Selection in a population
Environmental conditions do not affect every phenotype equally. Factors such as predation, disease and competition can act as selection pressures, causing differences in survival and reproductive success.
Individuals whose phenotypes provide a selective advantage are more likely to reproduce successfully. Their favourable alleles are consequently represented more often in the next generation, so their frequency in the gene pool can rise over time.
Selection pressures in context
| Environmental factor | Type | Possible effect on lions |
|---|---|---|
| Competition for food | Biotic | Individuals that fail to obtain sufficient prey are less likely to survive. |
| Competition for mates | Biotic | Males that do not gain access to females have reduced reproductive success. |
| Water availability | Abiotic | Severe shortage of water can reduce survival through dehydration. |
| High temperature | Abiotic | Overheating can restrict hunting and reduce the opportunity to obtain food. |
Natural selection therefore acts on existing variation and produces differential reproductive success, which can alter allele frequencies across generations.
Exam Tip: Avoid saying that an advantageous phenotype guarantees survival. State that the phenotype makes an individual more likely to survive and reproduce, and link this to inheritance of the favourable allele.