Survivorship curves

 Survivorship curves are a common tool used by population ecologists to understand how populations of organisms change over time. These curves graph the number of individuals surviving at different age intervals or life stages, typically from birth to death, and can be used to infer patterns of mortality and life expectancy within a population.

There are three main types of survivorship curves: Type I, Type II, and Type III, which differ in their shape and the age at which mortality rates increase.

• Type I survivorship curves are characterized by high survivorship rates early in life, followed by a rapid decline in survivorship as individuals approach old age. This pattern is often seen in large mammals and other long-lived organisms with low infant mortality rates.

  
  

• Type II survivorship curves show a roughly constant rate of survivorship across all age intervals. This pattern is seen in some birds, reptiles, and invertebrates.

  
  

• Type III survivorship curves are characterized by low survivorship rates early in life, followed by a period of high survivorship in adulthood. This pattern is often seen in species that produce many offspring with little parental investment, such as insects and some fish.

By examining the survivorship curve of a population, ecologists can gain insights into factors that affect population growth and survival, such as predation, disease, and environmental conditions.