Species explained please

[Tinkerbell]

Can anyone explain in simple terms why something is classed as belonging to one species and not another? Some bird types may be fairly obvious, but why for example is one orchid a member of one species but not another, similarly insects?

Tinkerbell

[Meta menardi]

That is a big question, I think it may help to read a short bit on Cladistics, as that sort of leads to the answer to your question.

If you follow this link,
Lecture 5 - Cladistics
and scoot past the first bit if it doesn't suit you, you will get to a bit titled

Let´s look at a specific example of a cladogram.

The rest may help you understand the reason for "species".

I hope this helps, though I could well understand that it might not.

I like spiders, this link will take you to a cladogram of spiders, albeit for the Netherlands.
http://www.welokee.nl/spiders/en/clades.php?fam=zor

[Jason Green]

Originally Posted by Tinkerbell

Can anyone explain in simple terms why something is classed as belonging to one species and not another?

To answer it in the way you ask, perhaps try thinking of it like this. Each species' name is like a unique combination of physical characteristics - though some may be physically-identical, and only differ in terms of the DNA and/or with some, genitalia (insects).

So, according to this the hoverfly characteristics and DNA unique to the fully-resolved species-level name of Eristalis tenax will only truly fit certain hoverflies (which are E. tenax). Of course, whether you actually acknowledge such features correctly and get to the right identification is down to experience!

I hope this helps.

[King Edward]

Wikipedia has a pretty good species page which is worth reading if you haven't already. See also taxonomy, and various of the linked pages (e.g. Species problem). Unfortunately, no single definition of what constitutes a species is appropriate for all groups of organisms, and some things are never going to be categorised very neatly.

Also, you've got to bear in mind that we're trying to recognise 'species' in the present, whereas in reality populations can be quite dynamic over time with expansion/contraction/movement of ranges (especially with the ebb and flow of ice ages etc.), all with associated interbreeding/hybridisation when populations come into contact.

[fairplay]

Originally Posted by Tinkerbell

Can anyone explain in simple terms why something is classed as belonging to one species and not another? Some bird types may be fairly obvious, but why for example is one orchid a member of one species but not another, similarly insects?

Tinkerbell

I think what Tinkerbell was really asking is why do Orchids not all come under the same Genus (rather than species)

Neil.

[Meta menardi]

Originally Posted by fairplay

I think what Tinkerbell was really asking is why do Orchids not all come under the same Genus (rather than species)

Neil.

You are quite right, this is why I suggested reading about cladistics. It should help to explain how things are sliced and sliced again, till you get to Family or Genus or Species.

[King Edward]

Sounds very plausible. Either way, orchid taxonomy is a mystery.

[RoyW]

Originally Posted by fairplay

I think what Tinkerbell was really asking is why do Orchids not all come under the same Genus (rather than species)

Neil.

I would think that that's something that Tikerbell would need to clarify.

Either way, it's pretty much the same thing, it's just that there are considered to be smaller differences between species within a genus, than there are between two species in different genera!

In simple terms, there are no fully defined rules about what constitutes a seperate species (or genus) - which is why there is regularly disagreement on taxonomic issues between different organistions/scientific bodies/authors.

Evolutionary theory states that new species (and genera) are formed gradually through accumulated small changes - so there is no clear point at which a line can be drawn between two different species.

[Dorts]

Why do orchids not all come under the one genus? Wow!
Just as with all plant family's, when the differences between plants become either morphologically or biologically so different, then plants of those groups will be placed in seperate genera. These generic 'labels' are of course in many cases quite arbitrary, though now, with the advent of dna analasis, it is becoming somewhat easier to place species in their 'correct' genus.

Orchids, in an evolutionary sense are the most actively advanced and the most recent of all groups of plants. They can be found in every region of the earth except Antartica. There are well over 25,000 different species from nearly 90 genera. There are also well over 100,000 different known hybrids, (most of which are man-made).

The variation that can be found is probably greater than in any other plant family. Though placing them into genera has not proved to be easy, it certainly would be impossible to have them all in one genus, such are the obvious differences between many.

The same question could I suppose be asked of the grasses, or any other large plant family, which would yeild a similar answer.
Dorts.

[Tinkerbell]

Goodness me - what a lot to take in! When I've got a few minutes I'll have a go at following the links. Thanks folks for your help.

Ann