Lecture 10

Question 1

What is mortality? What does it provide?

Answer 1

The rates at which individuals die within a population, provide information about its functioning

Question 2

Pearl (1928) argued that there were 3 types of mortality curves. What are these?

Answer 2

. Type 1: low early mortality, high late mortality. Typical of humans in developed world (Most individuals survive until old age)
. Type 2: probability of death remains constant with age, leading to a linear decline in survivorship (have a constant chance of dying throughout their lives)
. Type 3: characteristic of most animal populations. Very high early mortality, but those that remain have high rate of survivorship (individuals usually die young) e.g. many species of fish

Question 3

What do mortality/ survivorship curves reflect?

Answer 3

Particular habitat conditions for the population, and density

Question 4

What is a cohort?

Answer 4

. A group of animals all born during the same time interval (e.g. all kids born in the UK this year)
. Track the date of all the individuals within this cohort from birth until death

Question 5

What are cohorts and life tables used for/ help with?

Answer 5

. Widely used when studying animal populations
. Help identify key areas of age-specific mortality and fecundity
. Used where animals breed continuously, or where generations overlap
. Aid decisions on management of animal populations

Question 6

Describe diagrammatic life tables

Answer 6

. Relatively easy to follow

. Can be more difficult to analyse and make predictions

Question 7

Describe cohort life tables, give examples

Answer 7

. Show changing patterns of mortality with age or stage of the animal
. Allows us to construct survivorship curves
. Births amongst different ages also measured
. Allows us to construct fecundity schedules
. Simplest with animals with an annual life-cycle (produce young ever year)
. E.g. most insects, annual plants etc.)

Question 8

What are k-values (killing factors)?

Answer 8

Scaled measures of impacts of mortality at each stage relative to the next stage

Question 9

Why are k-values (killing factors) scaled?

Answer 9

. Raw data converted to proportion or % mortalities

. Standardises data from different years (so you can compare)

Question 10

Why are k-values (killing factors) relative to the next stage?

Answer 10

. Assume mortality factors are sequential

Question 11

What are the uses of k-values (killing factors)?

Answer 11

. Can be summed to show overall mortality
. Compare k-values across a range of years to identify key factor
. Compare k-values with population size to identify regulating factor
(. Many insect examples but fewer mammal or bird examples)

Question 12

What are the two types of life tables that can be developed? What does it depend on?

Answer 12

. Static life tables
. Fixed life tables
Depends on how the survival is measured

Question 13

How are fixed cohort life tables survival measured? Give the positives and negatives of them compared to other life tables

Answer 13

Examine the population born in a particular year (cohort), through the death of every individual born in that year.
Most reliable data.
Major particle problems in construction- serious problem hindering their use

Question 14

How are static life tables survival measured? Give the positives of them over other life tables

Answer 14

The whole animal population is studied within a single year.
Easier to construct.
Confuses two processes:
- age-specific changes in birth and death rates
- year- to- year variations in these rates in the past
Nevertheless provide a useful overview
May be only solution where cohort life tables are impossible to construct

Question 15

Why are there two methods of constructing life tables (fixed or static)?

Answer 15

. Depends on the life-cycles of the animals involved
. Species with a simple annual life cycle- much easier to analyse as a cohort (e.g. many insects): fixed cohort life table
. Species which live for several years, especially birds and mammals, would need to mark it tag each individual (born in a year- difficult)
. This is often impractical, hence need to look at population segment: static cohort life table

Question 16

What do diagrammatic life tables provide?

Answer 16

A simple overview of births/ deaths/ survivorships

Question 17

Conventional (tabular) life tables are more complex than others, but provide more quantities and biologically meaningful information. What do they allow?

Answer 17

You to infer what’s going on in a population and determine the major detergents of population mortality and regulation. (Deeper understanding of the processes)