1. Carrying Capacity How Populations Grow

2. Population Density – the number of individuals in an area

3. Number of births Number of deaths Emigration (out) & Immigration (in)
Population Growth
Number of births
Number of deaths
Emigration (out) & Immigration (in)

4. In Stokes County, the population was 47,401 in 2011
In Stokes County, the population was 47,401 in babies were born (birthrate = 9 per 1000 people). 474 people died (death rate = 10 per 1000 people). What is the growth rate for the county?
Birth rate (b) − death rate (d) = rate of natural increase (r).
9 – 10 = -1
-1 per 1000 people
-1/1000 = or -.1% rate of increase
So it is a negative growth rate!!!!
Positive Growth rate = population increase Negative Growth rate = decrease

5. Human Population
Human population is growing exponentially on our planet.
World Population over 6 billion

6. Exponential Growth –reproduce at a constant rate
Exponential Growth –reproduce at a constant rate. Occurs under ideal conditions (no limits)
J-shape curve

7. Histogram—a type of bar graph
Age Structure (aka Age-Sex) Histograms - Shows the number of people by gender and by age in a given population.
Example:

8. How do you read this thing?
Let’s do an example: Why is Mexico’s population growing rapidly and Sweden’s not growing at all?

9. Having a wide base and a thin top to the histogram shows that a lot of people are being born and few will be dying off (Mexico). If the chart is fairly consistent all the way up, there is very little change taking place (Sweden).

10. Carrying capacity Maximum population size an environment can sustain
When a population out grows the carrying capacity then limiting factors may come into effect.

11. Exponential Growth vs. Carrying Capacity

12. Limiting Factors Factors that cause population growth to decrease
Can be biotic or abiotic
Biotic such food source of plants or animals
Abiotic such as light, temperature, soil, weather

13. 2 kinds of limiting factors
Density-dependent – depends on population size
Examples – disease, parasites, competition, predators, and food

14. Density-independent does not depend on population size
can affect populations regardless of their density
Usually abiotic factors such as weather, climate, natural disasters (floods, volcanic eruptions, etc)