1. Lesson 4.2 Describing Populations
1900 to NY white-tailed deer population grew from 20,000 to over 1 million
Metropolitan areas have densities of over 100 deer per sq mi

2. Population Size Number of individuals in a population at a given time
Lesson 4.2 Describing Populations
Population Size
Number of individuals in a population at a given time
Sudden, dramatic decrease in population size can indicate an unhealthy population headed toward extinction
Ecologists use sampling techniques to estimate population size
Did You Know? The passenger pigeon was once North America’s most abundant bird. Hunting drove them to extinction in less than 100 years.
Counting Laysan Albatross Nests

3. Population Density How crowded a population is
Lesson 4.2 Describing Populations
Population Density
How crowded a population is
Larger organisms; lower population densities
Low population density: More space, resources; finding mates can be difficult
High population density: Finding mates is easier; more competition; more infectious disease; more vulnerability to predators
Northern pintail ducks

4. Population Distribution
Lesson 4.2 Describing Populations
Population Distribution
How organisms are arranged within an area:
Random distribution: no particular pattern
Uniform distribution: evenly spaced
Clumped distribution: grouped near resources; most common in nature

5. Age Structure Number of organisms of each age group
Lesson 4.2 Describing Populations
Age Structure
Number of organisms of each age group
Used to predict future population growth

6. Sex Ratios Proportion of males to females Age structure diagrams
Lesson 4.2 Describing Populations
Sex Ratios
Proportion of males to females
Age structure diagrams
For a monogamous species, the ideal sex ratio is 50:50.