Aphid data

A study of the effects of bird exclusion on biological control of aphids in oat and wheat fields in Germany (Grass 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.

Usage

data(aphids)

Format

A list containing two dataframes, oat and wheat, depending on the crop. Each dataframe contains:

Plot

The plot ID, a factor with eight levels

Treatment

A factor indicating whether birds were excluded, excluded or present.

Time

The number of days since netting was applied.

counts

Aphid abundance (counts)

logcount

log(y+1)-transformed aphid abundance

References

Grass et al. (2017) Insectivorous birds disrupt biological control of cereal aphids. Ecology, 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)