1. ENERGY TRANSFER
Populations

2. What is a Population?
A group of the same species of organism living in the same place

3. Characteristics of Populations
4 Major Characteristics of Populations:
Geographic Distribution
Density
Growth Rate
Age Structure

4. #1 - Geographic Distribution
Describes the area in which a certain population lives
Varies greatly in size depending on the type of organism and population size

5. #2 - Population Density The Number of Organisms Per Unit Area/Volume
Measures the “crowdedness” of a population
Some population densities
for human populations 

6. #3 - Population Growth Rate
The Amount by which a Population Size Changes in an Given Time Period
Depends on:
A) # of Births (birthrate)
B) # of Deaths (death rate)
C) # of Organisms entering or leaving population
Immigration Emigration

7. #3 - Population Growth Rate
Exponential Growth Model
Indefinite Growth of a population due to unlimited resources (food, shelter,etc) and a lack of limiting factors (predators, disease, competition, and other factors that decrease population growth).
Forms a J-Shaped Curve!
This does not happen except
in rare conditions for short
periods of time (like Bacteria in
a culture).

8. More on Exponential Growth…
When a population has unlimited resources, and it continues to grow to its FULL LIVING POTENTIAL, it is called Biotic Potential.
A population that has reached biotic potential has reached its maximum reproductive capacity (i.e. it has reproduced as much as it possibly can)

9. #3 - Population Growth Rate
Logistic Growth Model
More realistic; accounts for Limiting Factors
Begins with exponential growth but slows down or stops as limiting factors influence the population
Populations reach a Carrying Capacity (K), the # of individuals the environment can support over a long period of time.
Forms an S-Shaped Curve!
Region A= very close to exponential growth
Region B= declining birthrate; inc. death rate
Region C= pop. reaches K; usually fluctuates
around Carrying Capacity

10. Limiting Factors 2 Types: (1) Density-Dependent Factors
(2) Density-Independent Factors
DENSITY-DEPENDENT FACTORS are those factors that affect a population depending on its size
- these include food, predation, parasitism, and disease
- Competition can be Interspecific or Intraspecific.
- As the population increases, it is more affected by density-dependent factors

11. The Effect of Predation
Populations in nature are often controlled by predation
The regulation of a population by predation takes place within the predator-prey relationship (one of the best known mechanisms of population control)

12. Limiting Factors
DENSITY-INDEPENDENT FACTORS affect all populations similarly regardless of population size.
The majority of these factors are abiotic.
Examples include: natural disasters, rapid climate changes (drought or floods), and human activity and disturbances

13. #4 – Age Structure
Describes how many individuals of different ages make up a population
Populations with large numbers of young offspring have greater potential for rapid growth
Population Pyramids, or Age-Structure, Diagrams, show age structure in a population.

14. Human Population Growth
It took from the beginning of mankind to around 1800 for the human population to reach 1 Billion.
In the last 200 years, the Human Population has reached just over 6 Billion.
The U.N. estimates the world’s population to be 12.5 Billion by 2050.
What effects will these
numbers have on the
Earth? Other forms of
life?

15. Patterns of Population Growth
The scientific study of human populations is called demography
Examines the characteristics of human populations and attempts to explain how those populations will change over time
Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly
Talk about Thomas Malthus…pg 130.

16. The Demographic Transition
Over the past century, population growth in the US, Japan, and much of Europe has slowed dramatically.
One hypothesis as to why these countries have slowed in their growth is the demographic transition (a dramatic change in birth and death rates).
As countries modernize, there are advances in nutrition, medicine, and sanitation.
These result in more children surviving into adulthood and more adults living to old age.
These changes lower the death rate and begin the demographic transition.

17. The Demographic Transition
Figure 5-12 on pg. 130.
Over the past century, population growth in the US, Japan, and much of Europe has slowed dramatically. One hypothesis as to why is that these countries have completed the demographic transition (a dramatic change in birth and death rates).
As countries modernize, advances in nutrition, medicine, and sanitation result in more children surviving into adulthood and more adults living to old age. These changes lower the death rate and begin the demographic transition.
Figure 5-12 explanation of chart.