fishmethods (version 1.9-0)

lifetable: Life Table Construction

Description

Life tables are constructed from either numbers of individuals of a cohort alive at the start of an age interval (nx) or number of individuals of a cohort dying during the age interval (dx).

Usage

lifetable(age = NULL, numbers = NULL, r = NULL, type = 1)

Arguments

age

vector of age intervals (e.g., 0 to maximum cohort age).

numbers

number of individual alive (nx) or dead (dx)

r

known rate of increase (r) for methods 3 and 4

type

numeric value of method to use to calculate life table.

1 = Age at death recorded directly and no assumption made about population stability or stability of age structure - Method 1 in Krebs (1989). 2 = Cohort size recorded directly and and no assumption made about population stability or stability of age structure - Method 2 in Krebs (1989). 3 = Ages at death recorded for a population with stable age distribution and known rate of increase - Method 5 in Krebs (1989). 4 = Age distribution recorded for a population with a stable age distribution and known rate of increase - Method 6 in Krebs (1989).

Value

Details

Following Krebs (1989:413-420), standard life tables are calculated given age intervals and either cohort size or deaths. X=age interval, nx=number of individuals of a cohort alive at the start of age interval X, lx = proportion of individuals surviving at the start of age interval X, dx = number of individuals of a cohort dying during the age interval X, qx=finite rate of mortality during the age interval X to X+1, px=finite rate of survival during the age interval X to X+1, ex=mean expectation of life for individuals alive at start of age X. For method 5, dx is corrected for population growth by dx'=dx*exp(r*x) and in method 6, nx is corrected for the same by nx*e(r*x). See Krebs for formulae.

References

Krebs, C. J. 1989. Ecological Methodologies. Harper and Row, New York, NY. 654 p.

Examples

data(buffalo)
lifetable(age=buffalo$age,numbers=buffalo$nx,type=2)