The opportunity for selection: A slippery concept in ecology and evolution

Area of Science:

• Evolutionary ecology
• Quantitative genetics
• Population biology

Background:

• Natural selection requires fitness variation among individuals.
• The opportunity for selection (I) quantifies this fitness variance.
• The historical use of I in evolutionary ecology is debated.

Purpose of the Study:

• To critically evaluate the use and misuse of the opportunity for selection (I) and related metrics.
• To clarify the relationship between fitness variation and actual trait-based selection.
• To investigate factors influencing the magnitude and interpretation of I.

Main Methods:

• Theoretical discussion of the opportunity for selection (I) and its components.
• Analysis of stochastic factors and multiple trait effects on fitness variation.
• Simulations and empirical data analysis using a great tit (Parus major) population study.

Main Results:

• The opportunity for selection (I) does not inherently imply selection is occurring, as fitness variation can be independent of phenotype.
• Selection intensity is upper-bounded by I but limited by stochasticity and multiple traits.
• In great tits, fecundity selection scope was higher using annual recruits vs. fledglings/eggs, suggesting nonrandom juvenile survival.

Conclusions:

• Direct inferences about selection from fitness data alone are unreliable.
• Variation in I, especially when adjusted for mean fitness, can indicate when/where selection is strongest.
• This approach aids research planning and experimental design in evolutionary studies.