L10 Tosh - Life Tables, Cohorts and Age Structured populations Flashcards Preview

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Flashcards in L10 Tosh - Life Tables, Cohorts and Age Structured populations Deck (13)
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1
Q

Define mortality

A

The rate at which individuals die in a population

2
Q

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

A

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

3
Q

When is a cohort table used?

A
  • they help identify key areas of age specific mortality and fecundity
  • they are used where animals breed continuously or where generations overlap
4
Q

What is a cohort?

A

a group of animals all born during the same time interval

5
Q

What do cohort life tables show?

A
  • 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
6
Q

Why scale a cohort table?

A
  • easier to interpret a percentage

- can compare data from different years

7
Q

How are cohort tables relative to the next stage?

A
  • they assume mortality factors are sequential

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

8
Q

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

A

Summed to show overall mortality

9
Q

What can K values be used for?

A
  • 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
10
Q

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

A

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

11
Q

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

A

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

12
Q

What are the 2 types of life tables?

A
  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
13
Q

Why are there 2 types of life table?

A

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