```
#' Plot residuals of dewlap color
#'
#' This function plots the residuals of a set of dependent variables across islands and habitats. Residuals are taken as the deviation from the group mean. Residuals are plotted against group means (fitted values).
#'
#' @param specdata A data frame containing at least columns for the dependent variables, as well as a column "island" and a column "habitat".
#' @param vars A character or integer vector. The names, or indices, of the dependent variables in \code{specdata}.
#' @return Nothing. Just one (or more) scatter plot(s).
#' @author Raphael Scherrer
#' @export
# Function to plot residuals of a two-way ANOVA (simple regression)
plot_residuals <- function(specdata, vars) {
residuals <- sapply(vars, function(curr.variable) {
specdata$X <- specdata[,curr.variable]
# Fit a linear model
mod <- lm(X ~ island*habitat, data = specdata)
# Check the residuals
par(mfrow = c(2,2))
plot(mod, main = curr.variable)
par(mfrow = c(1,1))
return(resid(mod))
})
return(residuals)
}
```

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