The example reproduces data published in Kahilainen & Lehtonen (2001) on prey lengths from a sample of 59 individuals of stocked (S) and native (N) brown trout (Salmo trutta) in the subarctic Lake Muddusjarvi in northern Finland.
Column names refer to:
- FishID: a unique identifier for each individual fish within the geographic area;
- Type: stocked (S) and native (N) brown trout.
All other columns are lengths (in mm) of fish prey found in stomachs.
Kahilainen, K. and Lehtonen, H. 2001. Resource use of native and stocked brown trout Salmo trutta L., in a subarctic lake. Fisheries Management and Ecology 8: 83-94.
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# Summary of total length of preys in stomach content # by geographic region data(Trout) # Mean prey length by individual # First change zeros to NA troutTMP = Trout troutTMP[ troutTMP == 0] = NA individuals = by(troutTMP[, 3:7], troutTMP[, 2], rowMeans, na.rm=TRUE) TroutN = subset(Trout, Type == "N", PL1:PL5) TroutN = TroutN[TroutN > 0] TroutS = subset(Trout, Type == "S", PL1:PL5) TroutS = TroutN[TroutS > 0] boxplot(c(TroutS, TroutN) ~ c(rep("N", length(TroutN)), rep("S", length(TroutS)))) rm(list=ls(all=TRUE))