What is a Species?

How do you define a species?
Is species defined on a continuum or is it concrete?
Do your religious or philosophical beliefs color your view of species?
Is your definition for species different from those of your family or friends?

"What is a species?" - it is a simple question that we often ask in our intro biology courses. It's an incredibly difficult concept to address, and is often a topic of great debate. Sure, everyone comes to class with some practical, working definition of a species. But it's amazing just how different those definitions can be. As a plant biologist, my definition tends to be a bit more indistinct than most - and it is constantly in a state of flux. Nomenclature is a tricky thing. As we learn more about each plant community, we see that there is far more going on than we might otherwise think.

I think that most people will agree that these two organisms are different species:
vs

But what about these two?
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What is the distinction between a species, subspecies, and varietal? I have news for you: that line is very different depending on what plant family, and even depending on whether or not that genus is of economic importance or aesthetic appeal.



You can have two plants that are completely different species that look identical. In that case, it pretty much boils down to the underlying chromosomes. How many copies? If one species is tetraploid and the other is triploid, they will not be able to interbreed, which means they are different species.

For example, look at the sage brush of the great basin. On one side of a certain stretch of I-80, they are diploid. On the other they are tetraploid. They look IDENTICAL to the naked eye. They even look identical under a dissecting microscope. But when you try to cross them, they cannot interbreed. With a little sleuthing, you can determine that they have an entirely different karyotype.

What does this matter to you?
It probably doesn't matter at all. But it's interesting to me. And therefore I started a thread.
How do you define species? Do you think it's really very cut-and-dry?

 

I hate to say it...but it will probably get more complex if we ever discover life on other planets. (However "life" is defined...)
I've studied Astrophysics...I'm fascinated by Astrochemistry...I guess the next step would be Astrobiology.

Actually, it is interesting to me...one of the most recent, is if we find something in the bottom of the underground lakes in the Antarctic.
Although likely this would be different species of micro-organisms.

It's important to know your varieties.

 

Is this similar to a mule...a sterile interbreed of a horse and an ass, two distinct species??