According to present-day concepts of variation and speciation, Andersen's criteria are artificial.
Additional remarks on the distribution of this species are in the section on Zoogeography and Speciation.
In fact, isolation is a most important factor in speciation of insular populations (Baker, 1951:55).
Natural selection plus geographical and ecological isolation has undoubtedly been operative in speciation and in subspeciation.
The process of speciation within insular populations has been discussed by many authors.
Isolation of small populations is probably the most influential factor in the process of speciation in insular organisms.