My father forgets that I have lousy eyesight and am terrible at IDing birds. We were somewhere tropical and he asked me what that bird that had just flown off looked like. Me: It was small and brown. He made many upset noises.
In many cases, whether the lizards themselves care is precisely the point that isn’t known. Maybe some of the lizards in a particular region have a tiny orange spot above the eye, and some don’t. Is this just an incidental variation between individuals in a single species, like hair color in humans, or is it two different species? Most likely, members of the two populations can produce fertile offspring together, if they mate… but will they mate? It might be that the orange-spot lizards will only breed with other orange-spot lizards, and the spotless lizards will only breed with other spotless lizards. In such a case, they clearly do care very much whether another lizard has an orange spot. And if that’s the case, then the two populations are two different species.
But it’s very difficult for the herpatologists studying them to know that, without very extensive study of their behavior in the wild.
Once again, a flippant, off-the-cuff remark gets me in trouble. But I posit that for at least a few species the male will mate with anything it can mount. Even an old boot would suffice.
In most species with mate selection, the male is much less discriminating than the female. Female choice is the most common mating strategy. This is because sperm are cheap to make, while eggs are much more expensive. It generally costs males relatively little to try to mate with anything that comes along, while females can lose their reproductive investment for the entire year if they mate with the wrong male.
In many cases courtship displays indicate to the female that the male is strong and vigorous, and has been getting plenty of food and has no defects. Males put a lot of energy into singing all day or all night long, jumping around, dancing, doing pushups, etc, just to prove to females that they’re tuff stuff.
But they can make an educated guess. If spot color is important in mating recognition in other related species, then very likely the two forms are different species. As I said above, taxonomists pay particular attention to characteristics that are known to be important in mate recognition in particular groups. One of the factors that has contributed to the splitting of many bird species is the increased amount of information on vocalizations. This can extend to the playback of recordings of other forms to see if the form in question responds to that song.
Which implies that they’ve already done that difficult and very extensive study of other related species in the field. But there had to have been a point before anyone realized that spot color was relevant at all, before which point those lizards probably would have been regarded as the same species (especially if researchers captured some of them and watched their behavior in captivity, which can be very different from wild behavior, and saw them mating and producing fertile offspring in the lab).
I’m not saying that wild mating patterns can’t be studied at all: Obviously they can be and are. It’s just a lot of work, especially since you don’t necessarily know all of the traits that the lizards themselves find relevant. Heck, for some species, there haven’t even been enough individuals observed to say anything about their mating habits (beyond guesses based on whatever more numerous species appears most similar).
You’re exaggerating the amount of research really needed. Most courtship displays are highly visible and easy to observe. For most vertebrates, we have a pretty good idea of the kind of features that are important, and have known it for more than a century.
Before the Biological Species Concept gained traction in the 1950s, the prevailing species concepts were the Morphological and Typological Species concepts. They would have probably classified the two forms as different species just on the basis of the morphological difference.
Look at the vastly different varieties of the Dark-eyed Junco. (Just google Dark-eyed Junco varieties if you (by you I am referring to the average reader and not Colibiri) don’t know what I am talking about. There are thousands of references out there.) If I were classifying them based just on their physical appearance I would have said there were at least three or four different species. Interestingly, the varieties are not necessarily geographically separated. I have seen three different varieties at the same feeder at the same time.
And you may be correct 
. Formerly they were five species, then they were lumped, now there is talk of splitting them again into at least three. Or maybe not.. Science marches ever on.
Many of them are migratory, so they will definitely co-mingle in the winter.
They are separated on their breeding grounds. On migration and during the winter, several distinct forms can occur together.
All the major forms were originally described as distinct species. IIRC, they were merged in the 1970s or thereabouts because they extensively hybridize where the breeding ranges meet.
Application of the Biological Species Concept led to a massive lumping of bird species from the 1950s to the 1970s. Finding that such distinct forms as the juncos, Bullock’s and Baltimore Orioles, and Yellow-shafted and Red-shafted Flickers hybridized led to greatly increasing the degree of difference that was accepted to lump allopatric populations.
Currently, the Biological Species Concept is interpreted somewhat differently. Formerly any hybridization would justify lumping; now if hybridization is only occasional or limited to a narrow zone the forms will be recognized as separate species. On this basis, Bullock’s and Baltimore Orioles, which had been merged as Northern Oriole, were re-split, while Red-shafted and Yellow-shafted Flickers have remained lumped as Northern Flicker.
That corresponds to what I have seen. I only see them in the colder months. I was told they move to the higher elevations in the summer. It would be interesting to see if there is more than one variety in the mountains around here at this time of year.
I’ve increasingly been made aware that the lines between species is fuzzy and gray, instead of black and white. Have there been any attempts to change the system where speciation is not binary, and there are separate classes. Like maybe a term for those line the OP where they genetically seem entirely able to breed and produce fertile offspring, bit behaviorally don’t except in rare cases?
In other words, if all the competing classification systems call them s sepate species, you have full species, but get various other classifications if they disagree. And not just calling them a subspecies, as that is explicitly on the “not a new species” side.
At this time of year, only the locally breeding subspecies will be present.
Don’t tell me too much or you will ruin my excuse for a long afternoon in the mountains.
I wouldn’t see much point. There are a wide variety of cases intermediate between full species and subspecies. Even if you had more than two categories, you would still have to draw lines between them. You would just have to draw more lines. This said, biologists do recognize such things as species complexes and superspecies (a group of closely related species with separate ranges).
I would also point out that there are plenty of species that are universally regarded as “good” species which still can produce fertile hybrids in captivity, such as most species in the genus Canis (wolves, coyotes, jackals) and in the genus Anas (many common ducks).
Why do you need an excuse?
I guess I don’t have to have an excuse but it’s more fun for me when I have an objective or a goal to accomplish. Would anyone be interested in my observations if I ever get around to actually doing this?
If you find a new species of lizard, sure.
It can get messy quick though. The utter taxonomic chaos around the Red wolf/Eastern wolf being a case in point. Pretty much every species concept works broadly, but struggles with fringe cases (often different fringe cases for different concepts).
Right. But AFAIK no one regards the Gray Wolf (sensu strictu) to be the same species as the Coyote, since they maintain separate identities over most of their ranges, even if they may have produced hybrid populations or species of hybrid origin.
Then on top of that you’ve got hybridization with domestic dogs. The Coyotes currently spreading through Panama toward South America seem to have some dog genes.