Metrics for quantifying the similarity among ecological niche models

modOverlap.R

# The modOverlap function calculates three metrics: 
# Shoener’s D for niche overlap
# Hellinger distance between probability distributions
# Warren's I similarity statistic
#
# This function is also found in the fuzzysim package
#
# From https://modtools.wordpress.com/2015/10/30/modoverlap/

modOverlap <- function (pred1, pred2, na.rm = TRUE) 
{
  p1 <- pred1/sum(pred1, na.rm = na.rm)
  p2 <- pred2/sum(pred2, na.rm = na.rm)
  SchoenerD <- 1 - 0.5 * sum(abs(p1 - p2), na.rm = na.rm)
  HellingerDist <- sqrt(sum((sqrt(p1) - sqrt(p2))^2, na.rm = na.rm))
  WarrenI <- 1 - ((HellingerDist^2)/2)
  list(SchoenerD = SchoenerD, WarrenI = WarrenI, HellingerDist = HellingerDist)
}