Dynamics of mortality. Survival curves
Survival curves are used to monitor the dynamics of mortality in different age groups.
Survival curves are a way to graphically represent the dependence of the proportion of surviving individuals on their age.
Survival curves are constructed from data on mortality in different age groups in the population.
There are three main types of survival curves.
Curve I type (Drosophila type) describes a situation when high mortality is observed in adulthood.
Example: the curves of the survival of large mammals and insects approach the curve of type I, which soon after emerging from the pupa leave offspring and die (fruit flies, mayflies, etc.) or whose larval stages pass under favorable slightly changing conditions: soil, wood, living organisms.
Curve II type (hydra type) is typical for organisms with uniform mortality at any age (on the graph this corresponds to a straight line).
Example: these types of curves are typical for fish, reptiles, birds, herbaceous perennial plants, etc., with the only proviso that the counting is from organisms that have already passed the most vulnerable stages of their development.
A type III curve (oyster type) is characteristic of organisms that mostly die at the initial stages of their life.
Example: oysters lead an attached lifestyle in an adult state, and their larva is planktonic. It is during this period that they are most vulnerable. Individuals that have successfully passed the larval stage have a greatly increased chance of survival. This type of survival curves is typical for many animals with high fertility and lack of care for offspring and for most plants (in trees, less than 1% of seedlings survive to maturity, in fish – 1–2% of fry, in insects – less than 0.5% of larvae ).
Realistic survival curves are a combination of these types.