1. IS3-4 Population And Ag Unit Lesson 3
Ms Dallara

2. Notes
Populations
Introduction to Population Dynamics

3. I. Populations The world is divided into millions of species.
A. What is a population?
The world is divided into millions of species.
Within a species, a population is a group of individuals that are actually available to each other for mating.
A species may be spread across the globe, while a population tends to cluster together.

4. I. Populations
B. Examples

5. I. Populations C. Population Dynamics
Populations grow when birth rate + immigration rate (# of organisms moving into a population) > death rate + emigration rate (# of organisms moving out of a population)
Populations decline when birth rate + immigration rate (# of organisms moving into a population) < death rate + emigration rate (# of organisms moving out of a population)

6. This type of growth is called exponential growth.
II. Population Growth
Populations and Resources
Resources determine how a given population will grow.
In general, any population of organisms with plenty of resources and ideal conditions tends to grow fast.
This type of growth is called exponential growth.

7. II. Population Growth Doubling Time
Exponential growth has a fixed doubling time. There is a certain number of days, or months, or years in which the population doubles.

8. II. Population Growth C. Exponential Growth
At first the population grows slowly, but at some point it takes off.

9. III. Limiting Factors
A. No population can continue exponential growth forever: resources are finite.
1. Resources, matter and energy in short supply limit how large a population can grow, therefore resources can be limiting factors.

10. a. examples: competition, predation, parasitism and crowdingB.
1. Density-dependent limiting factors control population size when a population is large and crowded.
a. examples: competition, predation, parasitism and crowding
2. Density-independent limiting factors control population size regardless of whether a population is large or small.
a. examples: natural causes such as geothermal activity, extreme weather

11. Marin County Stats

12. IV. Carrying Capacity & Population Growth
Limiting factors determine the carrying capacity, or the number of individuals in a population that can be sustained indefinitely in a given ecosystem.

13. IV. Carrying Capacity & Population Growth
When a population is small compared to the carrying capacity, it grows rapidly. What happens next depends on many factors.

14. IV. Carrying Capacity & Population Growth
S Curve
The population slows as it approaches the carrying capacity and levels off, reaching a steady state.

15. IV. Carrying Capacity & Population Growth
J Curve
A period of rapid population increase followed by collapse.
Population growth disrupts the ecosystem so badly that its carrying capacity is reduced, and the species suffers a die-off from which it never fully recovers.

16. IV. Carrying Capacity & Population Growth
J Curve
Example