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Frequently Asked Questions
Black Currawong

What is a "Species" and a "Sub-species"?

A very good question! We all think we know what a species is - and a Magpie is certainly not the same "type" of bird as a Galah - but if you look closely at magpies across the country you will see they vary - so are they all the same "species" or not? The answer is not clear. Going back to Magpies - whilst the markings do vary across the country, different populations interbreed where they meet and it is generally accepted that all Magpies are the same species.

Once upon a time scientists used the appearance of a species to classify it, and places similar looking birds in the same family. As time went on it became obvious that this was not a very good reflection of reality, and the Biological Species Concept (BSC) came into vogue. This concept, 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. Some of the issues are that it doesn't work at all for species that are a-sexual. It is hard to apply where populations are separated by physical barriers. And it also cannot be applied to extinct species. Finally there are instances of what are clearly separate "species" occasionally inter-breeding.

The Phylogenetic Species Concept (or PSC), states that if a cohesive population of organisms exhibits a distinct character or characters, then these can be considered to be a "species". This concept deals with these issues far more elegantly and in closer accord with our knowledge of genetics. It is unfortunately not always clear where to draw the line in the grouping of characteristics - there is always some genetic variation within a population and PSC has to decide when this is small enough not to cause a split of the species. This concept is not without critics but solves many of the problems of the BSC. One outcome of the PSC is that it tends to see more "species" than does the BSC - a BSC view of the world sees 5 Rosella species in Australia, a PSC has 8.

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