1. Populations
Biology – Ch 5

2. Population Characteristics
Geographic distribution
Density
Growth rate
Age structure
*Characteristics used to describe any population found in nature*

3. Geographic Distribution
Area where the population is found (“range”)
Geographic distribution is also a function of WHEN.
Tiger population range change over 90 years (click)
Grizzly bear population range

4. Population Density The number of individuals in a unit area
Density is also dependant on WHEN.

5. Growth rate
Populations tend to stay somewhat the same size from year to year.
However, populations may change due to three factors:
Number of births
Number of deaths
Immigration & emigration
Immigration = “in” (individuals entering a population). Emigration = “exit” (individuals exiting/leaving a population)

6. Growth Rate Representations
Unlimited resources and ideal conditions allow a population to grow without limits = exponential growth
(Click for bacterial growth example)

7. Logistic Growth Curve Realistic population growth in nature
Population growth is limited by resources, competition & natural events
The largest number of individuals that a given environment can support = carrying capacity

8. Reality
WHAT kinds of things might cause RESISTANCE to population growth?

9. Limits to Population Growth
Limiting factor = a factor that causes population growth to decrease
Parasitism
Predation
Population SIZE
Competition
Click to watch a bunny love story…
Density Dependent
Disease
Human interaction
Density Independent
Climate extremes

10. Density Dependent Factors
Limiting factors that depends upon population size
Factors that are limiting only when a population reaches a certain size
Don’t affect smaller populations as strongly as larger populations
Biotic: competition, predation, parasitism, disease

11. Density-Independent Factors
Limiting factors that do NOT depend upon population size
Factors that limit population size regardless of how large a population might be
Affects both large and small populations
Abiotic: unusual climate, natural disasters, seasonal cycles, certain human activities (damming rivers, clear-cutting forests)

12. Human Population Growth
Human population growth exhibited the same characteristics as any organism population growth in nature
EXPONENTIAL
Is there a “carrying capacity” for the human population? If so, what is it? Have we reached it? What happens if we do reach this?

13. Human Population Growth Patterns
Demography = the scientific study of human population growth, including:
Birth rates
Death rates
Age structures
(This helps predict world population needs)
A dramatic change in birth and death rates may be caused by a demographic transition in a country.
A dramatic change due to economic/cultural changes

14. WHY does each group shown above exhibit the particular growth rate patterns?

15. Age Structure Diagrams
WHY/HOW does each graph describe each type of growth (rapid, slow, declining)?
Populations described by age groups

16. Just for information – do NOT need to remember

17. Future Population?
How does world population growth affect QUALITY OF LIFE?

18. Epilogue
One of the most obvious characteristics of human evolution and history has been the exponential growth in the world-wide human population. As such exponential population growth continues, it will have a significant impact upon every aspect of human existence from increasing demand on natural resources to the proliferation of mega-cities and the infrastructure needs of an increasingly urbanized world population. Despite having one of the lowest population growth rates of any country, according to the U.S. Census Bureau, the U.S. population is nevertheless projected to growth from the current 300 million to somewhere between 422 to 458 million by the year The United States and most of the developed nations are also likely to experience an increased aging of their populations, with the current 15 percent of the population that is age 65 or older expected to increase to approximately 20 percent by At the same time, however, the United States is expected to experience an even greater surge of young workers as the U.S. population between the ages of 15 to 64 years old is projected to grow by 42 percent. This is in contrast to other countries such as China where the same age group is expected to decline by 10 percent and Europe where the working age population is expected to decline by 25 percent. Japan faces an even more severe problem as the working age population is expected to decline by 40 percent by the year But population is not affected just by growth rates – but is also affected by the migration of people. As a consequence, another factor that is likely to affect the population of countries are such variables as quality of life, cost of living, availability of jobs, and wars that displace people and cause migrations of people.
Just food for thought…..