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A survivorship curve is a graph showing the number or proportion of individuals surviving to each age for a given species or group (e.g. males or females). Survivorship curves can be constructed for a given cohort (a group of individuals of roughly the same age) based on a life table. A survivorship curve is a graph showing the number or proportion of individuals surviving to each age for a given species or group (e.g. males or females). Survivorship curves can be constructed for a given cohort (a group of individuals of roughly the same age) based on a life table. There are three generalized types of survivorship curves: The number or proportion of organisms surviving to any age is plotted on the y-axis (generally with a logarithmic scale starting with 1000 individuals), while their age (often as a proportion of maximum life span) is plotted on the x-axis. In mathematical statistics, the survival function is one specific form of survivorship curve and plays a basic part in survival analysis. There are various reasons that a species exhibits their particular survivorship curve, but one contributor can be environmental factors that decrease survival. For example, an outside element that is nondiscriminatory in the ages that it affects (of a particular species) is likely to yield a Type II survivorship curve, in which the young and old are equally likely to be affected. On the other hand, an outside element that preferentially reduces the survival of young individuals is likely to yield a Type III curve. Finally, if an outside element only reduces the survival of organisms later in life, this is likely to yield a Type I curve.

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