R/aphids.R

In ecostats: Code and Data Accompanying the Eco-Stats Text (Warton 2022)

#' Aphid data
#'
#' A study of the effects of bird exclusion on biological control of aphids in oat and wheat fields in 
#' Germany (Grass \emph{et al.} 2017). Many thanks to Ingo for providing the raw data.
#' In each of two fields (one of oats, one of wheat) there were eight plots, four with plastic netting 
#' to exclude birds, and four without. Aphid abundance was counted on seven different occasions over 
#' the first 38 weeks following netting. The expectation was that aphid numbers would decrease on bird 
#' exclusion, because an important food source to tree sparrows is aphid predators, hoverflies and 
#' ladybird beetles, so presence of birds may be limit the effectiveness of a biological control of aphids.
#'
#' @docType data
#'
#' @usage data(aphids)
#'
#' @format A list containing two dataframes, \code{oat} and \code{wheat}, depending on the crop. Each
#' dataframe contains:\describe{
#' \item{Plot}{The plot ID, a factor with eight levels}
#' \item{Treatment}{A factor indicating whether birds were excluded, \code{excluded} or \code{present}.}
#' \item{Time}{The number of days since netting was applied.}
#' \item{counts}{Aphid abundance (counts)}
#' \item{logcount}{log(y+1)-transformed aphid abundance}
#' }
#'
#' @keywords datasets
#'
#' @references Grass \emph{et al.} (2017) Insectivorous birds disrupt biological control of cereal aphids.
#' Ecology, \bold{98} 1583-90.
#'
#' @examples
#' data(aphids)
#' cols=c(rgb(1,0,0,alpha=0.5),rgb(0,0,1,alpha=0.5)) #transparent colours
#' with(aphids$oat, interaction.plot(Time,Plot,logcount,legend=FALSE,
#'                                col=cols[Treatment], lty=1, ylab="Counts [log(y+1) scale]",
#'                                xlab="Time (days since treatment)") )
#'                                legend("bottomleft",c("Excluded","Present"),col=cols,lty=1)
"aphids"