1. Population Dynamics in Ecosystems
Bio.2.1.4, Bio.2.2.1, Bio.2.2.2

2. Population Dynamics Populations often change size over time.
Some increase in size, others decrease.
We will concentrate on population growth:
How fast?
For how long will growth continue?
Population Density: # of individuals per unit area
Population Growth Around the World since 1 A.D.

3. Population Dynamics Population growth can be exponential: Time
# of Individuals
J-Shaped Curve
Population of Seagulls..

4. EXPLOSION Population Growth
Exponential growth: when the number of organisms grows by a constantly increasing rate.
Ideal situation with unlimited resources.
Results in a population
EXPLOSION

5. Population Dynamics
R-selected: organisms that grow out of control, exponentially
Exponential growth can occur for short periods of time, but cannot continue forever!
Why?
What limits exponential growth?
Mice and weeds are examples of r-selected organisms

6. Population Dynamics Population growth can be logistic:
S-Shaped Curve
Time
# of Individuals
Population of Elephants….
Logistic Growth: a population’s growth slows or stops following a period of exponential growth.

7. Population Dynamics
Carrying Capacity: The number of organisms of one species that a habitat or environment can hold
Once carrying capacity (k) is reached, the population maintains at that size.
These populations of organisms are called
k-selected.
Most primates and Elephants are k-selected

8. Population Dynamics
Time
# of Individuals k
For logistic growth, population sizes always level out at the carrying capacity (k)

9. Characteristics of K and R selected organisms
K-selected organisms:
Big
Usually mammals (parental care)
Longer life span
Stable environments
Humans, bears, elephants
R-selected organisms:
Small bodied
Often insects
Short Life span
Mature early, lots of offspring
Mosquitoes, bacteria.

10. Population Dynamics
Limiting Factors: Biotic or abiotic factors that restrict or prevent the existence, numbers, reproduction, or distribution of organisms.
Ex. A predator such as a lynx is a limiting factor for a prey such as a hare.
Ex. A cold snowy winter is a limiting factor for thousands of species that would die under those conditions.
Ex. In brackish water, fish can’t pass from salt water to fresh water. The salinity of the water is a limiting factor.

11. Population Dynamics Limiting Factors can be biotic or abiotic.
*List examples of each!
Abiotic
Biotic

12. Population Dynamics
Density Dependent Factors: Factors that limit the size of a population and only exist when populations get too big
Ex. Disease, competition, parasites, and a limited amount of food.
These would not have caused so many problems had the population remained small.

13. Population Dynamics
Predation: One animal constantly consuming another, limits its’ population size
Ex. Owls keeping a mouse population small, or hunters keeping deer numbers in check.
Ex: Lynx and Hare
Predator can’t eat all prey or food will be gone for good.

14. Lynx Chases Hare

15. Lynx and Hare Graph

16. Population Dynamics
Competition: A density dependent factor. Individuals competing for limited food source or other resources.
Crowding and Stress: Not completely understood, but causes:
fighting
Infertility
decreased parental care
decreased immunity to disease
death
Parasitism and Disease: parasites limit the growth of a population by causing diseases

17. Population Dynamics
Floods
Density Independent Factors: Limiting factors that would affect all populations regardless of size
Most are abiotic factors.
Ex. Floods, hurricanes, drought, habitat destruction.
Volcanic Eruptions
Fire

18. Human Population Growth
Demography: the study of human population growth characteristics.
Scientists called Demographers.
See Fig on p. 129 for graph of exponential human growth.
Demographic transition: a dramatic change in birth and death rates

19. Human Population Growth
Birth Rate: Usually it’s the number of babies that were born in the past year.
# of births in a sample size of 1000 individuals
Death Rate: Usually it’s the number of people who have died in the past year.
# of deaths in a sample size of 1000 individuals

20. Human Population Growth
Fertility Rate: The number of babies each woman is having during her fertile years.
Total Fertility rates in the U.S. from 1917 to2000.
Note: Baby Boom After WWII

21. Human Population Growth
Age Structure: can be used to determine how quickly a country or area is growing.
Are most individuals post-reproductive?
Are most individuals reproductive?
Are most individuals pre-reproductive?
Which of these would most likely be growing the fastest?
The slowest?
  Populations that are not growing have about the same numbers of each age group.   
See p. Fig 5.13 pg. 131
Age Structure Diagram: population profiles, graphing the number of people in different age groups
Age Structure Diagram

23. Human Population Growth
Immigration: movement by individuals into a country or area.
Emigration: movement by individuals out of a country or area.
Neither change world populations but both change populations of the countries involved.