Whoa. Like, Whoa dude. How many Vampires can be supported by the population of Sunnydale, CA, the city in which Buffy, The Vampire Slayer, slays her vampires? Well, this dude at Stanford has figured it out for us and if you scroll to the bottom of the page
here you can see a pretttttty nifty graph of the human and vampire populations spiralling into equilibrium.
Rock on dude, Rock on.