It is a truth universally acknowledged that a hungry vampire must be in want of blood. It is also universally acknowledged that the sucking of said blood makes more little vamplings, whether by direct infection or by a Buffy-esque “whole sucking thing.” Vampires are top predators, and like lions and wolves, their population can’t outstrip their prey supply.
But since there are so many people, why aren’t we awash in vampires? That’s why Laura McLay at Punk Rock Operations Research is skeptical of vampires. Based on a mathematical model of their population dynamics, she calculates that:
The vampire population would either explode or die out, depending on the expected number of offspring per vampire. But if you take into account the fact that vampires live many, many generations (they’re virtually immortal) and may create thousands of offspring, the population explodes (if you assume that each vampire creates at least one vampire, on average, before it dies). With those numbers, vampires would not be living under the radar–they would be everywhere!
But basing her calculation off icky goopy Twilight, McLay makes a critical mistake. She left out human predation on vampires, fetchingly epitomized in Buffy the Vampire Slayer. Brian Thomas, a theoretical ecologist, calculated the vampire ecology and population dynamics of the Buffyverse and found:
This [Thomas' assumptions] results in an equilibrium population of 36,346 humans and 18 vampires. Thomas then notes that interestingly enough the established population of Sunnydale on the show is 38,500 humans, pretty damn close to the equation result. Maybe Buffy needs to cut back on the slaying in order to let the vampires weed out that extra 2100 people, we wouldn’t want human overpopulation to lead to starvation.
But is this equilibrium stable? Will natural fluctuations in the vampire population prevent the equilibrium state from ever existing? Thomas then ran the model using several different initial population sizes and seeing whether they eventually moved to equilibrium, or spiraled off into an abyss where everybody died. Turns out the model is stable and the vampires and humans can co-exist forever! Hooray!
Check out Thomas’ original paper here (PDF).
So, because we are not neck-deep in starving vampires, clearly we are living in the Buffyverse. Down with mooshy sparkly vampires & limp, passive heroines! Up with snarly-faced evil vamps and ass-kicking Slayers! Now where’s my activated Slayer powers?