Food Chain

"I know what we need to do," the ranger said as we fled. "Wyverns are a middle predator: they're small enough to care about humanoid prey, but large enough for dragons to care about them. So what we need to do is find a dragon."

Basic Information

This page has nothing to do with the Food Chains trope, which describes supernatural perils of eating food from an unfamiliar place.

In ecology, the food chain describes the flow of chemical energy through an ecosystem. In short, it describes what eats what, and what is food for what. Generally, the food chain is divided into four or five trophic levels:

The food chain begins with producers: organisms that gather energy from the inanimate environment. This is usually plants or algae gathering sunlight, but can extend to more exotic things like lithoautotroph bacteria converting metal or sulfur compounds, or radiotroph fungus gathering radiation. Another term for producers, incidentally, is autotroph¹; anything else on this list is a heterotroph².

The next level up is herbivores: animals that consume the producers, turning plant, algal, or bacterial matter into animal matter. These are (or perhaps were) also called primary consumers.

Steps above herbivores are carnivores: animals that consume other animals, whether herbivore or carnivore. These, logically, can also be called secondary (etc.) consumers.

The final step in the food chain, and the step that completes the loop of the carbon cycle, is detritovores or decomposers: decay organisms that break down anything not eaten. This includes most fungi and bacteria. These can also be consumed by other levels, which complicate the "chain" somewhat …

(Like many things in biology, these categories aren't entirely firm. Omnivores such as humans or carnivorous plants such as the Venus flytrap can fit in multiple categories, as might more active sorts of detritovore that cause disease. Parasites, symbionts and commensal organisms are also ambiguously placed on the list.)

Worth noting is that only about 10% of the energy at one level can be passed to the next, with the rest being either wasted or expended by the organism. This will usually limit the food chain to about four levels: producers, herbivores, first-level carnivores, and second-level carnivores. Some individual chains are longer, but this typically involves the chain being part of a food web four levels high. The "chain" is also typically pyramidal in shape, both by headcount and mass, with more producers than primary consumers, more primaries than secondaries etc.

Biomagnification

Where poison is a concern, beings high on the food chain tend to be more vulnerable, simply because they are exposed to exponentially higher doses. Consider a chain composed of a plant, an insect, an insect-eating bird, and a bird of prey:

• The plant generates 1 unit of a poison per unit energy. (Assume that nothing in this chain is able to break down or excrete the poison.)
• The insect eats 10 times its energy content in plant matter, so it contains 10 units of poison per unit energy.
• The first bird eats 10 times its energy content in insect matter, so it contains 100 units of poison per unit energy.
• The bird of prey eats 10 times its energy content in bird matter, so it contains 1,000 units of poison per unit energy.

This can very much be an issue where pesticide is concerned. A chemical toxic enough to kill an herbivore could well be toxic enough to have unpleasant effects on an apex predator at 100 times the concentration, even if specifically targeted at the herbivore.³ Some species, however, actively take advantage of this effect and concentrate a poison from their diet to protect themselves from higher level predators. Also, in some cases, an antifeedant may backfire on a species - such as those that produce various alkaloids to protect themselves from their natural predators, only to find humans harvesting them for recreational drugs or spices. Heavy metals are also great bio-accumulators - mercury (the metal) being a prime example, as the Japanese found when it started building up in their costal fish supply.

Sources

Bibliography

1. Wikipedia

2. Thermodynaminomicon

See Also

• To Serve Man - when humanity isn't at the top
• Food Chain of Evil - when even that isn't the top
• Energy - what passes through the food chain
• Entropy - part of why so little of the energy goes through
• Cannibalism - short term gains, long term losses.

