Survivorship curves [3 types]

Survivorship curves are the graphical representation of the number of individuals alive in a population at various ages. These curves are graphs that show what fraction of a population survives from one age to the next. Population rate depends on many factors like- mortality, natality, immigration, emigration etc.

Types of Survivorship curves:

These curves are of three general types: 1) Type 1 survivorship curve (highly convex curve), 2) Type 2 survivorship curve (diagonal curve), 3) Type 3 survivorship curve (highly concave curve),

Type 1 survivorship curve: (Highly convex curve)

1. Rate of loss for juveniles is relatively low (high survival at early age).
2. High age-specific survival probability in early age and middle life.
3. Most individuals are lost later in life, as they become older and more prone to sickness and predators (mortality high at later age).
4. Have relatively few offspring but invest much time and resources in raising their young. High parental care.
5. Many large mammals including humans, exhibit type I curves.
6. Species are iteroparous (organism breed several times during the course of their life span).
7. Examples: Humans and large animals like deer, sheep, mango tree etc.

Type 2 survivorship curve: (Diagonal curve)

1. This is an intermediate between Types 1 and 3 curves.
2. Individuals die at a constant rate.
3. Roughly constant mortality probability is experienced regardless of age.
4. Examples: Small mammals, song birds, reptiles, American robin, lizards, mice, rodents and some annual plants.

Type 3 survivorship curve: (Highly concave curve)

1. Most of the Juveniles die or are eaten, but a few reach a favorable habitat and thrive.
2. Rate of loss for juveniles is relatively high (high mortality/death rate at early age).
3. These curve flattens out for those organisms that have avoided early death (decreased mortality low at later age)
4. Have relatively high numbers of offspring but invest no time and resources in raising their young. (low/no parental care).
5. Many fish and marine invertebrates fit this pattern.
6. These organisms breed once during their lifetime and termed as semelparous.
7. Examples: Barnacles, many trees, frogs, and insects, oysters etc.

Diagram of three types of survivorship curve:

Other related notes:

1. Lotka-Volterra model: https://thebiologyislove.com/lotka-volterra-model/
2. Population growth- Exponential growth: https://thebiologyislove.com/population-growth-exponential-growth/
3. Population growth- Geometrical growth: https://thebiologyislove.com/population-growth-geometric-growth/

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