APES Video Notes 3.3 - Survivorship Curves

Main ideas & concepts

• Topic focus (3.3 Survivorship Curves): Builds on topic 3.2 (r-selected vs. K-selected species) by connecting reproductive strategy and parental care to offspring survival across age.

Connection to reproductive strategy

• r- and K-selected species differ in how much parental care they provide.
• This difference is reflected in survivorship: how likely offspring are to survive infancy and reach adulthood.

What a survivorship curve shows

A survivorship curve graphs a cohort (a group of individuals of the same species born around the same time).

• Y-axis: number of individuals (or proportion) still alive at each age
• X-axis: time/age (moving right means older)
• Shape of the curve: indicates how quickly individuals die as they age

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Three types of survivorship trends (detailed)

Type 1 survivorship (associated with K-selected species)

• Pattern: High survival early and during midlife, followed by a rapid decline late in life (old age).
• Key reason: High parental care.
• Examples mentioned:
  • Whale
  • Grizzly bear (mother defending cubs)
  • Chimpanzee (mother carrying/protecting while breastfeeding)

Type 2 survivorship

• Pattern: Moderate survival early life, then a steady, relatively constant decline throughout life.
• Key reason: Some parental care, but offspring/young are vulnerable because organisms are typically smaller and/or young are sensitive to threats.
• Examples mentioned:
  • Birds
  • Rodents
  • Baby chick
  • Disease/temperature/predation vulnerabilities are noted.

Type 3 survivorship (associated with r-selected species)

• Pattern: Very high mortality early in life (most die in infancy/childhood), then a slower decline later.
• Key reason: Little to no parental care.
• Compensation strategy: They produce lots of offspring to offset low survival.
• Examples mentioned:
  • Dandelion (illustrates rapid early die-off)
  • Insects
  • Fish
  • Plants
• Emphasis: Few reach middle age; most die early.

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Additional clarification about the graph

• The age on the x-axis uses relative units, not actual lifespan lengths.
  • This means a graph can compare species (e.g., dandelions vs. whales) on the same axis by showing survival relative to each species’ own maximum lifespan.
  • The curve compares proportions reaching relative “maximum age,” not identical real-world ages.

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Objectives / lesson goals (as stated)

Be able to:

• Explain survivorship curves
• Know they show survival rates for a cohort (group born at about the same time)
• Identify three basic survivorship trends: Type 1, Type 2, Type 3
• Understand:
  • K-selected → Type 1 due to high parental care
  • r-selected → Type 3 due to lack of parental care, compensated by many offspring

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FRQ practice (method/instructions presented)

• Task: Data analysis for topic 3.3.
• You must:
  1. Describe the pattern/trend in survivorship shown by the given graph.
  2. Justify which survivorship type (Type 1, 2, or 3) the data represent.

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Speakers / sources featured

• Mr. Sp[e]eds (the video instructor/host)
• No other sources or speakers are identified.