Understanding Survivorship

Objectives

• To analyze mortality data and extract information to create survivorship curves.

• To compare and contrast male and female survivorship

• To evaluate data for validity and suggest improvements to data collection method

Introduction

Survivorship is based on density dependent/independent factors as well as other natural occurrences. However, rates are subject to changes based on the environment. Nonetheless, survivorship rates are fairly consistent and correspond to their respected curves. Ecologists classify these survivorship trends as Type I, Type II, and Type III.

Type 1: Human, dolphins, elephants: low mortality rate (early on) and give birth to few young. Parental care is high, rarely preyed on, and migration is low, thus, more likely to survive.

Type 2: Squirrel, cockroaches, fish and many plants: Mortality rate is common (linear), birth rate is medium to high, and migrate an average amount. Parental care is also not as long as Type 1 and Type 2s are more preyed on.

Type 3: Clam, lizards: Birth rate is extremely high and mortality rate is extremely high. There is little to usually no parental care.

Materials

We will need:

a cemetery (or access to cemetery records)

a calculator

a pencil or pen

paper

Procedure

Age-structure information about a population can be very helpful in analyzing its potential to persist and grow. By recording data on mortality rates for different age groups, it is possible to construct a survivorship curve for a population.

1. A cemetery was visited and data was collected from at least 100 different gravestones (find 50 males and 50 females). the gender and the age at death were noted.

Age Number of males that died at this age Number of females that die...

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... drastically different in different environments; this metric is not usually considered to be a property of a species. Besides the constraint of the general life history strategy of a species, the shape of survivorship curves can be affected by both biotic and abiotic factors, such as competition and temperature.

The factors that might affect their accuracy are: sample size, country, random observations etc.

Q3. What type of survivorship do your curves show? Is this what you expected?

Type I survivorship is shown by the curves plotted. Yes, this is what I expected.

Q4. How do you think the data would change if we focused on individuals born now and followed their survivorship patterns into the future?

The individuals born now are having better life- expectancy than earlier as there are better medical facilities available.