What is the survivorship curve?

The survivorship curve is a graphical representation of the percentage of individuals who survive a particular period, grouped by age. 

The survivorship curve is typically used to compare the cumulative percentage of survivors at each age relative to their initial cohort or group.

 The most commonly used survivorship curve is the five-year survival curve, which plots the percentage of individuals who survive for an initial (e.g., 5-year) period along the vertical axis against age on the horizontal axis.

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What are the three types of survivorship curves?

1. Type 1 Survivorship Curve

It is a graph that graphically illustrates a population that grows to adulthood without experiencing a decline in size. After birth, mortality is low for a very long time. Because they receive a lot of parental care when they are young, members of this population typically have low mortality rates for juveniles and subadults.

It is used to study the survivorship of human populations that experience little to no mortality during childhood.

Species that fit a Type 1 Survivorship Curve include the following:

Bears

Elephants

Gorillas

Humans

2. Type 2 Survivorship Curve

It is a graph that graphically illustrates a population that does experience a decline in size after birth.

After birth, mortality is high for a very long time. This pattern of low survivorship for juveniles and subadults and high survivorship for adults repeats through the adult life span until the population reaches its final size at death.

It is used to study the survivorship of human populations that experience high mortality rates during childhood.

Species that fit a Type 2 Survivorship Curve include the following:

There are examples of birds, mice, and other creatures with constant death or survival rates throughout their lifespans.

3. Type 3 Survivorship Curve

It is a graph that graphically illustrates a population that experiences an initial decline in size, followed by an increase in size (growth), then another decline to extinction.

Types 3 survivorship curves are used to study the survivorship of human populations that experience high mortality rates during childhood.

Species that fit a Type 3 Survivorship Curve include the following:

marine invertebrates, most fish, Trees

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Explain each curve with the characteristics of each survivorship curve

1. Type 1 Curve:

The low mortality rate for juveniles and subadults high mortality rate for adults.

2. Type 2 Curve:

The high mortality rate for juveniles, the low mortality rate for the rest of the life span, and the high mortality rate for adults.

3. Type 3 Curve:

The low mortality rate for juveniles and subadults is a high mortality rate for adults.

Types of limiting factors that account for the survivorship curve

1. Natural Selection:

The high natural selection will lead to a greater number of adults than young, producing the survival curve.

2. Environmental Conditions:

If the environment harbors so much disease, is so polluted, or has such a high level of predation that adults have trouble surviving, the young will not be able to survive even if there are enough resources for all.

3. Human impacts:

Destruction of habitat is a leading cause of extinction. If a species’ habitat is destroyed, it cannot survive because they have nothing to live on. They will eventually die off, leaving no young to continue the population.

What are the benefits of survivorship curves?

1. It helps us to understand how a species lives and dies in nature.

2. The curve is a good tool to compare survival rates between populations across the globe.

3. Survivorship curves can be used to estimate natural death rates of animals and plants from existing data and therefore provide a reasonable estimate of the potential maximum population size for those organisms. 

4. Survivorship curves help us to determine how the population will change through time.

5. You can use survivorship curves to predict the number of young produced by each female and compare it with known data from other populations. 

6. It is also used for estimating the age structure of a population and its growth rate, which can provide a more robust estimate of population size compared with other methods, such as the extrapolation of census data or direct age determination using ring counts.

Explain how the survivorship types differ from each other

Type 1 has its highest mortality rate for adults, and Type 3 has its highest death rate for juveniles.

Type 2 falls in between, with a high mortality rate for juveniles and a low mortality rate for adults.

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