Life Tables Flashcards
Define demography
the study of the processes that change the size of a population (ex. birth, death, and dispersal) with particular respect to sex and age
Define surviorship
the probability of a newborn individual living to a particular age
Define mortality rate
the probability of dying at a particular age
What is the slope related to on survivorship graphs (# of survivors vs. age) and explain
related to the mortality rate
a steep slope implies high mortality vs. shallow slope meaning lower mortality rate
Define life tables function
allow for enumerating age and sex specific vital rates.
allow for understanding age-structured population growth and life-history evolution
In life tables, how is lx often displayed
by multiplying by 1000 often shown on log scale
sometimes survivorship curves are separated by _____
cohort (age or by year)
Why is the correction factor necessary in the life expectancy equation
because without it, is saying that all individuals are dying at the end of their lifespan
Explain the 3 types of survivorship curves
Type 1 = age specific mortality INCREASES with age (humans)
Type 2 = age specific mortality is CONSTANT with age (squirrels)
Type 3 = age specific mortality DECREASES with age (turtles)
When generating a life table, we either need _____ or ____ data
number surviving to interval
number dying during interval
what kind of organisms are cohort life tables typically applied to
short lived and/or sessile organisms that can be tracked reliably for their whole lives
Cohort life tables can be applied to population at any phase of population ______
growth
(growing, shrinking, stationary)
Cohort life tables are typically the _____ but they usually require ____
most powerful and accurate
more effort
Define static life tables
data is collected at a single point in time, applied to long-lived and/or mobile organisms that are difficult to track reliably their whole lives
What are the subtypes of static life tables
- time specific 2. stationary based on ages at death within a population
Define time-specific life tables
builds life table by estimating the survival of individuals of known age during a single time interval, uses yearly mortality (qx)
What is a stationary life table based on
ages at death within a population, the number dying in each class (Dx)
How was the stationary life table for Dall mountain sheep built
they used the horns of dead sheep to create their data and the total number to create their cohort size
What are the very strict assumptions of the stationary life table example of using Dall mountain sheep
- can accurately age the skulls
- probability of finding skills does not change with age
- population is stationary in size (if the population was growing, young individuals would be overrepresented)
Sx
number alive at the start of interval
Dx
Number dying in interval
Sx-Sx+1
lx
probability of survival from birth to certain interval
Sx/S0
qx
probability of dying in the interval (mortality)
lx-lx+1/lx
dx
fraction dying in the interval
Dx/S0
ex
mean expectation of life
[(sum of all survive of time and older)/survived to that exact time] -0.5
