#### Transcript Populations - Cloudfront.net

```Chapter 5 and 6Populations
Biology I
What Affects Population Size?
A population
is a group of
organisms belonging to a single
species that lives in a given area.
Populations
size is affected by
# of births, # of deaths, & # of
individuals who enter or leave
5–1 How Populations Grow
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:
A population will decline if:
Birth Rate = Death Rate
Birth Rate < Death Rate
Population Growth
3
2
1
1.
2.
3.
4.
5.
4
5
Initial growth- birth (natality) is high
Exponential growth
Carrying capacity- steady state
Decline- increase in death rate
Extinction
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
In 20 minutes the population is 2
In 40 minutes the population is 4
In 1 hour: the population is 8
In 2 hours: 64
In 3 hours: 512
In one day: 4,720,000,000,000,000,000,000


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
At first, the number of individuals increases slowly, over time
the population becomes larger and larger until it
approaches an infinitely large size
Population size
1 million
500,000
100

One year
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
Population
Growth
can be
Logistic
growth
Exponential
growth
characterized by
No limits on
growth
Unlimited
resources
represented by
Constant
growth rate
J-shaped
curve
characterized by
Limits on
growth
which cause a
Falling
growth rate
represented by
S-shaped
curve
5–2 Limits to Growth What can limit growth?



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
Population
Carrying
capacity
0
J curve
S curve
Time
FOOD
PREDATORS
SPACE
Exponential
growth
DISEASE
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, and parasites.

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
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
 Parasites are similar to a predator in
that they take nourishment at the
expense of their host

Density-independent limiting factors
and population growth
 Density-independent
factors can affect all
populations,
regardless of their
size
 Most
densityindependent factors
are abiotic factors,
such as temperature,
storms, floods,
drought, and major
habitat disruption
Density-Independent Factors

Density-independent
factors create a population
crash
(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
Population Growth after a Density_____________ Limiting Factor
Population
Density
Time
Limitations on Population Growth
Reproduction Patterns
 In
nature, animal and plant
populations change in size.
 Biologists
that study the factor that
determines population growth—
Demographers

5–3 Human Population Growth
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
Human Population Growth
Industrial
Revolution
IndustrialBegins
Agriculture
begins
Agriculture
begins
Revolution
begins
Bubonic
Plowing
and
Plowing
irrigation
and
plague
Bubonic
plague
irrigation
Until about 500 years ago, the population grew slowly.
Agriculture, industry, & sanitation 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
Age Structure
Population Distribution Per Age Range for Several Countries
Stable growth
Rapid growth
Male
Slow growth
Reproductive years
Age
Female
Population (percent of total for each country)



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
Age Structure
U.S. Population
Rwandan Population
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
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
Consequences

If humans continue to alter the environment, they will
have to deal with the results
 Examples: deforestation, ozone layer destruction,
global warming
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)
Species Diversity
Insects
54.4%
Protists
4.2%
Other Animals
19.7%
Plants
18%
Fungi Bacteria
0.3%
3.4%
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
 Humans hunt for food, fur, hides, and body
parts
 In the United States animals are protected
from hunting if they are endangered
Fish-Eating Birds
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
Magnification of
DDT Concentration
10,000,000
Large
Fish
1,000,000
Small Fish
100,000
Zooplankton 10,000
Producers
Water
1000
1
Threats to Biodiversity: Invasive Species

Invasive species threaten
biodiversity
 Invasive species are organisms that
have been introduced into new
habitats and often become invasive,
reproduce rapidly
 Invasive species lack densitydependent 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.
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