two.samp.cir: Computes analytical abundance estimates for two-sample...
In DistanceDevelopment/WiSP: Wildlife Simulation Package (wisp)

Description Usage Arguments Details Value Warning Note Author(s) References See Also Examples

Performs sex-specific harvest of animals from a simulated population, and produces analytical estimates of abundance and standard error for two-occasion change-in-ratio estimator.

1	two.samp.cir(rm.pop, frac.prehunt, frac.posthunt, frac.harv.male, frac.harv.fem)

`rm.pop`	Population object being harvested and sampled (likely created by `make.twosex.pop`)
`frac.prehunt`	Proportion of the population sampled prior to the harvest
`frac.posthunt`	Proportion of the population sampled after to the harvest
`frac.harv.male`	Proportion of males in the population removed during harvest
`frac.harv.fem`	Proportion of females in the population removed during harvest

This function augments the WiSP package by performing type-specific (think about type as equivalent to gender) harvest (or removal). The sampling process of a change-in-ratio study is to a) sample the population prior to the harvest to estimate sex ratio, b) harvest population in a sex specific manner, and c) sample population after harvest to again estimate sex ratio.

`point.cir`	Estimated point estimate of abundance
`se.cir`	Standard error of abundance estimate
`coef.var`	Coefficient of variation of estimate (not percentage)

It is not impossible for the point estimate of abundance to be negative; particularly when the difference in harvest between males and females is small. This is a nonsensical result, and hence, the estimate is not considered admissable. In this situation, all values returned by this function are set equal to NA.

Specifically, eqn. 5.15 of Borchers et al. (2002) is used for the point estimate, and 5.17 for the variance estimate. This function constitutes a building block of sim.cir.2 and its relative sim.cir.2.summary, in that repeated calls to two.samp.cir are made by these other functions to generate replicate realizations of an experiment.

Eric Rexstad, RUWPA ericr@mcs.st-and.ac.uk

Borchers, Buckland, and Zucchini (2002), Estimating animal abundance: closed populations. Chapter 5 http://www.ruwpa.st-and.ac.uk/estimating.abundance

two.samp.cir, sim.cir.2, make.twosex.pop

library(wisp)
example.popn <- make.twosex.pop(abund=200, prop.male=0.4)
single.example.result <- two.samp.cir(rm.pop=example.popn, frac.prehunt=0.2, frac.posthunt=0.4,
                         frac.harv.male=0.6, frac.harv.fem=0.02)
single.example.result