Life Table & Survivorship curves Prajwal.pptx

LIFE TABLE and SURVIVORSHIP CURVES

1. LIFE TABLES & SURVIVORSHIP CURVES WELCOME Student : Prajwal Gowda M.A Roll No : 12292 Course- incharge : Ph . D . : 1 st year Dr. S Rajna Course: Insect Ecology & Diversity Department of Entomology DIVISION OF ENTOMOLOGY ICAR-INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI - 110 012

2. Life Tables Lotka (1925) is considered as father of Life tables. Life table is a detailed census of a given population. It is sometimes described as biology of a particular population. Life table is summary of a group of population whose number starts life together Life table describes the mortality occurring in successive age intervals during the life cycle of insect species. The construction of life table are borrowed from demographical studies. The Life tables should be replicated spatially and temporally. Richards (1940) opined that there is a successive reduction in the population of insect throughout a generation . Richards (1961) in Annual Review of Entomology coined the word Budget for the Life table.

3. Life table is basically a study where observations are undertaken frequently In Life table studies the word cohort is used very frequently which refers to population born at the same time with a shared characteristics. Prerequisites for constructing of a Life table Adults : Longevity of adult, Fecundity of adult, pre ovipositional period, mating period, sex ratio, No. of eggs laid by female, pattern of egg laying Eggs : duration, percentage hatchability Larva : duration, No. of instars, duration of individual instar Pupa : pupal duration, site of pupation. Requirements of Life table Intensive studies are required for recording age specific survival of species Measurement of variables like weather factors, parasitism, predation should also be recorded.

4. Types of life tables Age Specific Life table Time Specific Life table Horizontal Life table Vertical Life table Constructed for those organisms which have short life span Constructed for long lived animals Ex: Annual plants / insects Ex: Herd of elephants because following cohort of such individuals from birth to death would take long time Interval of observation is not regular but decided by the stage present Certain fixed intervals are pre decided and observations are taken during the fixed intervals Called Horizontal life table as all the stages are closely observed moving horizontally along the life of an organism Life history is prerequisite The flow of life cycle is cut vertically and observations are noted in each of the stage Age determination is pre requisite The frequency of recording of data should be designed in such as way that no important event should be lost

5. Construction of Hypothetical Life Table x is Cohort l x - is the number surviving at the beginning of age class d x - is the number dying during the age interval x L x - is the average number surviving in age class L x = (l x ) (l x +1)/ 2 d x f – factors responsible for death of individuals in that age class T x - is the no. of units of life at a particular stage. It has no real biological meaning e x – is the expected life at a particular stage or amount of life left. e x = T x /l x q x = refers to mortality per age interval and is expressed usually as a rate per 1000 alive at the start of that individual. q x = 1000 x d x / l x

6. x l x d x L x d xf T x e x = T x /l x q x 1 1000 300 850 =(1000+700)/2 No hatching Sterility Parasitization or Unknown reasons 2180 2.180 300 2 700 200 600 1330 1.90 286 3 500 200 400 730 1.46 400 4 300 200 200 330 1.10 667 5 100 50 75 130 1.30 500 6 50 30 35 55 1.10 600 7 20 10 15 20 1.0 500 8 10 10 5 5 0.5 1000

7. Calculation of survival rate using life table data S x - is the survival rate with in the age mentioned S x = x (l x – d x )/ l x Adult l x – is the no. of moths emerged in the lab from pupa collected from field N 1 = No. of eggs at the beginning of cohort in the column l x N 2 = No. of eggs produced can be worked out by No. of eggs X average fecundity N 3 = females x 2 Trend Index I = N 2 /N 1 S G = Generation survival = N 3 /N 1 K= log 10 N.log 10 N s K= Difference between successive value for log l x -Hence it is a measure of killing power of a mortality factor N = No. of individuals before mortality occurs N s = No. of individuals surviving the mortality

8. Survivorship Curves The "survivorship curves" is the graphical representation of the fall off of numbers with time in a given age (lx), is plotted against the age "x". The cohort life table data can be used to draw the survivorship curves. The shapes of the curve describes the distribution of mortality with age. Survivorship curves shows the no. of individuals which survive per 1000 of population through each phase of life. If the percent of total lifespan of organism is taken along X-axis and no. of survivals on Y-axis resulting curve is known as Survivorship curve. There are two schools of thought regarding survivorship curves. Deevey (1947 & 50) According to him lx of life tables are converted to log values and based on which a graph should be drawn. He obtained three different types of curves. Slobodkin (1962) used original values to plot curves without log values and obtained four different types of curves.

9. Curves proposed by Deevey Highly Convex curve In this type of mortality rate will be low until the life span is completed, heavy maternal care is exhibited. Many species of large animals like man and small rotifers exhibit this type of curve. 2) Intermediate or diagnol type curve This is a theoretical curve.

10. It indicates a constant rate of mortality occuring at every age, Age specific survival. Examples are Hydra, Gulls, Birds exhibit this type of curve. This is further divided into a) S tair step survivorship curve In holometabolous insects survival rate differ in successive life history and as a result the curve becomes stair step type. According to it the initial and final steep in the curve represents egg and short lived adult stage where as two middle segments represents larval and pupal stages which exhibits less mortality.

11. b) Linear Eg : Birds, Hydra etc. c) Slightly Concave curve This curve is exhibited by those organisms where mortality is high in young stages later stages it more or less constant. Honey bees, Mice, rabbits exhibit display this type of curve.

12. 3) Highly Concave curve Animals which do not have mechanisms to protect their young ones exhibit this type of curve. Since the mortality is very high in the early stages of life of an organism. However such organisms compensate by laying numerous eggs. Eg : oyster, shellfishes, oaktree .

13. Curves proposed by Slobodkin Highly Convex curve Type 1 Type 2

14. Highly Concave curve Type 1 Type 2

15. Applications of Life table & Survivorship curves Identifies “weakest link” in population Relates birth/dates rates to each other which provides information about survival strategy Useful for modelling population dynamics Can be used with fecundity tables to estimate intrinsic rate of increase Biases/disadvantages Sample may not reflect age structure in the population Marked animals may die at different rates than unmarked O ther biases such as differential survival by sex, increased predation at certain age

16. References 1. Insect Ecology, Peter Price, 1997, III edn , John Wiley and Sons Newyork . 2. Insect Ecology, P W Price, R F Denno , M D Eubanks, D L Finke and I Kaplan, 2011, Cambridge University Press. 3. Fundamentals of Ecology, E. P. Odum and G. W. barret , Thomas brooks/Cole Publn .

17. Thank you