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Hi everyone
I've been following this discussion on Rosellas
with a little interest. I'm certainly not trying to bite anyone's head off
here and I know that this is a bit of a can of worms and that this can has
been kicked plenty of times before, but I am surprised that so many
correspondents adhere to the old Biological Species Concept (BSC).This
conception, which broadly states that if an organism can breed with
another and the resultant offspring are viable then the organisms in
question are of the same species, is largely discredited nowadays. This
conception really doesn't work very well with most forms of life and certainly
doesn't work well with birds at all. Its weakness is definitely demonstrated
here in the case of Rosellas. Here, we have a number of very
unique types of birds in the Platycercus genus and yet
because many of them can breed with several others this old BSC
is used to mount an argument that this group be reduced to a few species
only. I can think of many reasons (both philosophical and practical)
why such a position is fraught with danger but it certainly fails
to adequately reflect the diversity of this assemblage of birds: ie. the
reality.
On the other hand, there is the Phylogenetic
Species Concept, which states that if a cohesive population of organisms
exhibits a distinct character or characters, then these can be considered to be
a "type", or "species". This conception deals with these issues far more
elegantly and in closer accord with our knowledge of genetics and cladistics.
The boundaries are frequently drawn within a narrow realm
of genetic variation so that we do not end up with "splitting" ad
infinitum. This is a concept which is not only satisfactory at all times (try
applying the BSC to many marine species!) but also reflects the diversity
of life more precisely. The most frequent argument I hear against this concept
is posed by folk who don't wish to have to deal with a greater variety of
species or two volume field guides. Unfortunately, we have to deal with the
reality of nature around us if we are to gain a more complete understanding of
it. This should not be held back simply because we might desire comfort and
familiarity in our recreational pursuit of bird watching.
I think that it can therefore be easily
resolved that each of these birds reflects the diverse genetic nature of the
Platycercus genus as each displays distinct characteristics. The Yellow Rosella,
Adelaide Rosella, Crimson Rosella, Green Rosella, Northern Rosella, Pale-headed
Rosella, Eastern Rosella and Western Rosella are each distinctive types of
Rosella and are therefore distinct species of Rosellas. That gives us eight
species.
Sorry if I've trodden on toes, but that's reality
as I see it (and as seen by many who are far more learned than yours
truly).
Happy birding
Ricki
Broome WA
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