We are familiar with the stories of monsters preying upon humans. Cliques of vampires roving the cities, packs of werewolves roaming the countryside, and everyone everywhere at risk of becoming dinner of both species. Would-be worriers have to wonder if there is a monster around any corner. Yet we have in our grasp the means to determine the extent of the threat.
The predator to prey ratio is the numerical ratio of predators to the number of prey they consume. This ratio remains constant across time. If the number of prey increases, the number of predators will increase until the ratio is reestablished. If the number of predators exceeds the ideal ratio, the number of prey decrease until predators starve to death, and the ratio is eventually re-established. The alternative, of course, is the worst case scenario: that is when the predators eat all the prey and then both populations become extinct. This is also the case for any creatures that may prey upon human beings.
For cold blooded predators, like alligators and crocodiles, the predator to prey ratio is 1:10. For warm blooded predators, such as cats and dogs, the predator to prey ratio is 1:50. However, any creature that feeds on humans has a slow-reproducing and highly defended prey. Wolves can be reassured that any surviving rabbits will double their numbers the next year. For humans, though, the rate would be 20 years under ideal conditions. However, human history has not been ideal.
Let us look at a few assumptions we will use to determine the human predator to prey ratio.
First, the typical human growth rate when plagues and starvation are at bay has been about 3% per year. For most of history, though, hunger and disease took a large number of the population. This would reduce the estimated growth rate to about 1%. However, the population growth rate through history, up to the 1700s, was about 0.1%. What does that mean? Let’s look at the numbers.
| Average human population growth throughout human history | 0.1% |
Natural human growth rate | 1.0% |
| Population excess that has disappeared throughout history | 0.9% |
Let us assume that the difference between the 1% potential and 0.1% actual growth rate is consumed by prey. This means that:
| Population excess that has disappeared throughout history | 0.9% |
Available humans for consumption per 100,000 | 900 |
If the world population was 500 million, then the number consumed by any kind of creature would be:
500,000,000 x 900 = 4,500,000 or 4.5 million people
100,000
That means less than 1% of the population was being consumed by any kind of creature at any one time.
If the potential human population growth rate was actually lower than the 1% value, then the observed prey population would also be lower. However, we want to determine the maximum ratio of monsters to humans, so we will continue looking at the maximum values.
Let us look at the maximum number of vampires that could exist.
The assumptions would be:
| Number of vampire feedings per day | 1 |
Number of humans consumed per day | 1 |
| Number of humans consumed per year | 365 |
If there are 900 unaccounted for humans (prey) per 100,000, then the average vampire would need a prey population of:
365 humans x 100,000 divided by 900 available prey = 40,556 humans
This means that for one vampire to survive, it would need a minimum of almost 41,000 humans in order to have sufficient food without decreasing the population. This gives a predator to prey ratio of 1:40,556.
Vampires hence require a much larger prey population than more natural prey. Barring access to busy roads, an isolated rural village would not support them. If the innate human growth rate through history was lower, then a vampire would need even more humans in its territory to feed upon. Cliques of vampires now become highly unlikely, except in major cities. A city of 500,000 can support a maximum of:
900 potential prey x 500,000 divided by 100,000 x 365 days = 12.3 vampires
Since vampires typically don’t occur in fractions, a medium sized city can thus contain a maximum of a dozen vampires. Larger cities, such as modern day LA, would allow for a vampire social life.
Per the 2000 Census, the metro LA area held 9,519,338 potential prey. That would support a population of 234 vampires. Large enough for their own clubs and rave parties, and perhaps even their own private enclaves.
What about the werewolf? Vampires are thought to haunt modern metro areas and historic rural mountain enclaves, especially in Eastern Europe. Werewolves, however, are found in paintings everywhere from Europe to India. Are werewolves more versatile in habitat or are they forced to cover larger areas in their search for food? Let us see.
We shall assume the same 900 people per 100,000 available for consumption per year. Werewolves, however, are only werewolves one night per lunar month. Hence, they are only werewolves one night out of every 28. If werewolves must feed while in that state, then they only need to eat once every 28 days. If they can control themselves, are on a starvation diet, or are left only hunting lonely wanderers on the heath, then we shall assume one human per feeding, as was the case of the vampires.
| Number of werewolf feedings per 28 days | 1 |
Number of werewolf feedings per year | 13 |
| Number of humans consumed per year | 13 |
For the same assumption of 900 available prey per 100,000 humans, then the population base required to support one werewolf would be:
13 humans x 100,000 divided by 900 available prey = 1,444.4 humans
The werewolf predator to prey ratio is therefore 1:1,444.
Let us assume that people, too, do not come in fractions. That means that the lowly werewolf can survive by feeding on a much smaller population than vampires could. The availability of prey will, of course, affect species behavior.
A large village or even several small villages of several hundred humans could thus support a single werewolf. Werewolves are portrayed as solitary creatures of the wild areas. And given their lesser need to feed, they are better suited for the rural, mountainous habitat. However, vampires are only supportable in larger population centers. To make matters worse, vampires are more often shown to travel in small groups. Perhaps it is a defensive mechanism to protect them from would-be vampire hunters. Perhaps the behavior is of assistance in hunting, since they must feed every night. Werewolves have a natural camouflage of appearing human for the remainder of the month. Werewolves also would have more freedom to safely wander in human form from area to area before resuming the hunt, decreasing their odds of detection.
What does this mean for the average horror fan or would-be monster hunter? Predator to prey ratios affect the behavior of the species, and the difference in sustaining populations leads to very different scenarios. Lonesome travelers on back roads or back woods recluses are hence most likely to be werewolves. Cliquish but highly social partiers would thus be most likely to be vampires. Whether the two species may have also come to some sort of accord to divide up their prospective territories is still unknown to us mere mortals.
