Clive has discovered this excellent paper (PDF) entitled “Ghosts, Vampires and Zombies, Cinema Fiction vs. Physics Reality”. In particular, he’s interested in the section about the viability of human and vampire populations.
The paper concludes that because when vampires kill humans they make new vampires, the human population of the planet would be eliminated in less than three years. I made a little chart of their data (click for a larger version):
I’m guessing that last couple of months would be very 28 Days Later.
Clive then goes on to speculate about how a vampire slayer (say, Buffy Summers) might manage the population the way we occasionally cull deer:
So the really sweet spot seems to be months eight to ten — when the vampire population would range from 128 to 512, respectively. Those seem like realistic numbers of vampires for a slayer to kill in a single month, assuming she kills 2 to 8 per night. With that kill-ratio, a slayer each month could kill enough vampires to knock the population back a month or two.
Clive says he’s not a Buffy fan. As such, he (and the researchers) understandably skips over some key factors in Buffy mythology. Let me see what I remember:
- Not all humans killed by vampires get turned. In fact, in most popular myths, it’s actually quite a rare occurrence. I’d guess the rate of new vampire to humans killed by vampires might be, I don’t know, 1 to 100.
- The researchers suggest that a vampire feeds once a month. In the world of Buffy, they seemed to eat a lot more often than that. As I recall, the only night they took off was Halloween.
- Buffy and her colleagues occasionally kill a whole schwack of vampires. At the current growth rate, she surely would have killed off 500 or so by the end of season two.
- In the show’s final episode, there are a crap load of vampires. Like, maybe, thousands? I don’t remember all that way.
I thought the obsessive stats at BuffyWorld might have helped, but they don’t have totals for every episode.
DarrenBarefoot.com 
But, as Buffy lived in Sunnydale – conveniently situated on top of the Hellmouth – she had access to a statistically larger pool of Vampires than in the average suburban/metropolitan area.
Does that mean her average kill numbers would be higher than a slayer fighting in, say, Boise?
Also – wouldn’t fighting vampires at their source (the Hellmouth) allow her slayage to have a greater impact on the initial number of vampires?
Damn you, Darren. I’m going to be thinking about this all night.
Yeah, that’s a good point about the Hellmouth. I think that would just enable her to kill off all the vampires more rapidly?
but darren, as vampires, wouldn’t we also be significantly sexier? this needs to be considered very carefully.
Darren!
I am completely giggling at the idea of you perousing the Buffy Fansites.
You rock.
Heather makes a good point about the Hellmouth…. if she lived anywhere else… dullsville.
-jules
In order to “birth” a new vampire the human must also feed from the vampire… the human victim must drink from the blood of a vampire therefore the turning of vampires is usually deliberate.
The massive vampire force in the final episode have been gathered (From where? not earth proper) by the FIRST (the first evil, the ultimate bad guy) at the entrance to the hell mouth… here they are waiting to be unleashed until BUFFY ROCKS THEIR WORLD = oh, yah!
On March 21st a Season EIGHT comic book is due to be released… written by Joss himself.
– Meg