Life table

Definition

A demographic summary of age-specific mortality and survival rates within a cohort or population, typically arranged as a table showing the number surviving, dying, and their age-specific probabilities of death at successive intervals. In ecology and entomology, life tables distinguish cohort (horizontal) tables that track a single generation through time from static (vertical, time-specific) tables that sample a population at one moment across all age classes. The table's lₓ column records survivors at age x, dₓ records deaths between ages x and x+1, and qₓ gives the age-specific mortality rate (dₓ/lₓ). Fecundity schedules (mₓ) are often appended to form a complete life table for calculating net reproductive rate (R₀) and intrinsic rate of increase (r).

Etymology

From life + table; coined in demography and adopted into ecology through the work of Raymond Pearl and others in the early 20th century.

Example

A cohort life table constructed for the cabbage aphid (Brevicoryne brassicae) under field conditions might show lₓ declining from 100 neonates to 12 adults at reproductive age, with heavy dₓ losses during the first two instars due to predation by syrphid larvae, yielding a net reproductive rate R₀ = 42 and generation time T = 12 days.

Synonyms

• mortality table
• survivorship schedule

Related Terms

• cohort analysis
• Survivorship curve
• fecundity schedule
• net reproductive rate
• Intrinsic rate of increase
• key factor analysis
• Population dynamics
• stable age distribution

Usage Notes

Ecologists distinguish cohort (horizontal, dynamic, or generation) life tables from static (vertical, time-specific, or current) life tables; the former requires marking or rearing individuals through time, while the latter assumes a stable age distribution. In entomology, life tables are essential for identifying key mortality factors in biological control programs and for predicting outbreak potential. The term actuarial table is reserved for human demography and insurance contexts. Life tables assume age is the primary determinant of mortality risk, which may not hold for arthropods with strong stage-structure effects or diapause.