Life History Variation and Reproductive Trade-Offs
Life history variation refers to differences in survival and reproductive strategies among organisms, including when they reproduce, how often they reproduce, and how much energy they invest in each offspring.
In one line: Life history asks: when to reproduce, how often, and how much to invest.
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- Organisms have limited energy, so investment in growth, survival and reproduction involves trade-offs.
- Some species produce many small offspring with low parental care, increasing the chance that at least a few survive.
- Others produce few large offspring with higher investment, improving the survival chance of each offspring.
- Semelparous organisms reproduce once in their lifetime, while iteroparous organisms reproduce repeatedly.
- These strategies are shaped by habitat, predation pressure, resource availability and natural selection.
- Exam questions usually test the logic of trade-off rather than only the names of strategies.
Example
Rule to remember
Key biological rule: energy used for one function, such as producing many gametes or offspring, reduces energy available for another function, such as growth, defence or parental care.
See it worked out
Follow the example line by line, then use the same method on new questions.
Worked example
- 1If a fish releases thousands of eggs with little care, identify the strategy.
- 2It is a many-small offspring strategy because reproductive effort is spread across numerous offspring rather than high care for each one.
Method you can reuse
Visual tip
A simple comparison chart can show semelparity versus iteroparity and many-small versus few-large offspring strategies. No mandatory structural diagram is required.
Check yourself
Answer the question in your head before opening the answer.
Try it yourself
Why do some organisms produce many small offspring instead of a few large ones?
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Common wrong answer
Writing that semelparity means many offspring and iteroparity means few offspring is incomplete; the main distinction is one reproductive event versus repeated reproductive events.
Don't mix this up
Exam tip
Write it in the exam
Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.
How CBSE asks it
Answer plan
- 1
Enough for 1 mark
Life history variation refers to differences in survival and reproductive strategies among organisms, including when they reproduce, how often they reproduce, and how much energy they invest in each offspring.
- 2
Add for 2 marks
Example: Pacific salmon are often used as an example of semelparity because they reproduce once and die soon after. Humans and many mammals are iteroparous because they can reproduce multiple times and invest more care in fewer offspring.
- 3
Add for 3 marks
Organisms have limited energy, so investment in growth, survival and reproduction involves trade-offs.
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