Snared in an Evil Time: How Age-Dependent Environmental and Demographic Variability Contribute to Variance in...

Area of Science:

• Ecology
• Evolutionary Biology
• Life History Theory

Background:

• Understanding drivers of lifetime success is crucial in ecology and evolutionary biology.
• Distinguishing between individual quality and external factors (luck) in determining success is a long-standing question.
• Previous work partitioned "luck" in lifetime outcomes, but lacked detailed analysis of environmental variation and demographic components.

Purpose of the Study:

• To quantify the relative contributions of innate individual quality versus external events (luck) to lifetime success.
• To investigate how external events and chance interact with development (survival and growth) to influence success.
• To extend previous models by incorporating environmental variation and subdividing demographic luck into survival and growth components.

Main Methods:

• Developed an extended age-partitioning framework to analyze lifetime outcomes.
• Incorporated effects of external environmental variation into the model.
• Subdivided demographic luck into contributions from survival and growth.
• Applied the methods to four diverse case studies.

Main Results:

• Luck in survival, growth, or environmental variation can be the dominant driver of success, varying by life history.
• Innate individual quality was consistently a lesser driver of success compared to various forms of luck.
• Different forms of luck have distinct temporal importance, peaking at early ages and near the onset of success (e.g., reproduction).
• Favorable environmental years can facilitate early-life advantages, while survival luck is key for capitalizing on opportunities.

Conclusions:

• External factors and chance play a more significant role in determining lifetime success than innate individual quality.
• The interplay between luck, development, and environmental context is critical for understanding life history outcomes.
• The timing and type of luck are crucial, with early-life events and opportunities near success thresholds being particularly sensitive to chance.