Find when in life most of the deaths happen
- The idea
- Predict
- See it
- Why
- Check
The idea
“If two curves start and end at the same numbers, or both have one steep drop, they're the same type.”
You grab what stands out on the graph, like where it ends or one big drop. Two opposite types can share both.
The short version
The mistake: If two curves start and end at the same numbers, or both have one steep drop, they're the same type.
What's actually true: A survivorship curve's type depends on when in the life span most individuals die.
- A survivorship curve follows a cohort, a group born at the same time, and shows how many are alive at each age.
- Type I keeps most individuals alive until late in life, as in humans. Type III loses most of them very young, as in many fish.
- Type II loses the same fraction in every age interval. On the usual log-scale graph it is a straight line.
On the exam: Find the ages where most of the cohort died. Early means Type III. Late means Type I.