1. Understanding Populations
How Populations Change in Size

2. What is A Population? Members of a species that live in the same place
They can breed with each other

3. Populations

4. The term population can refer to:
A group in
general
The size of the population
= number of
individuals

5. Properties Of A Population
Size:
how large it is
Ex. 50 deer, deer
Density:
how many individuals are in one area
Ex. Deer in a certain forest

6. Properties Of A Population
Distribution: how spread out the organisms are
even: equally spread out
clumped: hanging around in groups
random: spread out any old way

8. How Does a Population Grow?
A population will grow if there are more births than deaths.
Change in Population Size = Births – Deaths

9. How Does a Population Grow?
Growth rate is an expression of the increase in the size of an organism or population over a given period of time. It is the birth rate minus the death rate.
Overtime, the growth rates of populations change because birth rates and death rates increase or decrease.
For this reason, growth rates can be positive, negative, or zero.
Growth Rate= Birth Rate – Death Rate .

10. How Does a Population Grow?
For the growth rate to be zero, the average number of births must equal the average number of deaths.
A population would remain the same size if each pair of adults produced exactly two offspring, and each of those offspring survived to reproduce.
If the adults in a population
are not replaced by new
births, the growth rate will
be negative and the
population will shrink.

11. How Fast Can a Population Grow?
Populations usually stay about the same size from year to year because various factors kill many individuals before they can reproduce.
These factors control the sizes of populations.
In the long run, the factors also determine how the population evolves.

12. How Fast Can a Population Grow?
Biotic potential – fastest rate an organism can grow
Depends on the reproductive potential – number of individuals that a species can produce.
Ex. Bacteria breed faster than humans.

13. Populations may sometimes undergo exponential growth – grow faster and faster.
occurs in nature only when populations have plenty of food and space, and have no competition or predators

14. Exponential Growth Curve14

15. What Limits Population Growth?
Carrying Capacity: ability of an ecosystem to support the maximum size of a population.
Ex. How many cows can your pasture feed?
Ex. How many tomato plants can you plant in your garden?

16. Carrying Capacity

17. What Limits Population Growth?
Resource Limits: available food and land size
Limited resources determine the carrying capacity for that species in that environment
Ex. rabbits in Australia

18. Animal Plant – Australian Rabbits

19. What Limits Population Growth?
Competition Within a Population:
For food
For territory
land
water
space

20. http://www. animalplanet

21. Two Types of Population Regulation: affects the population
Density Dependent: Depends on the population size.
Ex. If there are too many organisms there will be a shortage of food and space.

22. Loblolly Pines infected with Southern Pine Beetle

23. Density Dependent Ex. Great Britain

24. Density Independent: Does not depend on the population size.
Ex. Floods, fire, earthquakes, hurricanes, tornados