Topic 10 -Age Population Structure Flashcards
Age structure
The number of different age classes and the number of individuals in each age class
Age class
A discrete grouping for individuals born at approximately the same time
Cohort
Individuals that make up an age class
Birth rate
The number of female offspring produced per female in a particular age class
The number of offspring will differ among________ (e.g. age at sexual maturity, sexual senescence/menopause)
Age class
Why are we concerned primarily with females when looking at birth rate
Birth rate is limited by the number of females and it’s difficult to quantify the contribution of each male
Death rate
The number of females that die per age class in the population
Number of individuals dying will differ among age classes
Survivorship curves
Number of individuals of life versus age
Three possible hypothetical curves few populations fit one precisely
Life table
Tabulation of birth and death of each each class in a population
Allows us to quantify whether the size of the population is increasing, stable or decreasing
Cohort (dynamic) life tables
Will follow one cohort (individuals within an age class) from birth to death
Determined B and D in each age class, better for immobile species
Difficult for highly mobile animals and can take a long time to collect data depending on the lifespan
Static (time specific) life tables
Snapshot of the population at one point in time
Estimate death by determining the age specific survival independently for each age class at a specific time
Better for highly mobile animals.
Difficult to determine ages of all individuals
Underlying assumption: stable age structure (number of individuals in each age class stays the same through time)
Biologists age organisms in several ways and depending on the species
Such as change of feathers
tree rings
Rings in fish bones
What is X in a cohort life table
X equals the age class
What is Nx in a cohort life table
Total number of individuals at each age X
What is Fx in a cohort life table
Total number of offspring produced during each age class x
Differences in the count for the two tables
If cohort count the number of individuals remaining from the original cohort of such number
if a static life table count all individuals in each age class in one year
What is lx in a cohort life table
Proportion of the original cohort surviving from birth to age X (survivorship)
lx= nx/n0
What is dx in a cohort table
Proportion of the original cohort dying during each age class
dx=lx-l(x+1)
What is qx in a cohort life table
Proportion of the original cohort dying versus surviving (age specific mortality rate)
qx=dx/lx
Indicates the intensity of mortality in a particular age cannot be summed
What is bx in a cohort life table
Individual fecundity or birth rate (age specific birth rate)
the mean number of offspring produced per surviving individual
bx=Fx/nx
Although birth rate may increase with age survivorship generally will _______ with age
Decrease
Ro in the cohort life table
The net reproductive rate
The sum of mean number of offspring produced per original individual during each age class before death
Ro = sum of lxbx
Ro may change for different generations, to determine how population size will change over the long term we need
Many generations of data
