Rcapture (version 1.1)

duck: Open Population Data for Eider Ducks

Description

This data set contains open population capture history data for eider ducks.

Usage

data(duck)

source

Coulson, J. C. (1984). The population dynamics of the Eider Duck Somateria mollissima and evidence of extensive non breeding by adults ducks. Ibis, 126, 525--543.

Details

The data are extracted from a 25-year study by Coulson (1984). The capture periods are six consecutives years : years 19-24. This data set is analysed in Cormack (1989). This data set's format is the alternative one, i.e. each row represents an observed capture history followed by its frequency.

References

Baillargeon, S. and Rivest, L.P. (2007). Rcapture: Loglinear models for capture-recapture in R. Journal of Statistical Software, 19(5), http://www.jstatsoft.org/ Cormack, R. M. (1989). Log-linear models for capture-recapture. Biometrics, 45, 395--413.

Examples

data(duck)
op.m1<-openp(duck,dfreq=TRUE)
op.m1$model.fit
  # The pvalue of the goodness of fit test based on the deviance is
1-pchisq(op.m1$model.fit[1,1],df=49)
plot(op.m1)
  # The residual plot shows a large residual for the 13 individuals 
  # captured all the times. We redo the analysis without them.

keep2<-apply(histpos.t(6),1,sum)!=6
op.m2<-openp(duck,dfreq=TRUE,keep=keep2)
op.m2$model.fit
1-pchisq(op.m2$model.fit[1,1],df=48)
  # The fit is still not satisfactory.
plot(op.m2)
  # The residual plot has the convex shape characteristic of 
  # heterogeneity in the capture probabilities. We also remove the 
  # individuals caught at 5 periods out of 6.

keep3<-apply(histpos.t(6),1,sum)<5
op.m3<-openp(duck,dfreq=TRUE,keep=keep3)
op.m3$model.fit
1-pchisq(op.m3$model.fit[1,1],df=42)
  # The fit is better but there is still heterogeneity in the data. 

  # To investigate whether the capture probabilities are homogeneous, 
  # one can fit a model with equal capture probabilities.
op.m4<-openp(duck,dfreq=TRUE,m="ep",keep=keep3)
op.m4$model.fit
  # It gives a much larger deviance; this model is not considered anymore.

  # We now investigate models for the growth rate N[i+1]/N[i] of this 
  # population using the multivariate normal distribution for the 
  # abundance estimates. The growth rates and their standard errors are
growth<-op.m3$N[3:5]/op.m3$N[2:4]
partial<-matrix(c(-op.m3$N[3]/op.m3$N[2]^2,1/op.m3$N[2],0,0,0,
                  -op.m3$N[4]/op.m3$N[3]^2,1/op.m3$N[3],0,0,0,
		  -op.m3$N[5]/op.m3$N[4]^2,1/op.m3$N[4]),3,4,byrow=TRUE)
sig<-partial%*%op.m3$cov[9:12,9:12]%*%t(partial)
cbind(estimate=growth,stderr=sqrt(diag(sig)))
  # An estimate for the common growth rate is
siginv<-solve(sig)
growth.e<-t(rep(1,3))%*%siginv%*%growth/(t(rep(1,3))%*%siginv%*%rep(1,3))
se<-1/sqrt(t(rep(1,3))%*%siginv%*%rep(1,3))
cbind(estimate=growth.e,stderr=se)
  # A chi-square statistics for testing the equality of the growth rates 
  # and its pvalue
chisq2<-t(growth-growth.e*rep(1,3))%*%siginv%*%(growth-growth.e*rep(1,3))
c(chi2stat=chisq2,pvalue=1-pchisq(chisq2,df=2))
  # The hypothesis of a common growth rate is rejected