Population Ecology Human Survivorship Population age structure Life

Population Ecology: Human Survivorship

Population age structure

Life tables provide age-specific mortality and survival • Life-table: age-specific account of mortality • Cohort: group of individuals born in the same time period Age (x) Individuals (nx) 0 530 1 159 2 80 3 48 4 21 5 5 • A cohort of 530 coquis from Luquillo, the fate tracked until all indiv died • Of the original 530 individuals born, only 159 survived to age 1. • Of the 159 individuals, only 80 survived to age 2. • Of the 80, only 48 survived to age 3.

Survivorship • Suvivorship (lx): probability at birth of surviving to given age (x) • Expresses the number of individuals surviving to any given age as a proportion of the original cohort size (nx/n 0) Age (x) Individuals (nx) Survivorship (lx) 0 530 1. 0 1 159 0. 3 2 80 0. 15 3 48 4 21 5 5

Number of deaths Age (x) Individuals (nx) Survivorship (lx) Deaths (dx) 0 530 1. 0 371 1 159 0. 3 79 2 80 0. 15 32 3 48 0. 09 4 21 0. 04 5 5 0. 01

Mortality rate: deaths/alive # individuals that died during any given time (dx) divided by # alive at beginning of that interval (nx) Age (x) Individuals (nx) Survivorship (lx) Deaths (dx) Mortality rate (qx) 0 530 1. 0 371 0. 70 1 159 0. 3 79 0. 50 2 80 0. 15 32 0. 40 3 48 0. 09 27 4 21 0. 04 16 5 5 0. 01 5

Coqui life table Age (x) Individuals (nx) Survivorship (lx) Deaths (dx) Mortality rate (qx) 0 530 1. 0 371 0. 70 1 159 0. 3 79 0. 50 2 80 0. 15 32 0. 40 3 48 0. 09 27 0. 55 4 21 0. 04 16 0. 75 5 5 0. 01 5 1. 0

Theoretical Survivorship Curves

Methods for Constructing Survivorship Curves (1) Cohort (dynamic) life table: • Follow population life (birth/hatching/germination) to death (2) Static life table: • Age at death of individuals in a population • Snapshot: count number of individuals alive in each age class at one point in time

Assumptions for Constructing Survivorship Curves • Stable age distribution • What does this mean? • Each age class sampled in proportion to its numbers in population • Population size is constant • What does this mean? • Mortality/birth rates constant over time

Static Method – Pick one of three approaches 1. Ages at death • Gather data from visit(s) to cemetery or online cemetery records • Select two groups you’d like to compare (independent variable) • Record birth/death year of 200+ individuals in each group, calculate age at death 2. Snapshot of age structure • Gather data from US Census records • Select two groups you’d like to compare (independent variable) • Record ages at death of 200+ individuals in each group 3. Compare approach #1 and #2 • Groups: same group, different data sources • Data collection combination of approaches #1 and #2

Timeline • Lab Today (2/9): • Pick your approach and your group • Pick your variables/groups • Develop hypothesis, prediction, and rationale – obtain approval before you leave • Homework between now and next lab: • Gather data for your two groups • Lab Next Week (2/16): • • Work in groups to compile and organize data, plot survivorship curves Work on oral presentation Oral Presentations Peer Review of Presentations