L10 Tosh - Life Tables, Cohorts and Age Structured populations

Question 1

Define mortality

Answer 1

The rate at which individuals die in a population

Question 2

What are the 3 mortality trend types a population can follow?

Answer 2

Type 1: most individuals die at an old age

Type 2: individuals doe at a constant rate throughout their lives

Type 3: most individuals die young

Question 3

When is a cohort table used?

Answer 3

• they help identify key areas of age specific mortality and fecundity
• they are used where animals breed continuously or where generations overlap

Question 4

What is a cohort?

Answer 4

a group of animals all born during the same time interval

Question 5

What do cohort life tables show?

Answer 5

• changing patterns of mortality with age/stage of the animal
• allows construction of a survivorship curve
• birth rates also measured - construct fecundity schedules
• they are simplest with animals that have an annual life cycle - insects and plants

Question 6

Why scale a cohort table?

Answer 6

• easier to interpret a percentage

- can compare data from different years

Question 7

How are cohort tables relative to the next stage?

Answer 7

• they assume mortality factors are sequential

- log A - log B is the same as A/B

Question 8

What would the sum of all the K values in a cohort table tell you?

Answer 8

Summed to show overall mortality

Question 9

What can K values be used for?

Answer 9

• Summed to show overall mortality
• compared over a range of years to identify a key factor
• can be compared with population size to identify a regulating factor

Question 10

In a graph of the K values, what line is the key factor?

Answer 10

Key factor is the line that is most similar in shape/ most influential

Question 11

In a graph of the K values, what line is the regulating factor?

Answer 11

For the regulating factor you plot a graph of K factors against population size.

If there is a correlation this suggests that it is a source of mortality

Question 12

What are the 2 types of life tables?

Answer 12

1. Fixed life table - examine the population in a particular year (cohort), through to death for every individuals in that cohort
2. Static life table - the whole animal population is studied within an single year

Question 13

Why are there 2 types of life table?

Answer 13

It depends on the life cycle of the animals involved:

• Species with a simple annual life cycle are much easier to analyse as a cohort - fixed
• specie that live several years, especially birds and mammals, would need to mark or tag individually, therefore static is easier