More Predators Than Prey

In order to make an environment more hazardous, creators of fiction will often include aggressive predatory beasts that occur in far larger numbers than should be possible given the environmental conditions shown. In Real Life, the larger a creature is, the more energy in the form of food from a suitable source it must consume in order to both grow so large in the first place and to sustain itself on a daily basis. If it is very active it will need even more calories just to survive. Despite this, there will often be a veritable horde of wild, aggressive beasts that roam a desolate wasteland or almost lifeless underground tunnels without having prey to feed on and without attacking each other. Such beasts will often be absurdly persistent when encountering humans, attacking them seemingly out of hunger that overcomes all sense of self-preservation. This occurs even if their fellows fall like flies around them, and they will never pause to gorge themselves on these fresh bodies that should appear a ready and far less risky food source to them. Could the considered the ecological counterpart to More Criminals Than Targets: in both cases, adversaries appear in far greater numbers than their circumstances could support.

Common in post-apocalyptic fiction and on Death Worlds; in contrast to Real Life, large predators in these kinds of works seem to be less susceptible to the kind of events that should cause them to be severely depleted or go extinct than the smaller creatures they normally feed on. In fact, they often mutate into something far more powerful than their original form while at the same time getting by with less sustenance.

Some works might try to justify it either In-Universe or All in The Manual,with the proper food sources simply being unseen.

Examples of More Predators Than Prey include:

Film

Pitch Black plays on a Desert Planet, and one of the only two species the protagonists encounter are predators which are very much into human flesh. They occur in numbers which no desert biome can possibly provide enough herbivores for. To make things worse, the animals can only hunt in the dark, so their only opportunity to come to the surface for prey is one month in 22 years during an eclipse of the Binary Suns. Not that they are hibernating through all the years in between.
- It's implied that there's a whole ecosystem underground that supports the creatures, so their appearance and behavior on the surface is more of a once-in-a-lifetime feeding frenzy than it is, their usual means of subsistence.
Reign of Fire, wherein the entire non-microbial population of the world seems to be humans and non-cannibalistic dragons the size of whales. However, the dragons are shown to start eating each other later in the movie. Also Lampshaded, as it was stated that the dragons would eventually start to starve and go back into hibernation, which is apparently what happened the first time around with the dinosaurs.

Literature

In The Tough Guide to Fantasyland by Diana Wynne Jones, she uses this as a key pieces of evidence for the theory that fantasy worlds' ecosystems have been recently ravaged (another is the way piles of refuse around oppressed peasants' huts don't just rot away.) She comes to the conclusion that the systems are re-establishing themselves with humans at the bottom, and everything will be fine.
Blindsight had an interesting quasi-example in the case of vampires - the human population couldn't expand fast enough to support a population of vampires, so vampires evolved the ability to enter long-term hibernation in between feeding periods so that the human population would have a chance to replenish itself.
Lampshaded in The Lost World, as they actually ask why the island has more predators than the prey should be able to support. The stated justification being that prions from the sheep-based feed they were given caused most animals to die young and be scavenged by the predators.
In H.P. Lovecraft's The Lurking Fear, the mutated deformed cannibals number in the dozens, if not hundreds, while their abode is rather isolated and the number of people who fall victim to them is small.
Nearly all animals in the Forest of Septimus Heap are carnivorous (or man-eating). Other animals almost never mentioned.

Tabletop Games

Gary Gygax recognized that Dungeons & Dragons had this problem and tried to justify it in the 1st Edition Dungeon Master's Guide.

So many of the monsters are large predators that it is difficult to justify their existence in proximity to one another. [snip] Here are some suggestions. Certain vegetation grows very rapidly in the world - roots or tubers, a grass-like plant, or grain. One or more of such crops support many rabbits or herd animals or wild pigs or people or whatever you like! The vegetation springs up due to a nutrient in the soil (possibly some element unknown in the mundane world) and possibly due to the radiation of the sun as well. A species or two of herbivores which grow rapidly, breed prolifically, and need but scant nutriment is also suggested.

- Early D&D also had climate-appropriate herbivores on its random encounter tables. If they were removed it was presumably trimming, there not being much one can do with camels aside from staring at them. On the other hand, getting in the way of a herd of bison is all sorts of exciting.
- Justified in the lower planes - most fiends don't need to eat at all and seek prey For the Evulz - so an infernal environment could have Hungry Jungle with nothing but predators.
GURPS: Dungeon Fantasy averts this trope, advising GMs to give some consideration to the balance between predators and prey in an ecosystem.
In Magic: The Gathering the green faction of New Phyrexia, the Vicious Swarm, is attempting to be entirely predators that prey upon each other. This works better than other examples because they don't actually need sustenance, cutting out the primary producers and herbivores as necessary components to the ecosystem.

Video Games

The Fallout series of games have numerous examples of this: nuclear war and subsequent collapse of society has left most of the world a barren desolate wasteland with deadly radiation occuring here and there. Despite the fact that there is little prey for them, giant versions of real critters like scorpions or even flies run around, seemingly attacking only the player character and never any other creatures.
- In Fallout 3, monsters of different species will fight each other, up to and including Albino Radscorpions killing Super Mutant Behemoths if they spawn near each other. On the other hand, the number of predators seems proportional to the player character's level—Giant Mole Rats seem to die out around level 15.
The computer game Metro 2033 has a very strange ecology at work: The surface world has been in the grip of nuclear winter for twenty years, nothing grows there and the air is toxic. The remnants of humanity hide out in old metro stations where the only food sources are domesticated pigs and cultivated mushrooms. The tunnels between the stations are typically infested with hideous mutants that 1) are mostly larger than humans and also faster and stronger, 2) constantly attack humans in order to eat them, 3) never seem to attack each other, despite the fact that there is more meat on their fellows than on humans. A particulary silly example is how the winged beasts called demons will swoop down on human prey that is capable of shooting at it, but leave the far more numerous nosalises (who only have their claws and teeth) alone, even ignoring the bodies of the ones you have already killed.
In Knights of the Old Republic II, on Telos, there are Cannocks (and Bounty Hunters), which are at the very least hostile and onmivorous, but no "peaceful" or herbivorous creatures. If you point this out to Bao-Dur he reminds you that the planet's being terraformed and the cannocks were introduced to control herbivore numbers. ThenCzerka Corp hijacked the project, released too many cannocks and sent the ecosystem down the tubes. Dxun has no such excuse, though.
Monster Hunter isn't a perfect example, since you do see herbivores and you do see predators eating each other, but the food chain still seems pretty unbalanced. What are all these giant monsters eating?
World of Warcraft has some serious cases of this; a good example is the Hillsbrad Foothills. There's bears, yeti and giant spiders all over the place, but no major herbivorous beasts to feed them. There's a lot of areas like this in WoW.
- Most zones in WoW have "critters" which are small creatures (usually herbivores) that players cannot gain loot or experience from. One may think that critters are an intentional aversion of this trope, but they are never present in anywhere near large enough numbers to feed the vast hordes of predators which populate many zones.
Most Xen wildlife in Half Life is carnivorous. Headcrabs, at least, are confirmed in the sequel to be omnivorous. And you have to wonder what those several billion ocean leeches in Half-Life 2 are eating to sustain their population...
Averted in The Elder Scrolls V: Skyrim. For every bear, sabercat and wolf pack you come across, you see a lot more deers and rabbits. Whether mammoths are preyed on is unsure, what with giants keeping and protecting them as livestock.

Web Comics

On Alternia, everything is considered unsuspecting prey by everything else.