flatlizards {BradleyTerry}R Documentation

Augrabies Male Flat Lizards: Contest Results and Predictor Variables

Description

Data collected at Augrabies Falls National Park (South Africa) in September-October 2002, on the contest performance and background attributes of 77 male flat lizards (Platysaurus broadleyi). The results of exactly 100 contests were recorded, along with various measurements made on each lizard. Full details of the study are in Whiting et al. (2006).

Usage

data(flatlizards)

Format

This dataset is a list containing two data frames: flatlizards$contests and flatlizards$predictors.

The flatlizards$contests data frame has 100 observations on the following 2 variables:

winner
a factor with 77 levels lizard003 ... lizard189
loser
a factor with the same 77 levels lizard003 ... lizard189

The flatlizards$predictors data frame has 77 observations (one for each of the 77 lizards) on the following 18 variables:

id
an integer identifier for each lizard
throat.PC1
numeric, the first principal component of the throat spectrum
throat.PC2
numeric, the second principal component of the throat spectrum
throat.PC3
numeric, the third principal component of the throat spectrum
frontleg.PC1
numeric, the first principal component of the front-leg spectrum
frontleg.PC2
numeric, the second principal component of the front-leg spectrum
frontleg.PC3
numeric, the third principal component of the front-leg spectrum
badge.PC1
numeric, the first principal component of the ventral colour patch spectrum
badge.PC2
numeric, the second principal component of the ventral colour patch spectrum
badge.PC3
numeric, the third principal component of the ventral colour patch spectrum
badge.size
numeric, a measure of the area of the ventral colour patch
testosterone
numeric, a measure of blood testosterone concentration
SVL
numeric, the snout-vent length of the lizard
head.length
numeric, head length
head.width
numeric, head width
head.height
numeric, head height
condition
numeric, a measure of body condition
repro.tactic
a factor indicating reproductive tactic; levels are resident and floater

Details

There were no duplicate contests (no pair of lizards was seen fighting more than once), and there were no tied contests (the result of each contest was clear).

The variables head.length, head.width, head.height and condition were all computed as residuals (of directly measured head length, head width, head height and body mass index, respectively) from simple least-squares regressions on SVL.

Values of some predictors are missing (NA) for some lizards, `at random', because of instrument problems unconnected with the value of the measurement being made.

Source

The data were collected by Dr Martin Whiting, University of the Witwatersrand, http://web.wits.ac.za/Academic/Science/APES/Research/MWLab/People/, and they appear here with his kind permission.

References

Whiting, M.J., Stuart-Fox, D.M., O'Connor, D., Firth, D., Bennett, N.C. and Blomberg, S.P. (2006). Ultraviolet signals ultra-aggression in a lizard. Animal Behaviour 72, 353-363. (http://dx.doi.org/10.1016/j.anbehav.2005.10.018)

Examples

library(BradleyTerry)
data(flatlizards)
##
##  Fit the standard Bradley-Terry model, using the bias-reduced
##  maximum likelihood method:
##
BTmodel <- BTm(flatlizards$contests ~ .., br = TRUE)
summary(BTmodel)
##
##  That's fairly useless, though, because of the rather small
##  amount of data on each lizard.  And really the scientific
##  interest is not in the abilities of these particular 77
##  lizards, but in the relationship between ability and the
##  measured predictor variables.
##
##  So next fit (by maximum likelihood) a "structured" B-T model in
##  which abilities are determined by a linear predictor.  This 
##  reproduces results reported in Table 1 of Whiting et al. (2006).
##
BTmodel2 <- BTm(flatlizards$contests ~ throat.PC1 + throat.PC3 +
  head.length + SVL, data = flatlizards$predictors)
summary(BTmodel2)

[Package BradleyTerry version 0.8-7 Index]