1: Life tables & pop. growth Flashcards
What is survivorship?
probability of survival up to a given age
Describe a survivorship curve
→ no. of individuals in a pop. that are expected to survive to any specific age (x) - lx
→ Plotting the log of this value. on the y axis against the age on the x-axis = a survivorship curve:
Start with the total number of individuals in the pop. at age 0
Always decreasing curve (though might sometimes be nearly flat)
Declines to 0 at high age when all individuals have died
Describe a Type I survivorship curve
tells us mortality increases with age, at young ages it doesn’t change much
e.g humans
Describe a type II survivorship curve
tells us mortality is the same in every life stage
e.g birds
Describe a type III survivorship curve
Highest mortality rate in early stages of life e.g trees
What does a life table summarise?
summarising births and deaths for organisms at different ages, show quantities like survivorship for diff age classes
What are the 2 types of life table?
Cohort life table
Period life table
Describe a cohort life table
represents age-specific rates over lifetime of a cohort of organisms born during a relatively short period of time e.g 1 year
Describe a period life table
represents age-specific rates during a specific time period of a certain pop. (meaning diff age groups were born at diff times)
What type of life table is usually used in ecology and what group do they include?
cohort tables (also known as generation life tables) and only include females
Describe the values in a cohort life table
Survivorship (lx) = survival from age 0 to age x
Survival (Sx) = survival from age x to age x+1 (annual measure)
Fertility (mx) = mean no. of offspring produced by each individual surviving from age x-1 to age x
Give an example of what we can calculate using a cohort life table
Net reproductive rate
Annual growth rate
What is Net reproductive rate?
Represented by R0 (R number)
→ average number of female offspring produced by one individual female over her lifetime (birth to death)
- 2 useful interpretations:
A measure of per-gen pop. growth rate
A measure of fitness (lifetime reproductive success)
- Can also use to study infectious disease epidemics, parasite fitness
If R0 < 1, what happens to the population?
If R0 less than 1 = Pop. declines
If R0 > 1, what happens to the population?
If R0 greater than 1 = pop. increases
