Function to calculate the variance in size differences between adjacent, ordered species. If there is a tendency towards a constant absolute size difference between adjacent species, this variance will be relatively small. Alternatively, if some adjacent species are close in size, but others are very distant, this variance will be large. Small variances might be indicative of assemblages in which there is a competitively-based limit to similarity.
a vector of non-negative trait measures, one for each species
Returns the variance of the absolute difference between adjacent, ordered values.
Poole, R.W. and B.J. Rathcke. 1979. Regularity, randomness, and aggregation in flowering phenologies. Science 203:470-471.
Simberloff, D. and W.J. Boecklen. 1981. Santa Rosalia reconsidered: size ratios and competition. Evolution 35: 1206-1228.