Game and Story Use

• Considering what a creature eats, and what eats it, can be useful for designing monsters.
  • Any kind of prey will usually have some kind of defense, whether that means fleeing, fighting back, calling its predator's predator, or using poison.
    • The "summon bigger fish" option, if common enough, could create an ecosystem where the kinds of defenses and weapons an animal has depend on whether it is at an even or odd trophic level.
  • Any predator will usually have some way to overcome its prey's defenses, in addition to whatever it uses to make the kill. This doesn't necessarily make it more dangerous generally (the predator might even become less dangerous, by specializing in overcoming that specific defense), but does make it more dangerous to anything relying on that defense.
  • Scavengers need to either digest things that a predator can't, or have some way of chasing predators from their kills.
  • Large creatures need lots of food. They might hunt large prey, or simply be constantly hunting smaller prey, but a dragon or tarrasque needs to eat a lot.
    • This also means that anything large, and anything high on the food chain, needs to control a lot of territory simply because of the producers needed to support it.
• Any realistic food chain needs to have producers in it at some point. The producers might not be nearby⁴, but they have to exist for the ecosystem to be remotely stable.
  • If the producers in your dungeon are the traditional mushrooms, they might be a treasure in their own right to a biologist: this would suggest that they're able to extract energy from rocks. (Either that, or the dungeon's radioactive or a waste dump for some other biome.)
• Disruptions to the food chain can be what kicks off a plot.
  • An apex predator is locally driven to extinction. Without predation, its prey population explodes, and then suffers a Malthusian catastrophe.
    • To reverse the flavour text, if adventurers take out a dragon, they may end up devastating the region with a plague of wyverns.
  • This happens to a prey animal instead. Its predators are now starving, and wandering in search of new prey.
    • Although long term, this can be a good way to destroy a species … it worked well enough with the Plains Indians (who, granted, were not actually eradicated, but were greatly reduced in population and destroyed as nations).
  • Something destroys all the decomposers in a place. Aside from corpses and waste choking the system, the break in the carbon cycle starts killing plants.
    • This would be a nasty misfire for some sort of spell to remove disease … something meant to cure an infected wound ends up purging a large area of decay microorganisms (let's assume that those that double as gut bacteria are spared or things could be even less pleasant).
• Biomagnification is a decent explanation for making the monster of the week an apex predator: some kind of mutagenic pollutant or Super Serum got taken up by plants, and only at the highest levels did it reach a high enough concentration to turn something into a hero-level threat.
• All of this assumes a vaguely Earthlike setup, since Earth is the only planet known to have an actual biosphere, but informs how things might work elsewhere.
  • A planet near a Class O star has a greater energy density from its sunlight, and might be able to support enormous predators at the top of long food chains with a fraction of the territory one on Earth would need (assuming it survived long enough to develop those chains). One near a Class M star might struggle to support one trophic level even supplementing itself by breaking down the planet.
  • A world with magical energy inputs might work similarly to one running on chemoautotrophs. A dungeon with a place of power at the bottom might have such weird stuff in it because it's the equivalent of a hydrothermal vent: the ecosystem is self-sustaining, and largely self-contained, so its evolution is totally separate from anything in the outside world.[2]
  • If conservation of energy doesn't apply, all of this goes out the window. A species that can manage over-unity cannibalism needs no producers, and might itself be a producer for something else. Undead that need no food might survive for eons until destroyed.
  • A species that can at least partially consume magical energy from the environment (a thaumatovore?) might be at great risk of being hunted down for power components. Probably the bit that serves as the "mouth" or "stomach" for the magical energy. Or its analogous "fat reserves".
    • "Fat reserves" would be a good example for a consumable. The "mouth", "stomach", or "guts" might instead be used in constructing self-powering items.
  • Shadow life might form a shadow ecosystem, with its own parallel food chains or even parallel energy sources. Two or more separate "biospheres" might occupy the same planet, competing only for space.

Footnotes

1. Greek: self-feeding

2. Greek: other-feeding

3. A real-life example of this is DDT, which kills insects very well, but also weakens bird eggshells.

4. For example, deep-sea ecosystems usually depend on dead animals falling from shallower ocean, which is several levels removed.