1. Things To Do Objectives Pick up notes and handouts
Learn about populations
Discuss how a population is limited
Go over carrying capacity

2. Population Ecology
Notes 1

3. Terms:
Species: Organisms that can interbreed and create fertile offspring
Population: A group of interacting individuals
Exponential Growth: Growth pattern where a population grows faster as it increases in size
Carrying Capacity: The number of individuals of a species that an environment can support
Density - Dependent Factor: Factor such as disease, parasites or food supply that has an increasing effect as populations increase
Density - Independent Factor: Factors such as temperature, storms, floods, drought or habitat that disrupt the affects all populations, regardless of their density

4. What is a Population?
It consists of all the individuals of a species that live together in one place at one time.
Every population tends to grow because individuals tend to have multiple offspring
Eventually limited resources in an environment limit the growth of a population
The statistical study of all populations is called demography
Demographers study and predict the composition of a population and how it will change
4 Key Features of Populations
Population Size
Population Density
Dispersion
Growth Rate

5. Size and Density Population Size Population Density
Can affect the populations ability to survive
Studies have shown that very small populations are among the most likely to become extinct
Small populations are prone to interbreeding
Large populations will run out of resources
Population Density
The number of individuals that live in a given area
If the individuals of a population are few and are spaced widely apart, they may seldom encounter one another, making reproduction rare.

6. Dispersion and Growth Rate
The way the individuals of the population are arranged in space
Three Ways
Random Distribution
Even (Uniform) Distribution
Clumped Distribution
Growth Rate
Number of Births - Number of Deaths = Growth Rate
Positive Growth Rate: More births than deaths, population grows
Negative Growth Rate: Less births than deaths, population declines
Zero Growth Rate: Number of births and deaths are about the same, population remains the same

7. How Fast does a Population Grow?
Reproductive Potential: The maximum number of offspring each individual of a population can produce
Varies for each species
Examples
750 years for elephants to produce 19 million offspring
2 weeks for bacteria to produce 19 million offspring

8. Population Models
Hypothetical population that attempts to exhibit the key characteristics of a real population
They use models to predict and simulate growth, dispersion, size and density
Populations don't grow in a linear fashion but exponentially
Example:
1 bacteria becomes 2
2 bacteria become 4
4 bacteria become 16
16 bacteria become 256

9. Limiting Factors
These are biotic or abiotic factors that limit the existence, reproduction, growth, numbers, and distribution of an organism
Think about this:
A female sea turtle can lay about 2,ooo eggs in her lifetime
If all of the eggs survived, there would be huge increases in numbers every year
Why doesn't the population of sea turtles increase rapidly each year?

10. Limiting Factors Populations rarely grow to their capacity
Carrying Capacity
The maximum population of a specific species that the ecosystem can support indefinitely
There are many factors that can limit growth:
Resources
Competition
Disease
Natural Disaster

11. Resources and Competition
Resource availability is going to be the biggest limiting factor
Example:
Plants need 8 1/2 hours of sunlight, 1/4 gallon of water, and 10 different mineral nutrients a day
The ecosystem can provide 12 hours of sunlight, 1/2 gallon of water and 9 mineral nutrients a day
What is the limiting factor: sunlight, water or minerals?
Competition
There can be competition within a population
Competition can exist among species as well

12. Population Regulation
Causes of death in a population
Density - Dependent
Death occurs more rapidly in a dense population rather than a sparse one
This can come from resource depletion as well
Density Dependent Factors:
Competition
Predation
Disease
Parasitism
Crowding
Stress
Example:
14th Century saw the Bubonic Plague
Cities were more affected than rural communities

13. Population Regulation
Density - Independent
Death occurs regardless of the density of the population
It usually includes environmental conditions like weather
Density Independent Factors:
Natural Disasters
Temperature
Sunlight
Human Activities
Physical Characteristics
Behaviors