Definition of Survivorship curve:
A survivorship curve is a graph showing the number or proportion of individuals surviving to each age for a given species or group
For making survivorship curves, ecologists identify a cohort, which is a group of individuals of the same species, in the same population, born at the same time.
It provides information regarding different population parameters like lifespan, survival rate, mortality rate of a particular population of a species.
Population ecologists have classified 3 types of Survivorship curves Type I, Type II and Type III.
Type I (Convex curve)
- Late loss, high mortality rate after reaching old agae
- High survivorship throughout life till old age sets in
- Majority reaches maturity
- Typical of k selected species with very few offspring’s. See r-selected vs k selected species
Eg: Elephants, Humans, annual plants
- Constant loss or death rate independent of lifespan
- Independent of age
Eg: Birds, rodents, Hydra, perennial plants
Type III (Concave curve)
- Early loss, high mortality during younger age
- Low mortality after maturity,
- Typical of r -selected species with numerous offspring’s
Eg: Oysters, Small fishes, trees, Insects