What species can be found in the largest portion of the earth geographically? Are there any species that are virtually everywhere?
Thanks for all replies
AllFree
If you really mean just a single species, I suspect it’s us. Humans. Or rats. They pretty much go wherever we do.
Keep in mind that it’s a whole different ball game if you talk about marine animals. It’s hard to compare terrestrial and marine animals in this sense.
Homo sapiens.
considering Terrestrial or marine animals, would Plankton be found in the widest range in terms of three dimensions considering it’s dispersal through the oceans at wide depth levels?
Tardigrades can and do live pretty much anywhere. They’re also adorable.
Yes Marshmellow, didn’t know about Tarigrades specifically but my immediate reaction to the question was bacteria of some phylum.
Tardigrades are not a species, however, they are a whole damn phylum. According to the Wiki article linked to by marshmallow, “More than 1,000 species of tardigrades have been described,” and that probably means that several thousand species actually exist. There may be tardigrades of one sort or another almost everywhere on Earth, but it does not follow that any one species of them is particularly widely distributed.
I suspect there will be similar complications involved in getting a clear sense of the distribution of particular types of bacteria and other types of microscopic organisms too. That is, the names commonly used to refer to types of bacteria (or protists, etc.) often apply to groups well above the species level in the taxonomic hierarchy. Of course, species boundaries, and even the very concept of species, get a bit fluid with organisms of this sort anyway.
ETA: Plankton are not a species either. It is not even a taxonomic group. Different types of plankton may be scarcely related at all. Heck, some are animals and some are plants.
I think it’s us and dogs. Dogs are in the high Arctic with Inuit, but rats aren’t.
As others have noted, for expanded distributions humans and their commensals are the indisputable winners.
In terms of natural distribtuions, bracken fern is considered to be the vascular plant with the widest natural distribution. It occurs pretty much everywhere below the treeline.
The peregrine falcon is probably the most widely distributed terrestrial animal, occurring on every continent and most larger islands. It is really only absent from the denser rainforest areas and the absolute driest deserts. It’s hard to think of another species with a wider natural distribution
Surely it would be something like E Coli, or a Staphylococcus species, or Candida Albicans, or maybe a virus of some type.
E Coli, for instance, is present in pretty much any warm-blooded gut, and warm-blooded guts are pretty widely distributed on both land and ocean.
Since the dogs and humans will have various parasites such as mites and worms, and those parasites will live without dogs and humans, the parasites probably win. The common mange mite is probably the winner.
What’s the distinction between the distribution of humans and a natural distribution?
Houseflies ?
“Natural” being not aided or caused by humans.
I’ve never seen a city without pigeons. I know they’re not in the top ranks here, but they’re pretty ubiquitous.
How many species of pigeons are there?
Sorry, missed this one: How many species of houseflies are there, Gymnopithys?
If we’re talking about species, then these sweeping generalities don’t work.
Huh. This means humans have no natural distribution and are, therefore, probably from some other universe. 
I had never heard of those, but reading this wikipedia article, they’re fucking impressive. No way to get rid of them. Dessicate them, they survive. Boils them, they survive. Plunge them in liquid oxygen, they survive. Try to kill them with gamma rays, they survive. Cruch them under a 6000 ATM pressure, they survive. If, fed up, you just decide to kick them out of the planet, they still survive in the vacuum.
I, for one, welcome our future tardigrade overlords.
They are cute though. They look just like a big sumo laughing mummy and I have a few of them around here somewhere that I keep as pets.
Musca domesticus is a single species.