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Life tables Were first used to estimate insurance risk in human populations –Divides the population into age specific classes –Estimates the age-specific.

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Presentation on theme: "Life tables Were first used to estimate insurance risk in human populations –Divides the population into age specific classes –Estimates the age-specific."— Presentation transcript:

1 Life tables Were first used to estimate insurance risk in human populations –Divides the population into age specific classes –Estimates the age-specific mortality risk in each class

2 A life table for a town in the East Midlands agepopdeath% death1 death in <

3 Assembling a life table Cohort or Dynamic life table Assembled by following the fate of a cohort from birth to death. Static life table Assembled estimating the age specific death risks from the age structure at a given time

4 age survivorship lx estimated age1999survivorship lx Dynamic life table Static life table

5 estimated age1999 original population survivorship lxsurvivorship estimated age1999survivorship lx However a static life table assumes the population is stable which is usually not true Original estimates But what if the population is decreasing? Decreasing population

6 estimated age1999 original population survivorship lxsurvivorship Population increasing

7 Phlox drummondii (annual phlox) is native to central and eastern Texas. It is a winter annual and grows abundantly in sandy fields and on roadside verges. It germinates in response to cool rainy weather.

8 q x =l x -l x+1 the proportion of individuals that have died over a time period = the mortality rate.

9 time days Average mortality rate per day time days Average mortality rate per day Log scale Mortality analysis

10 Where b x seed =number of seed per plant (B x /N x )

11 Fecundity analysis time days Number of seed produced per plant

12 Diagrammatic dynamic life table for Phlox drummondii Rectangles=stages in the life-cycle Inverted triangles= transition probabilities Diamond=seed production

13 A more complex diagrammatic life table of the biennial ragwort Senecio jacobea Biennial lives for 2 years reproducing at the end of the second year immigration Seed bank dynamics Dispersal germination establishment

14 Survivorship curves Type I = Found where there are ample resources e.g. human population in developed countries Type II = A constant risk of death throughout lifespan e.g. seeds in a buried seedbank Type III = High early mortality e.g. many plants reproducing by seed

15 Survivorship curve for Phlox drummondii

16 Survivorship curves of Erophila verna at different densities a=1-2 b=5-10 c=15-20 d=35-50 e=> s m -2 Survivorship curves for a species depend on a range of conditions

17 juveniles immature vegetative generative dead In plants stage of development can be a more useful definition of progress than age. Data are for a perennial Ranunculus acris


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