AP Environmental Science: Unit 3 (Populations)

K-Selected Species

• “Quality”

• Few offspring

• Lots of prenatal care

• Long lifespan

• Produce few offspring at a time

• Usually reproduce many times

• More likely to be disrupted by environmental change

Examples of K-Selected Species

• Most mammals

• Birds

r-Selected Species

• “Quantity”

• Many offspring at once

• Little to no prenatal care

• Usually only reproduce once

• Short reproduction time and lifespan

• Most likely to be invasive

• Better suited for rapidly changing environmental conditions

Examples of r-Selected Species

• Insects 

• Fish

• Plants

Survivorship Curve

Line that shows a cohort’s survival rate in a population from birth to death.

Characteristics of a Type I Species

• Mostly K-selected species

• High survivorship early in life because of prenatal care

• High survivorship in mid-life because of big size and defensive behavior

• Rapid decrease in survivorship in late life because of old age

• Most mammals

Characteristics of a Type II Species

• In between r and K-Selected Species

• Steadily decreasing survivorship throughout life 

• Squirrels 

Characteristics of Type III Species

• Mostly r-Selected Species

• Low survivorship in life because of little to no prenatal care

• Few make it to mid-life

• Slow, steady survivorship decline

• Insects, Fish, Plants

Carrying Capacity (k)

The maximum number of individuals in a population that an ecosystem can support with its resources.

Population Overshoot

When a population briefly exceeds the Carrying Capacity.

• Consequence: Resource depletion

Population Die-off

The sharp decrease in population size when resource depletion leads to many individuals dying.

Characteristics of a Population

• Size (N): Total number of individuals in a given area at a given time.

• Density: Number of individuals per area.

• Distribution: How individuals in a population are spaced out.

Types of Distribution

• Random (e.g. trees)

• Uniform (e.g. territorial animals)

• Clumped (e.g. herd/group animals)

Density-Dependent Factors

Factors that influence population growth based on size