grouseticks {lme4} | R Documentation

## Data on red grouse ticks from Elston et al. 2001

### Description

Number of ticks on the heads of red grouse chicks sampled in the field (`grouseticks`) and an aggregated version (`grouseticks_agg`); see original source for more details

### Usage

    data(grouseticks)

### Format

`INDEX`

  (factor) chick number (observation level)

`TICKS`

  number of ticks sampled

`BROOD`

  (factor) brood number

`HEIGHT`

  height above sea level (meters)

`YEAR`

  year (-1900)

`LOCATION`

  (factor) geographic location code

`cHEIGHT`

  centered height, derived from `HEIGHT`

`meanTICKS`

  mean number of ticks by brood

`varTICKS`

  variance of number of ticks by brood

### Details

`grouseticks_agg` is just a brood-level aggregation of the data

### Source

Robert Moss, via David Elston

### References

Elston, D. A., R. Moss, T. Boulinier, C. Arrowsmith, and X. Lambin. 2001. "Analysis of Aggregation, a Worked Example: Numbers of Ticks on Red Grouse Chicks." Parasitology 122 (05): 563-569. doi:10.1017/S0031182001007740. http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=82701.

### Examples

    data(grouseticks)
    ## Figure 1a from Elston et al
    par(las=1,bty="l")
    tvec <- c(0,1,2,5,20,40,80)
    pvec <- c(4,1,3)
    with(grouseticks_agg,plot(1+meanTICKS~HEIGHT,
                      pch=pvec[factor(YEAR)],
                      log="y",axes=FALSE,
                      xlab="Altitude (m)",
                      ylab="Brood mean ticks"))
    axis(side=1)
    axis(side=2,at=tvec+1,label=tvec)
    box()
    abline(v=405,lty=2)
    ## Figure 1b
    with(grouseticks_agg,plot(varTICKS~meanTICKS,
                      pch=4,
                      xlab="Brood mean ticks",
                      ylab="Within-brood variance"))
    curve(1*x,from=0,to=70,add=TRUE)
    ## Model fitting
    form <- TICKS~YEAR+HEIGHT+(1|BROOD)+(1|INDEX)+(1|LOCATION)
    (full_mod1  <- glmer(form, family="poisson",data=grouseticks))

[Package lme4 version 1.1-12 Index]