.

• The predator prey cycle can be repeated indefinitely.

Parasitism and Disease Parasites can also limit a population’s

size-density-dependent As the # of individuals , parasites

which then causes the # of individuals to Parasites are similar to a predator in

that they take nourishment at the expense of their host

As a population increases in size, disease is more common because individuals are in closer contact with one another

Density-independent limiting factors and population growth

Density-independent factors can affect all populations, regardless of their size

Most density-independent factors are abiotic factors, such as temperature, storms, floods, drought, and major habitat disruption

Density-Independent FactorsDensity-Independent Factors Density-independent factors

create a boom-and bust curve (exponential growth followed by a sudden collapse)

Examples: Weather- a drought kills

grass Human activity:

deforestation- destroys habitat

Seasons: a severe winter regulates insect population

Boom-and-Bust Curve

Time

Population

Density

Limitations on Population Growth

Reproduction Patterns

In nature, animal and plant populations change in size.

Biologists study the factor that determines population growth—an organism’s reproductive pattern, also called its life-history pattern

A variety of population growth patterns are possible in nature- R strategists and K-strategists

Rapid life-history patterns- R Strategists

rapid life-history patterns are common among organisms from changeable or unpredictable environments

rapid life-history organisms have a small body size, mature rapidly, reproduce early, and have a short life span

Slow life-history patterns – K-strategists large species that live in more stable environments large species that live in more stable environments

usually have slow life-history patterns.usually have slow life-history patterns.

reproduce and mature slowly, and are long-lived. They reproduce and mature slowly, and are long-lived. They maintain population sizes at or near carrying capacitymaintain population sizes at or near carrying capacity

Demography Demography, the study of human population size,

density and distribution, movement, and its birth and death rates

Demography examines the characteristics of human populations and attempts to explain how those populations will change over time

Demographic transition- a change in a population from high birth and death rates to low birth and death rates; Examples- United States and Japan

5–3 Human Population Growth A. Historical Overview B. Patterns of Population Growth 1. The Demographic Transition 2. Age Structure C. Future Population Growth

Agriculturebegins

Plowingand irrigation

Bubonicplague

IndustrialRevolutionbegins

Human Population Growth

Agriculture

begins

Plowing and irrigation

Bubonic plague

Industrial Revolution Begins

Until about 500 years ago, the population grew slowly. Agriculture and industry made life easier and safer.

Human Population

We are growing exponentially Due to technological advances: medicines, a dependable

food supply, and sanitation The death rate is decreasing and the life expectancy is

increasing The human population will eventually reach its carrying

capacity

Population Distribution Per Age Range for Several CountriesA

ge

Stable growth Rapid growth Slow growth

Male

Female

Reproductive years

Population (percent of total for each country)

Age StructureAge Structure

Population growth depends on how many people of different ages make up a given population

Demographers can predict future growth using age-structure diagrams Age-structure diagrams graph the number of people in each age group

U.S. Population Rwandan Population

Age Structure

Ch.6-2: Human Impact on the Environment

Air Greenhouse effect

• Trapping of heat by gases in the Earth’s atmosphere (carbon dioxide)

• This may lead to global warming- increase in the Earth’s temperature from the rapid buildup of carbon dioxide and other greenhouse gases

Acid Rain

• Burning of fossil fuels release nitrogen and sulfur into the atmosphere which combined with water form nitric and sulfuric acid

