Function to calculate the minimum absolute size difference between species within an assemblage.
a vector of non-negative trait measures, one for each species
Although this index is typically used to examine body size differences in an animal assemblage, it could be used for any morphological index, such as beak size, or for a phenological "trait", such as peak flowering time in a plant assemblage.
Returns the minimum difference between adjacent, ordered values.
Simberloff, D. and W.J. Boecklen. 1981. Santa Rosalia reconsidered: size ratios and competition. Evolution 35: 1206-1228.