1. Population Ecology

2. What is population?
Group of individuals of the same species that live in the same area

3. What about population? Population changes
There are many factors that influence a population
Natural
Unnatural
Population density has a great impact on ecosystems

4. 3 important characteristics of Population
Geographic Distribution
Density
Growth Rate
***Population Age structure is also an important characteristic

5. Geographic Distribution
AKA Range
Describes an area inhabited by a population
Can vary
Few cubic centimeters
Kilometers of the ocean

8. Density # of individuals per unit area Low density High density
Cactus in desert
High density
Other desert plants and succulents

10. Math Time Formula for calculating population density
Population density=Number of individuals
units area
Problem: Suppose there are 150 bullfrogs living in a pond that covers an area of 3 square kilometers. What is the density of the bullfrog population?
50 bullfrogs per square kilometer

11. Growth Rate
Many factors affect growth rate

12. 3 Factors that affect population size
# of births
# of deaths
# of individuals that enter or leave population
Population will increase or decrease depending on # of individuals added or removed

13. What happens to the population when we….
Have more births than deaths?
Population increases
Have more deaths than births?
Population decreases
Have equal amounts of births and deaths?
Population remains constant

15. Immigration “im”= in Migrate= to move from one place to another
Immigration is the individual movement into an area
Animals in search of mates and food in new areas

20. Emigration “E” means ‘out’
Migrate means to move from one place to another
Emigrate means individuals moving out of one place and into another
Young wolves and bears leaving as they mature
Shortage of food

21. Two types of growth Exponential growth Logistic growth
Individuals reproduce at a constant rate
Logistic growth
Occurs when a populations growth slows or stops after a period of exponential growth

22. Exponential Growth
Occurs under ideal conditions with unlimited resources
Think about exponents in math….
Starts slowly then sky rockets to infinity
Our graph will look like a J
Bacteria

23. Lets look at bacteria… Bacteria reproduce by splitting in half
Bacteria have a doubling time of 30 minutes
If you start will one bacterium, how many bacteria will there be after the first 30 minutes? 2
After an hour? 4
After an hour and a half? 8
After two hours? 16
After 15 hours?
Over a billion

25. Logistic Growth
As resources become less available, the growth of the population slows or stops
S-shape curve
What we usually see in nature

27. Carrying Capacity
The largest number of individuals that a given environment can support
The part of the logistic graph after the exponential growth…the flattening out
The point at which this flat line reaches the y-axis is the size of the population when the growth rate reaches zero
This doesn’t mean the population stops growing
Many factors slow the growth of plants and animals…