**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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