Topic 10 -Age Population Structure

Question 1

Age structure

Answer 1

The number of different age classes and the number of individuals in each age class

Question 2

Age class

Answer 2

A discrete grouping for individuals born at approximately the same time

Question 3

Cohort

Answer 3

Individuals that make up an age class

Question 4

Birth rate

Answer 4

The number of female offspring produced per female in a particular age class

Question 5

The number of offspring will differ among________ (e.g. age at sexual maturity, sexual senescence/menopause)

Answer 5

Age class

Question 6

Why are we concerned primarily with females when looking at birth rate

Answer 6

Birth rate is limited by the number of females and it’s difficult to quantify the contribution of each male

Question 7

Death rate

Answer 7

The number of females that die per age class in the population

Number of individuals dying will differ among age classes

Question 8

Survivorship curves

Answer 8

Number of individuals of life versus age

Three possible hypothetical curves few populations fit one precisely

Question 9

Life table

Answer 9

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

Question 10

Cohort (dynamic) life tables

Answer 10

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

Question 11

Static (time specific) life tables

Answer 11

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)

Question 12

Biologists age organisms in several ways and depending on the species

Answer 12

Such as change of feathers

tree rings

Rings in fish bones

Question 13

What is X in a cohort life table

Answer 13

X equals the age class

Question 14

What is Nx in a cohort life table

Answer 14

Total number of individuals at each age X

Question 15

What is Fx in a cohort life table

Answer 15

Total number of offspring produced during each age class x

Question 16

Differences in the count for the two tables

Answer 16

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

Question 17

What is lx in a cohort life table

Answer 17

Proportion of the original cohort surviving from birth to age X (survivorship)

lx= nx/n0

Question 18

What is dx in a cohort table

Answer 18

Proportion of the original cohort dying during each age class

dx=lx-l(x+1)

Question 19

What is qx in a cohort life table

Answer 19

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

Question 20

What is bx in a cohort life table

Answer 20

Individual fecundity or birth rate (age specific birth rate)

the mean number of offspring produced per surviving individual

bx=Fx/nx

Question 21

Although birth rate may increase with age survivorship generally will _______ with age

Answer 21

Decrease

Question 22

Ro in the cohort life table

Answer 22

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

Question 23

Ro may change for different generations, to determine how population size will change over the long term we need

Answer 23

Many generations of data