Some of the best examples of speciation are examples of diversification on archipelagos. These provide clear contexts of allopatry and hence provide the extrinsic barrier to gene exchange from the source usually mainland population. The most famous are the Galapagos Islands. This isolation and context of primary succession e.
"Same same but different": replicated ecological speciation at White Sands
Ecological speciation - Wikipedia
Metrics details. Our understanding of the geography of speciation is quite clear. The process involves the separation of a once-continuous range into two or more geographically isolated, or allopatric parts, which over time accrue genetic changes that result in new daughter species. Current distributions show that recently evolved species are currently allopatric, supporting the role of allopatry in speciation. However, many species originated in the early- to mid-Pleistocene, meaning that they persisted through the environmental perturbations of multiple glacial cycles. It has been assumed that species maintained allopatric distributions during these episodes of glacial advance and retreat. I used Grinnelian niche models to estimate species distributions at the Last Glacial Maximum and the Last Interglacial.
Of “Host Forms” and Host Races: Terminological Issues in Ecological Speciation
Sadedin and J. Hollander and M. Panova and K.
Daniel J. Successful communication and accurate inferences in science depend on the common understanding and consistent usage of the terms we apply to concepts of interest. Likewise, new terminology is required when important concepts have gone unnamed.