Type III curves are typical of many aquatic animals and many invertebrates. In a population described by a Type I curve, most members of the population live out their species typical life span and die of old age. Typically, relatively few young are produced and each receives some parental care and has a relatively large chance of surviving to adulthood. Humans with access to modern health care have a Type I curve, although plots of actual life table data for humans always include the aforementioned first year dip, reflecting the great vulnerability of infants to disease and accidents. In populations described by a Type II curve, animals die at a constant rate, regardless of age.
Deaths typically occur as a result of accidents and disease, with relatively few from old age.
This reflects the vulnerability of small animals to many different types of environmental perturbations. In populations described by Type III curves, many animals dies very early in life. Later deaths occur at a constant, age-independent rate. Often many, many small young are produced, and they are given little or no care. Many invertebrate species are described by this type of curve, particularly aquatic invertebrates, but fishes also often follow this pattern.