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

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, 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

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))
}