Transcript Populations - Cloudfront.net

Chapter 5
Populations
Group of individuals that belong to the same
species and live in the same area
California Biology Science Standards
B1 6.b. Students know how to analyze changes in an ecosystem from
changes in climate, human activity, introduction of nonnative species, or
changes in populations size.
B1 6.c. Students know how fluctuations in population size in an ecosystem
are determined by the relative rates of birth, immigration, emigration, and
death.
Characteristics of Populations
1. Geographic distribution:
- area inhabited by a population
- can range in size and shape
2. Population Density:
- the # of individuals per unit area
- # can vary
3. Population Growth:
- how a population grows or decreases
in size
Factors that affect population size
1.
2.
3.
# of births
# of deaths
# of individuals that enter or leave a
population
Scenarios:
If population grows?
If population decrease?
If population stays the same?
Immigration

Movement of individuals into a population

Cause population to increase in size
Emmigration

Movement of individuals out of a
population

Causes population to decrease in size
Population Growth Concept Map
Section 5-1
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
Go to
Section:
represented by
S-shaped
curve
Exponential Growth
- Occurs when the individuals in a population
reproduce at a constant rate
- in the beginning #’s increase slowly
- over time the pop. becomes so large it is
exponential (VERY BIG !!!!!!!!)
- Only can happen when the pop. has:
1. abundant space & food
2. protection from predators & disease
3. the ability to reproduce
*** does not continue for a long time***
Examples of Exponential Growth
Find graphs on internet
Logistic Growth
-
Occurs when a populations growth slows
or stops following a period of exponential
growth
Caused by:
1. resources become less available
2. birthrate ↓ deaths ↑ or they are equal
3. immigration ↓ emmigration ↑ or
they are equal
-
Figure 5-4 Logistic Growth of Yeast
Population
Section 5-1
Carrying Capacity
• The largest # of individual that a given
environment can support
Carrying capacity
Time (hours)
Go to
Section:
Limits to Growth

Limiting Factor:
- a factor that causes population growth to
decrease
- can be Density Dependent or
Density Independent
Density – Dependent Factors
Limiting factors that depend on population
size
 Become limiting only when the population
density (# of individuals) reach a certain
level
 Affect very large populations only

Types of Density Dependent Factors
1. Competition – when populations become
crowded, they start to compete for: food,
water, space & sunlight
- can be among the same species or different
species
2. Predation – often controls populations in
nature ** predator/prey relationships**
3. Parasitism & Disease – take nourishment
from the host causing death or disease.
Density-Independent Factors
Affect all populations regardless of size
 Types:
1. unusual weather
2. natural disasters
3. seasonal cycles
4. human activities

How populations respond to the factors


Populations size crashes
But most will build up again or may stay
low for some time
Always Remember….
1. Environments are always changing
2. Most populations can adapt to the changes
3. Population will grow & shrink in response
4. Major upsets can lead to long term decline
(usually caused by human activity)
Human Population Growth






Like other organisms, human population tends to
increase with time
For most of human existence – population has grown
slowly (limited food source/incurable disease)
About 500 years ago – population began growing
more rapidly
Causes: agriculture & industry (easier & safer)
food supply more reliable
goods shipped around the world
improved sanitation
Result: decreased death rate & birthrate increase
So….. Humans experienced EXPONENTIAL GROWTH
Human Population Growth
Section 5-3
Industrial
Revolution
begins
Agriculture
begins
Plowing
and
irrigation
Go to
Section:
Bubonic
plague