Survivorship is the probability that individuals from the original cohort (age 0) get to a certain age (age x). Survivorship up to the start of March is 0.8.
<h3>
What is a life table?</h3>
It is a representation of life and death patterns in a cohort. It includes the probability for different organisms in the population to live, survive, reproduce or die.
It is composed of information provided by parameters like age structure, natality rate, and death rate per age concerning the whole population.
There are two types of life tables:
- Horizontal life table
- Vertical life table
<h3>What is the horizontal life table?</h3>
This is a representation of a cohort destiny, from the born moment to the death moment of all individuals, including survival and fecundity per age.
A cohort is a group of individuals of the same age that are incorporated into the population at the same time.
This table is based on different vital statistics. Among them, we can mention,
- Number of individuals registered at a certain age, N(x)
- Number of individuals at initial age (recent born, seeds, propagule), N(0)
- Specific survivorship per age, l(x)
- Transition rate from one age to the next one, p(x)
- The proportion of the original cohort that dies during a certain age x, d(x)
- Specific mortality per age, q(x)
Specific survivorship per age, l(x), is the proportion of individuals from the original cohort that gets to survive reaching a certain age. It is the probability that a recent born gets to a certain age.
l(x) = N(x) / N(0)
Values must go from <u>0 to 1</u>. By definition, when l(x) = 1, then X = 0
In the exposed example, we know that
- N(0) = 200 rats ⇒ new borns
- N(x) = 160 rats ⇒ three months individuals
l(x) = N(x) / N(0)
l(x) = 160 / 200 = 0.8
Survivorship specific per age up to the start of March is<u> 0.8 = 80%</u>
You can learn more about life tables at
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