Things are never simple in biology, which causes a lot of trouble to the rational minds of men.
4 thoughts.
(1) In addition to Mario's excellent gemonensis example, I think we need to be careful about our faith in external features, especially colouration of closely related species with a lot of variability. This might cause overlap and/or parallelism in phenotypic expression, right? As I already said to Ilias off the forum, I believe we should in some cases accept that we cannot attribute every animal to a species, especially since the molecular revolution. If you don't buy this, let me know when you're ready for your blind test on Speleomantes
![Wink ;)](./images/smilies/icon_e_wink.gif)
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(2) Whether species colonise an island and/or persist, is a process which involves chance. Either or both can - accidently - reach an island directly or indirectly at different moments in time. If they are indeed two valid species, competitive exclusion is likely to result in one of both remaining as a result of niche similarity (with Kos being the exception, if indeed both species live there). For me, this, by itself, can be enough reason to explain island distributions that don't really cluster like you would expect or (worse) like.
(3) A role is certainly played by sea trenches as a proxy for past biogeographical barriers. There are parts of the sea between Karpathos and Rhodos, as well as between Karpathos and Crete, which are over 1000m in depth. While this will not explain the entire observed distribution of the two species by itself, it might explain the Karpathos case as the result of an old colonisation followed by.
(4) Maybe someone will come up with some evidence that there's no reproductive isolation between both taxa and lump them back into a single species?
( I don't know the original species split evidence by heart. Mario, would that be Schätti & Wilson 1986? Or Schätti 1988? )
I'm sure this is all stuff you all already know, but indulge me for sorting out my thoughts in public
![Mr. Green :mrgreen:](./images/smilies/icon_mrgreen.gif)