1. Question
Would you rather be paid $100 a day for a month or 1 penny the first day, 2 pennies the second day, 4 pennies the next day, 8 pennies the next day…etc. for the rest of the month?
EXPLAIN YOUR ANSWER

2. $100 a day equals $3,000 for the month.
Starting with one penny, two pennies on the second day, 4 on the third day, 8 on the fourth day, etc.
1x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2=

3. Population Growth
I will call on a student to give me a beginning population (# between )
I will call on another random student to give me a birth rate (Crude birth rate is the number of births per year per 1000 adults) (# between 5-40)
We’ll put the data into a spread sheet to see what kind of growth occurs

4. population growth.xls

5. Exponential Model of Population Growth
Population increases rapidly with no limit
What will a graph look like?
Rare in nature. Why?
“J” shaped curve
Limit on the amount of resources (food / space)

6. limiting factors
Populations can’t grow exponentially forever because of limiting factors.
Limiting Factors can be:
BIOTIC– predators, food availability, disease, competition from their own species
ABIOTIC– space, water, shelter, nutrients, salinity, temperature.

7. How populations change
INCREASE size DECREASE size
Births
Deaths (mortality)
Immigration
(coming in)
Emigration
(going out/leaving)
Growth rate = (births + immigration) – (deaths + emigration)
If (births + immigration) > (deaths + emigration), population INCREASES
If (births + immigration) < (deaths + emigration), population DECREASES
If (births + immigration) = (deaths + emigration), population stays the same

8. logistic growth AKA “S-curve” or sigmoidal
More realistic model than exponential.
Populations reach carrying capacity.
Carrying capacity- the number of individuals the environment can support over a long time period
What alters the carrying capacity of an environment?

9. Logistic Model of Population Growth
When at carrying capacity,
birth rate is equal to
death rate
Accounts for influence of limiting factors
What will the graph look like?
As population reaches
carrying capacity,
the difference between birth
rate and death rate decreases
When population is small,
birth rate is higher
than death rate
Stretched out “S”

11. Wrap Up
In the Oh Deer activity we learned about biotic and abiotic factors, how they are part of an ecosystem and how they influence the deer population.
In a sentence or two, explain (in general terms) what a limiting factor is and its effect on a population.