APES Video Notes 3.3 - Survivorship Curves

Survivorship Curves

• Definition: A survivorship curve plots the number of individuals still alive at each age for a cohort (group born at the same time).

• Y-axis: Survivorship (number or proportion of individuals alive).

• X-axis: Age of individuals (time).

Chapter 2: Objectives

• Key Points to Understand:

  • A survivorship curve shows survival rates for a cohort.

  • Three basic types of survivorship:

    • Type 1: High juvenile survivorship, lower mortality in early life (K selected species).

    • Type 2: Constant mortality rate throughout life (birds, rodents).

    • Type 3: Low juvenile survivorship, high mortality early on (R selected species).

• Survivorship Curves:

  • Type 1 curve is relatively flat at the start with steep decline in older age.

  • Type 3 curve shows fast decline early in life, with few surviving to adulthood.

Chapter 3: Survivorship Types

Type 1 Survivorship

• Characteristics: High parental care leads to high survivorship in early and midlife.

• Examples:

  • Grizzly Bears: Protecting cubs from threats.

  • Chimpanzees: Nursing and safeguarding offspring.

• Decline: Sharp decrease in survivorship as individuals reach old age.

Type 2 Survivorship

• Characteristics: Intermediate parental care, with somewhat constant mortality.

• Examples: Birds and rodents experienced consistent decline, influenced by vulnerability to predators and environmental factors.

Type 3 Survivorship

• Characteristics: Low parental care resulting in high mortality rates for young.

• Examples:

  • Insects, Fish, and Plants: High number of offspring compensates for low survivorship.

• Lifespan Pattern: Most die in early life but some survive to slow decline in adulthood.

Graph Interpretation

• Graphs show survivorship relative to the overall lifespan of the species depicted.

• Units of age on the x-axis are relative, allowing for comparison across species with vastly different maximum lifespans.

• Insights:

  • Example: Dandelions vs. Whales: different lifespans but percentage reaching maturity is comparable on a relative scale.

Conclusion

• FRQ Practice: Analyze and describe trends in survivorship data. Justify the type of survivorship curve represented.

• Closing: Reminder to engage with content and subscribe for updates.