How many types of squirrel are there? Is this squirrel special in some way?
Sometimes I wonder if scientists don't call the lichen on one side of the rock a different species than the one on the other side just to get their name on a "discovery."
Anyone here knowledgeable on what the requirements are to call something a new species? Hell, we don't say blond people are a different species than brunettes. Why does different coloration make for a different species elsewhere?
There is not and will probably never be a universally accepted definition of a species. Within each discipline's systematics there are lumpers, who tend to see fewer species but more races and perhaps subspecies, and splitters, who tend to see more species. Some indications of a valid species include historic genetic isolation (meaning that the group of animals or plants or bacteria has not mingled with other recognizable species in a reasonable amount of time), present genetic isolation (meaning that the group of animals or plants or bacteria is not now interbreeding with other recognizable species), identifying characteristics distinguishable from other similar species, and an identifiable ecological niche. Difference may be color, if two similar but differently colored species breed true and can't interbreed or interbreed according to hybridization rules, but usually isn't.
If an animal is truly unique then it's an easy decision, but most animals are not truly unique. A scientist will look at the spread in characteristics between different similar populations and decide for herself if there is a net difference at genus level, or species level, or subspecies level, or race, or simply diverse individuals. One scientist may see a unique species; another scientist may see a subspecies. It also depends on how you look. A scientist genetically investigating the Mount Graham red squirrel may find it approaching the level of a separate species due to its genetic variation, while another studying its ecological niche and systematics may find it a subspecies and a third studying defining characteristics may find it merely a race. Tamiasciurus hudsonicus grahamensis is currently considered a subspecies of the common American red squirrel, so it's technically an endangered subspecies rather than an endangered species. It varies from the red squirrel in its genetics, size, coloration, habitat, and morphology, so it certainly deserves at least its subspecies status and therefore protection.
It's an academic discussion anyway, as the Arizona Department of Transportation has decided not to build the squirrel bridges just because the Federal Government is willing to borrow money for it.
http://www.eacourier.com/articles/2010/06/18/news/breaking_news/doc4c1bed3801f2c142931203.txt
Kind of ruins my response to TK149 - the real reason they're dying off is probably due to their trees being filled with scientists and tree bridge construction workers. Oh well. For the record, squirrel populations are usually dependent on mast production, and this squirrel has been hard hit by infestations of invasive non-indigenous insect and by drought.