While discussing species distribution patterns along spatial, temporal or functional gradients one often finds a hump shaped species richness pattern. This is well documented in many taxa and spatial scales and known as the mid-domain-effect (e.g. Colwell & Lees 2000 ).
These patterns also arise stochastically (depending on the species range frequency distribution). So random distribution of species ranges midpoints are used as null models to test for these mid-domain-effects.
However, these models assume unfragmented species ranges. With a highly fragmented species range the pattern would look quite dissimilar.
So I don't want to start a discussion on the validity of this concept but rather ask:
Given a gradient and known species occurences on that gradient. Has anyone read an article about (or has an idea) what would be a good/unbiased* estimator for species range fragmentation?
*e.g: One that doesn't over- or underestimate fragmentation for rare or abundant species