Data on red grouse ticks from Elston et al. 2001

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

Source

Robert Moss, via David Elston

Details

grouseticks_agg is just a brood-level aggregation of the data

References

Elston DA, Moss R, Boulinier T, Arrowsmith C, Lambin X (2001). “Analysis of aggregation, a worked example: numbers of ticks on red grouse chicks.” Parasitology, 122(5), 563–569. doi:10.1017/S0031182001007740 .

Examples

if (interactive()) {
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))
}