It is often said that when a population of critters splits, and they evolve separately, eventually they won’t be able to breed with each other any longer. This marks an event of speciation.
So what about critters that reproduce asexually? What event marks the moment of speciation for them? At what point do we declare an oak to no longer be an oak, but rather a mighty redwood?
Oaks reproduce sexually.
Please clarify: if a species already reproduces only asexually then it’s already, uh, specified because…you know. No need for anybody else to be in the gene pool.
But I don’t think there are any multicellular organisms that reproduce asexually exclusively. So it would come back around to the point where sexual reproduction isn’t possible due to physiological or geographical impedements.
OK, that’s just scary. Although there’s a “got wood” joke in there somewhere.
Forget trees, then. Deep water snails.
Most snails I am familiar with are hemaphroditic and usually do not self-fertilize.
When the “reproductive incompatability” definition does not fit the biology of a given organism, then other criteria are used. Morphological disparity from a parent population is a good one.
It is not common, but there are some, the whiptailed lizard being a case in point.
Bizarre. I tell you, we got one of everything here on Earth. Sometimes three or four! So each of those hybrids would be its own species, right?
This depends on the definition of “species” used. There are a number of different species definitions available. The most popular one currently is the “Biological Species Concept” (BSC) which defines species as populations which do not regularly hybridize in nature, or, as Ernst Mayr, one of its developers, stated it:
The BSC by its nature can only be applied to sexually reproducing organisms. (It has a number of other limitations as well, since it is difficult to evaluate the species status of closely related populations that do not come into contact anywhere.) For asexually reproducing organisms, generally some kind of Morphological Species Concept is applied; that is, populations that are as different in appearance as good sexually reproducing species are classified as species. Increasingly today genetic species concepts may be applied: if a population has diverged sufficiently genetically it is considered to be a separate species.
There are quite a few multicellular organisms that reproduce purely asexually, mostly plants but some animals as well.