Survivorship Curves
Introduced| English | Meaning |
|---|---|
| survivorship curve/səˈvaɪvəʃɪp kɜːv/ | A graph showing the proportion or number of a cohort still alive at successive ages. |
When do organisms die?
- Some species lose most of their young early; others survive to old age.
- A survivorship curve captures this pattern.
- It plots how many of a group are still alive at each age.
- The shape of the curve reveals a species' whole life strategy.
Type I: die late
- A survivorship curve 存活曲线 shows survivors versus age.
- A Type I curve stays high, then drops steeply at old age.
- Most individuals survive youth and die old.
- Humans and elephants show Type I — few young, heavily cared for.
Type I, II and III survivorship curves
A survivorship curve shows…
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A survivorship curve plots how many individuals of a group are still alive at each age.
Type II: steady loss
- A Type II curve falls at a steady, straight rate.
- Individuals have about the same chance of dying at any age.
- Many birds and small mammals show this pattern.
- It sits between the two extremes.
A Type I curve (like humans) means most individuals…
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Type I (humans, elephants): low early death, most survive to old age — typical of K-strategists.
Frogs and fish, whose young die in huge numbers, show a Type ____ curve.
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Type III (frogs, fish): very high early death, but a few survive — typical of r-strategists.
Type III: die early
- A Type III curve drops steeply at the start, then flattens.
- Most young die very early, but the few survivors live on.
- Frogs, fish, and oak trees (with countless seeds) show Type III.
- These are r-strategists: many offspring, little care.
Which survivorship type?
Sort each species by when in life most of its members die - late (I), steadily (II), or early (III).
Type I survivorship curves usually belong to r-selected species.
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False. Type I (most survive to old age) fits K-selected species with few, cared-for young. r-selected species, with many uncared-for young, show Type III.
Select all true statements about survivorship curves.
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Different species have very different curves. The other three are correct.
Survivorship type links to reproductive strategy. Type I goes with K-selection (few, well-cared-for young that survive). Type III goes with r-selection (many young, most dying early). Do not mix them up — the curve tells you the strategy at a glance.
An oak tree's survivorship:
- One oak drops thousands of acorns each year.
- The vast majority are eaten or never sprout — a steep Type III drop.
- But a rare few grow into mighty trees that live for centuries — the flat tail of the curve.
A survivorship curve plots how many of a group survive to each age. Type I (humans) means most survive to old age, linked to K-selection; Type II means a steady death rate; Type III (frogs, fish) means most die young, linked to r-selection. The curve's shape reveals a species' life strategy.