ICE-AGES, IMPACTS, & DISEASE - oh my!

     It was just something that came up the other day in conversation but it left me wondering about the causes of extinction in plants and animals. It can't always be impacts, supervolcanoes, and ice-ages. Nor would it be fair to always blame humanity for these problems (though I'm sure with our worldwide presence and relative ease with which we can travel we do share some of the blame). After all, over 90% of all the species which have ever lived are extinct and were extinct long before homo sapiens entered the scene. As George Carlin would say, "We didn't kill them all. They just disappeared. That's what nature does."

     It had me wondering what role disease has to play. White Nose Syndrome is devastating bat populations in North America. Mortality rates make the Black Death look like a walk in the park by comparison. 90%-95% of bats who contract this fungus die and at this point I'm not even sure if those "lucky" 5 or so percent are naturally immune or simply got lucky. But still, it's like the Drafa Plague for bats...

     Fossil records only show that species have gone extinct and can only date those extinctions relatively or within a plus-or-minus of thousands to millions of years. With rare exceptions like the K-T Extinction event which famously wiped out the dinosaurs can it be shown that 80% of the species alive at the time perished in short order but even then, it only happened instantly in geological terms. Overall hundreds or even thousands of years may have passed before that 80% threshold was reached.

     But still, what of disease? Recorded history has only been around for a mere 6000 years and it's only become detailed recently. Yes, humans are responsible for some extinctions like the dodo bird but I don't think it's productive to reflexively blame humanity as we haven't been around long enough to notice how else the Earth disposes of species.
      Even if the White Nose Syndrome isn't 100% fatal, could it crash the bat populations to the point where it would be impossible for them to recover? The disease was only noticed in 2007. If a thousand years is the blink of an eye in geologic time, what is a decade or two? Is it possible that several bat species will have gone extinct before 2017 or 2027? And if so, how often has something like this happened? Viruses, bacteria, and fungi are insidious creatures and the former two have had quite a head start evolutionarily speaking.

      I don't know but like I said...it makes me wonder.