• Acid Rain kills plants Smog

• Mix of chemicals in the air from automobile exhaust

• Affects the respiratory system especially those with asthma

Emissions to AtmosphereNitrogen oxidesSulfur dioxide

Chemical TransformationNitric acid

Sulfuric acid

PrecipitationAcid rain, fog,snow, and mist

Dry Fallout

Condensation

particulates, gases

Industry Transportation Ore smelting Power generation

Section 6-2 The Formation of Acid Rain

Human Impact of the Environment

Water Excessive nutrients can cause an increase in algae

growth and depletion of oxygen for other organisms Over harvesting of fish has reduced the number of

fish

Human Impact of the Environment

Land Erosion

• The wearing away of surface soil by water and wind

Desertification• The combination of farming, overgrazing, and

drought in dry climates which turn productive areas into deserts

Deforestation• The loss of forests which leading to severe erosion

and changes in soil properties

Deforestation erosion water pollution and desertification

Consequences If humans continue to alter the environment, they will

have to deal with the results Examples: fossil fuels combustion, habitat

destruction, deforestation, ozone layer destruction, global warming

Human Overpopulation results in: Worldwide malnutrition Increased disease Increased pollution

Humans need to learn to be a part of nature not apart from nature!

Ch. 6-3: Biological Diversity Ecosystem diversity- variety of

habitats, communities, and ecological processes in the living world

Species diversity- the number of different species

Genetic diversity- sum total of all the different forms of genetic information carried by all organisms living on Earth today

Biodiversity increases as you move toward the equator.

Areas around the world differ in biodiversity

Biodiversity can bring stability to an ecosystem.

Biodiversity is one of the world’s greatest resources

Variations within a species also helps protect against disease or parasite

Genetically different individuals within a species have a better chance of resisting disease

Example: world cheetah population reduced by a single virus

Tree plantation has same type of trees (single species) vulnerable to disease, etc..- spread easily

Diversity among individuals in a population is important to resistance of population as a whole (genetically different)

Biological diversity causes ecological stability

Adaptations- changes in response to factors in the environment (physical and behavioral changes)

Slow process that takes place over many generations Organisms can be specialized to occupy a specific niche Advantages

The more specialized an organism’s method of obtaining food and life requirements are (NICHE), the less competition they will have with other species (they have a better chance of surviving)

Example: anteater with long snout can reach into ant hills

Disadvantages If there are changes in the environment, organisms may

not be able to adapt fast enough in response Example: Koala bears eat only Eucalyptus trees

Insects

BacteriaFungi

Plants

Protists Other Animals

54.4%

4.2%

18%

3.4%0.3%

19.7%

Species Diversity

Loss of Biodiversity Extinction is the

disappearance of a species when the last of its members dies

Extinction is a natural process and Earth has experienced several mass extinctions during its history

A species is considered to be an endangered species when its numbers become so low that extinction is possible

Threats to Biodiversity Complex interactions among species make each ecosystem

unique Changes to habitats can therefore threaten organisms with

extinction Human activity can reduce biodiversity by altering habitats,

hunting species to extinction, introducing toxic substances into food webs, and introducing invasive species

Habitat loss-One of the biggest reasons for decline in biodiversity

Threats to Biodiversity: Habitat fragmentation

Habitat fragmentation is the separation of

wilderness areas from other wilderness

areas

Habitat fragmentation creates “islands” of

habitat that are isolated from each

other

Threats to Biodiversity: Demand for wildlife products

Hunting has caused many animals to go extinct

For example: passenger pigeon and Stellar sea cow

Humans hunt for food, fur, hides, and body parts thought to have medicinal properties

In the United States animals are protected from hunting if they are endangered

Threats to Biodiversity: Biological Magnification

Increasing concentrations of a harmful substance in organisms at higher trophic levels in a food chain or web

Example: DDT

Water

Producers

Zooplankton

Small Fish

LargeFish

Fish-Eating Birds

Magnification ofDDT Concentration

1000

10,000

100,000

1,000,000

10,000,000

1

Threats to Biodiversity: Introduced Species

Introduced species threaten biodiversity

Introduced species are organisms that have been introduced into new habitats and often become invasive, reproduce rapidly

Invasive species lack density-dependent limiting factors to keep their populations in check and take over areas and out compete existing species

Native to South America, nutrias have become pests in coastal areas of se US. These furry rodents eat water plants that protect fragile shorelines from erosion. This destroys the habitats of species native to those ecosystems.