number of lions in european zoos

[Giant Panda]

A subspecies is no more artificial than the concept of species, or indeed any biological taxonomy. Any problem with subspecies definitions exists in species too, and vice versa.

Using the biological species concept, subspecies always:

1. Differ in appearances – even if it may be internal, e.g. cranial measurements.
2. Differ in genetics – but not enough to prevent complete hybridization events.
3. Differ in distribution – subspecies can never be sympatric. They can, however, be parapatric, but without an ecological border this will generally result in a cline (itself invalidating the subspecies).

If you remove *any* of these, the subspecies is invalid. There are obviously plenty of questionable subspecies (and species), but this is strictly because only a minority of species have had a modern, taxonomic review. None of these fully resolve the potential problems with clines, hybrid zones, ring species, genetic drift, polyphyletic/paraphyletic species (as exist under the biological species concept) and "super hybrid" groups (e.g., Anseriformes), but those present equal problems to species vs. subspecies.

In some fields, the phylogentic species concept is used with an increasing frequency and (in its strict form) this invalidates subspecies entirely. Any valid subspecies automatically becomes a species.

NB. Old habits die hard and I've not really managed to make the shift myself, but ICZN rules now stipulate that nominotypical should be used for the type subspecies.

Again, that depends on your definitions. As I’m sure you’re aware, three-dozen different species concepts have been proposed in the literature and, as I said in my previous post, the species classification is also an artificial one *to an extent*. However, I tend to follow Darwin on this point: every biologist agrees on what constitutes a species in most cases.

That’s not the case with subspecies where, as you point out, most fail to meet your criteria. Not to mention, those criteria are extremely broad. Most populations have a unique genetic signature ("differ in genetics"), but that doesn't make them different subspecies. As for the difference in "appearance", there's no clear distinction between what constitutes subspecies-level morphological differences (even species-level) and what doesn't. Phenotypic plasticity further complicates the issue, whilst preserving genetic diversity even without morphological divergence is important.

The BSC has many well-known flaws (especially outside higher verts), but is a good example of where defining a species is not artificial, whereas defining a subspecies is. I also prefer it to the PSC, which is fundamentally artificial. That is, the requisite degree of differentiation for populations to be considered separate species is necessarily arbitrary.

Hence why I tend to think in terms of ESUs: which populations should have their genetic integrity preserved (maintaining diversity at the species level) and which should we interbreed (increasing diversity at the individual level)? This is a practical definition, but relevant from a conservation standpoint.