Is Plant Fitness Proportional to Seed Set? An Experiment and a Spatial Model

Area of Science:

• Ecology
• Evolutionary Biology
• Plant Sciences

Background:

• Individual differences in fecundity are often used as a proxy for overall fitness.
• This proxy can be biased if density-dependent interactions affect offspring survival and reproduction differently based on parental fecundity.
• Understanding these effects is crucial for accurate fitness assessments in natural populations.

Purpose of the Study:

• To investigate density-dependent effects on offspring success in plants.
• To determine if sibling interactions modify the relationship between parental fecundity and offspring fitness.
• To assess how spatial factors influence fitness estimations based on fecundity.

Main Methods:

• Experimental sowing of seeds from high- and low-fecundity Ipomopsis aggregata (scarlet gilia) plants to mimic overlapping seed shadows.
• Utilized a genetic marker to track offspring success to the flowering stage over multiple years.
• Developed a mathematical model incorporating seed shadow geometry and limited survival to predict offspring ratios.

Main Results:

• Empirical data showed offspring success ratios closer to 1.42:1, deviating from the expected 2:1 ratio without density dependence.
• Model predictions aligned with empirical observations, indicating weaker selection than initially suggested by fecundity alone.
• Both juvenile offspring numbers and flower production supported the model's predictions.

Conclusions:

• Fecundity alone is an unreliable proxy for fitness when density-dependent effects are present.
• Spatial relationships between parents and seed dispersal patterns significantly impact the interpretation of fitness based on fecundity.
• The study highlights the importance of considering ecological context for accurate evolutionary fitness assessments.