AASAGACITY.NET
  Knowledge is Empowering
A scoring system to define a species; an evaluation of a taxon/some taxa, using the Sensible Species Definition. 5 points between taxa makes a different species.



Geographic separation/Chance
of cross-breeding
Morphological and plumage differences Voice

Song/Calls

Habitat preference
Behaviour
including
migration
Known
DNA differences

Total Points
sp
or
subsp

Scoring 0-1-2-3 0-1-2-3 0-1-2-3 0-2-3-4 0-1-2-3 0-2-4-5

A SENSIBLE SPECIES DEFINITION (Anderson 1998 and 2012)
Species are populations that are interbreeding and which are reproductively isolated from other such populations by their reproductive isolating mechanisms.
These may include -
     geographic separation / chance of cross-breeding;
    morphological and plumage differences;
    voice;
    habitat preference;
    behavioural differences such as nest-building, social grouping or migration;
    consistent DNA differences.
Each mechanisms can be weighted according to the strength of difference from a recognised species and given a score between 0 and 5; a total of 5 would give the taxon species status.
0





1






2





3




4





5




Broad hybrid zone





e.g. Narrow and stable hybrid zone,
or good chance of interbreeding.



e.g A small chance of interbreeding.



No chance of interbreeding.

Feather tracts and/or bare parts a little different,



Feather tracts and/or bare parts noticeably different,


Feather tracts and/or bare
parts very different.

Feather tracts and/or bare
parts completely different.
Not so different voice range and/or song phrases.





Noticeably different voice range and/or song phrases,





Completely different voice range and/or song phrases.
Similar or slightly different habitat preferences.








Noticeably different habitats.







Completely different habitats.
Slightly different behaviour.





Noticeably different behaviour.




Very different behaviour.
DNA differences are barely measurable.




DNA differences are measurable.



DNA differences are larger.



DNA differences are large enough to probably have non-viable offspring.




DNA differences are so great that viable inter-breeding would be impossible.




Black-fronted White-eye  Zosterops atrifons 
Comparison of a Universally Accepted Species with Other Taxon such as a Subspecies
 Geographic separation/Chance
of cross-breeding
Morphological and plumage differences
Voice
Song/Calls

Habitat preference

Behaviour
differences

DNA differences

Total Points
sp
or
subsp
Research -
Zosterops a. atrifrons      
Black-fronted White-eye
Zosterops a. nehrkorni          Sangihe White-eye
Zosterops a. sulaensis           Sula White-eye
Zosterops a. stalkeri              Seram White-eye
Zosterops a. minor            N.G. Black-fronted White-eye
Zosterops a. somadikartai           Togian White-eye
Discussion -
Zosterops atrifrons, first described by Alfred Wallace in 1864, was/is a species which extends 2700 km eastwards from Sulawesi, through the  Moluccas and New Guinea, to the Bismarcks. These days some regard it as a superspecies, i.e. a taxon comprising several species.
As in such wide ranging species many differences in plumage and voice occur along the chain of distribution. With the subspecies of Zosterops  atrifrons on mainland New Guinea and island blocks to the west, as listed above, the plumage differences are not particularly large, plus they can sometimes be seen to grade into one another.
An example of this is given in "The Birds of New Guinea and the Bismarck Archipelago", Coates & Peckover 2001, under the page heading -
       BLACK-FRONTED WHITE-EYE  Zosterops atrifons
"Forehead and forecrown either yellow-green like (the) back (race minor of Yapen Is & North, east to Adelbert Mts) or black (rest of NG, intergrading with minor in Vogelkop region); - -. ".

As with the plumage, voice differences along a species distribution often form a gradient and, in the case of  although not greatly studied, may do the same.

Conclusions -

Although the 5th edition of "Birds of the World: A Checklist", Clements 2000, shows Zosterops minor, Black-fronted White-eye, as split from Zosterops atrifrons by then, as late as 2001 Coates & Peckover still regarded it as a subspecies; there seems little evidence that that should have ever changed.  

0
2
1
2
2
1





0
0
0
0
0
0


0
1
1
1
1
1





0
0
0
0
0
0









0
0
0
0
0
0








0
0
0
0
0
0








0
3
2
3
3
2








sp
subsp
subsp
subsp
subsp
subsp