To illustrate the difference so noted:
Genus is an arbitrary category.
Yes. And to complete confusion between the continents with respect to deer species, the animal we call an elk (or wapiti) in North America, is very close to what the Europeans call a “red deer”. They used to be considered the same species, but based on recent DNA evidence, they are now being classed as “Cervus elaphus” and “Cervus canadensis”, rather than the North American animal simply being a subspecies of Cervus elaphus.
So is species, as far as that goes. I don’t understand why you chose to lump foxes in with dogs and wolves as examples related to the OP. Can you explain?
Yeah, I saw that, too. Elk are probably more properly called ‘wapiti’, but Americans can’t be bothered with difficult words.
I don’t know that it makes sense to say what the proper word is. I never in my over 50 years heard a moose called an elk until just recently. Wapiti is the Native American (Shawnee) word, sometimes used in English. Moose and elk are the [American] English words.
If you asked 100 Americans what a “wapiti” is, I doubt if even 10 would be able to answer. Seems to me that it would be a terrible word to use, in general, since most people wouldn’t understand it.
Yes. We should all use words from another language, from another coast. And should have no problems with difficult words that are three consonant-vowel syllables. How do you pronounce your name again? Tcheef-gooey? 
I think taxonomically, dolphin is a type of whale, but not always in common usage.
Crows and ravens are different species, they just look very similar. The have slight size, plumage, and behavior differences.
Wolves and dogs are the same species. Foxes are not. I don’t think they can breed. The domesticated silver fox is to wild fox as dog is to wolf. A completely different species, but I just want you to “awww”:Fennec foxes.
There are many species of squash, but yes, pumpkins are the same species as some species of squash.
The popular game fish “trout” refers to several genera of fish. Some are true trout (rainbow, cutthroat troats), some are char (lake, brook trouts), and some are classified alongside salmon (brown trout)
Just a fun fact based on the OP: Although many deer are sexually dimorphic, ALL reindeer have antlers, not just males. If Santa is being pulled by some without antlers, someone didn’t do the research. (Apparently some don’t have antlers, but the majority of females do). And males supposedly lose theirs sooner.
If we’re talking taxonomy, we’re talking science, and “whale” is not a scientific term. The term is cetacean, of the toothed or baleen variety. Dolphins are toothed cetaceans, like [colloquial] Killer Whales or [more scientific] Orcas.
Species is a biological reality, albeit one with fuzzy edges and that’s often hard to nail down. Taxonomy is just a bunch of arbitrary groupings devised by men with beards, based on things like morphological similarity.
In many cases, taxonomy is a fair representation of the phylogenetic tree of relatedness, but the correlation is quite loose. There’s no particular reason why we must always assume that two species in different genera are more distantly related to one another than two species in the same genus.
Not really. The reality part, that is. It’s a human construct.
But you still haven’t explained why you lumped foxes in with wolves. Why not lump in squirrels, too?
A lot of people in Alaska refer to grayling as trout, and cutthroat as salmon. It’s a slippery slope.
Species is reality in the sense that it describes a group of organisms that interbreed with one another (as mentioned, there are fuzzy edges, and the ‘hard to nail down’ bit includes whether we mean ‘can’ or ‘does’ interbreed with one another). Sure, it’s humans that think that means something, but it has tangible reality of a kind that taxonomic descriptions don’t, necessarily - the taxonomic groupings were decided on a different basis.
The animals we call ‘foxes’ are not a single distinct group, in terms of phylogeny - there are things called foxes sprinkled in amongst pretty much all of the branches of the family tree.
I think I’m going to just agree to disagree in this forum as to take this any further would stray into GD territory.
OK. In looking at the Wikipedia article, I can see that the Ethiopian wolf is sometimes referred to as a fox. I didn’t know that.
I guess it depends on whether you’re talking about species as a purely taxonomic concept, in which case, I would agree, it’s arbitrary, but the term ‘species’ has other uses that are more useful and have more of a grounding in reality.
Yeah - if you look at this typical diagram of the phylogenetic relatedness of dogs etc, the nomenclature is pretty mixed (which is what this thread is all about - any system of naming that isn’t based on actual relatedness may appear to lump or split things that don’t deserve it)
My favorite is the Chilean sea “bass” you can find at fancy-ish restaurants. The “real” name for it is Patagonian toothfish and they look like this. A bit of euphemism in action.
The old school definition for species is if animal A and animal B were to mate but can’t produce offspring, then they are separate species. Of course more recently that is seen to be a very poor metric of classification. Even ligers and tigons can have offspring in rarer circumstances.
What do you mean, an African or a European pigeon?
If by “more recently” you mean the whole of recorded history, sure. People have been well aware of the existence of hybrid species for as long as written records have existed.
Like what? Animals that are usually man-made, like mules, ligers, etc. are not normally fecund. Would we have known about a hybrid species that maintains a stable wild population, even if it sort of looks like another species? Like what I understand from the history of the red wolf. There may have been speculation, but people probably either assumed it was its own thing, or didn’t care. Genetic methods came later to confirm that yes, species X is fertile but a hybrid.
Mules woudl eb the obvious one.
You don;t need genetic evidence to know that your donkey fucked your horse and the horse produced an animals that was a little like both parents.
That’s how the salmon can leap their way up it (the slippery slope)