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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.