Selection pressures and sexual selection
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Question
What is a selection pressure?
Answer
Any environmental factor that affects an organism's chance of **surviving and reproducing**, so it decides which traits are favoured.
Question
What is an abiotic selection pressure? Give examples.
Answer
A **non-living** factor — e.g. **temperature, drought, salinity, light, pH**.
Question
What is a biotic selection pressure? Give examples.
Answer
A pressure from **other organisms** — e.g. **predators, parasites/disease, competition** for food or mates.
Question
What is sexual selection?
Answer
Selection for traits that raise **mating success** (getting a mate) rather than survival.
Question
Name the two routes of sexual selection.
Answer
**Mate choice (intersexual)** — one sex chooses showy partners; and **mate competition (intrasexual)** — members of one sex fight for mates.
Question
What kind of trait does sexual selection produce?
Answer
Showy or costly mating traits — **bright plumage, antlers, horns, large size, courtship displays**.
Question
Why does a costly trait like a peacock's tail spread despite lowering survival?
Answer
The **gain in mating success outweighs the survival cost**, so males with it father more offspring.
Question
What does the command term 'Evaluate' require?
Answer
Weigh a point **for** and a point **against**, then reach a **balanced judgement** — not a simple yes/no.
Question
Is competition for mates an abiotic or biotic pressure?
Answer
**Biotic** — it involves other living organisms (rivals and potential mates).
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Topic 4.10 hub
Natural selection
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