B.Sc. Zoology Plotting & study of Survivorship curve from a hypothetical data set

 🔷 Survivorship curve:

Survivorship curve is a graphical representation of diminishment of a cohort through time.

🔷Type: Three primary types of survivorship curves are-

• Type I- Highly convex: Population mortality is low until the age of life span.
• Type-II-Highly concave: Population mortality is high during young stages.
• Type-III-Diagonal: Age specific constant survival.

Later, Sigmoid (mortality is high initially then slow & almost constant, looks like s-shaped) & Stair step curve (survival rate differs in successive life history stages) also included.

When data from n_x column of a life table is plotted with the time interval (X) on horizontal axis & number of survivors on the vertical axis, the resulting curve shows a survivorship curve.

Curve can be plotted on either in normal arithmetic scale or on logarithmic scale of 10(Log ₁₀ scale)

A semi logarithmic or logarithmic plot in the ordinate is used so that a straight line on such a graph indicates a constant rate with respect to the age. The line on logarithmic plot indicates a constant specific rate of survival & helps in the comparison of species of widely different life spans.

🔷Requirements:

• Supplied age specific data set of survivors
• Graph Paper

X	0	1	2	3	4	5
nx	530	159	80	45	20	05
log nx	2.7	2.2	1.9	1.6	1.3	0.7

🔷Survivorship curve on log scale: 

On a graph paper nx (log 10 scale) is plotted against time interval (X) & following graph is obtained.

🔷Observation: Almost a diagonal straight line is formed.

🔷Conclusion: This survivorship curve of Grey Squirrels (Sciurus sp) from a population in Pennsylvania concluded that those individuals have an approximately constant chance of survival throughout life span, because the rate of death is more or less constant.

🔷Survivorship curve on arithmetic scale: On a graph paper nx is plotted against time interval (X) & following graph is obtained. 

🔷Observation: The survivorship curve shows 'concave' type (Type-III). 

🔷Conclusion: Here, Population mortality is higher during initial & young stages then individuals are well protected on the favorable life span.

🛑 Life table study:https://biomassfootprints.blogspot.com/2025/07/study-of-life-table-and-survivorship.html

💹 SET-I :https://biomassfootprints.blogspot.com/2025/07/study-of-life-table-and-survivorship.html

💹 SET-II :https://biomassfootprints.blogspot.com/2025/07/study-of-life-table-and-survivorship_18.html