Ecosystem Simulation · Game Mechanic Compendium

Definition

Ecosystem simulation is an inhabitants system driven autonomously: creatures need food, hunt one another and fight over ground on their own rules, so the predators, prey and populations the player meets follow from a running food chain. NPC schedules differs: its characters keep a timetable, where these creatures act from hunger. Upkeep holds a recurring food cost and hit points the damage creatures do to one another; the archetype is the loop in which one creature’s meal is another’s loss.

How the parts interact

The stored state is which creatures live, how many, and how hungry they are. In Evolution food cards played from hand set the plant food each round. A carnivore must attack a species of smaller body size, cutting its population by one and taking meat equal to that body size, and any population left hungry when feeding ends is lost. In Rain World the slugcat is both predator and prey and must eat enough before the rain to hibernate without starving; the more it eats one day, the less food there is the next. Its developers say creatures off screen keep hunting and fighting over territory.

In Monster Hunter the chain reaches the hunt. A preview of Monster Hunter: World saw an Anjanath eat a smaller creature whole, then fight a Rathalos unscripted and retreat when losing, while the hunters cut off its tail. In Monster Hunter Wilds the Fallow sends hungry predators roaming, an Inclemency brings the apex monster, and Plenty follows; a hunter can lure a stronger apex monster to a herd so the monsters wear each other down.

Variations

Player-run species (Evolution): each species belongs to a player, who chooses its traits and prey; starvation and predation apply by rule.
Off-screen simulation (Rain World): creatures keep hunting beyond the player’s view.
Turf fights (Monster Hunter: World, Monster Hunter Wilds): large monsters fight each other, and hunters exploit or provoke it.
Seasonal ecology and herds (Monster Hunter Wilds): a cycle sets how hungry creatures are and when the apex appears, and herds follow a leader and scatter in panic.

Components

Upkeep, a recurring food cost whose failure removes population, recurs in the board game and Rain World. Hit points and boss encounters recur in the Monster Hunter examples, where large monsters damage one another and the hunt’s target is an individually designed monster; World adds hit location. Evolution adds hand management and victory points, and Rain World’s rain clock is a progress clock bounding each foraging cycle. A creature’s hunger, its choice of prey, population growth and herd panic have no catalog mechanic. No tabletop role-playing example is cited.

History and provenance

The earliest documented use cited is SimLife (1992), described in a review of that year as simulating organisms, with predator and prey scenarios and a food web graph. SimEarth (1990) and earlier simulations remain unsurveyed. Ultima Online planned an ecology on a resource bank, in which hungry wolves followed the rabbits players hunted; Raph Koster writes that it worked in the alpha test and was removed during beta. Evolution (2014), grown from a teaching tool by the biologist Dmitry Knorre, carried the food chain to the board. Rain World (2017) and the Monster Hunter games of 2018 and 2025 built play around creatures that hunt each other.

Notable examples

Notable examples, in chronological order. Notes describe how the system works in each game; the components are the mechanics it combines there and the parts its own working parts; the latest reference is a widely played game from 2020 or later.
Game	Year	Medium	Parts	Components	How the system works
Evolution Dominic Crapuchettes, Dmitry Knorre and Sergey Machin (North Star Games)	2014	Board & card	Agent needs, Population change	Hand Management, Upkeep and Attrition, Victory Points	Cards played from hand set the plant food at the Watering Hole each round. A carnivore must attack a species of smaller body size, cutting its population by one and taking meat equal to its body size, and every population left hungry is lost. Food eaten and surviving population score.
Rain World Videocult	2017	Video	Drain, Agent needs, Forecast	Upkeep and Attrition, Progress Clocks	The slugcat sits in the middle of a food chain, both predator and prey, and must eat enough before the rain clock runs out to hibernate without starving; the more it eats one day, the less food there is the next. Creatures off screen keep hunting and fighting over territory.
Monster Hunter: World Capcom	2018	Video	Routines, Agent needs	Boss Encounters, Hit Points, Hit Location	An E3 2017 preview saw an Anjanath eat a smaller creature whole and then fight a Rathalos in an unscripted clash, retreating when it was losing, while the hunters shot off its tail for materials.
Monster Hunter Wilds Latest Capcom	2025	Video	Conditional spawn, Agent needs, Population change	Boss Encounters, Hit Points	In the Fallow hungry predators roam for food and herds grow aggressive, an Inclemency brings the area's apex monster, and Plenty follows. The director says a hunter can lure a stronger apex monster to a herd so that the monsters fight and wear each other down.

Provenance

Earliest documented use: SimLife (1992), video. Confidence: low. The earliest documented use cited is SimLife (Maxis), described in a review of October 1992 as simulating the behaviour and activities of organisms, with scenarios on the dynamics of a predator and prey system and a food web graph. SimEarth (1990) and earlier simulations remain unsurveyed, and the source is a user review, so confidence is low. Ultima Online's planned ecology ran in its alpha test and was removed before release.

Sources

Dominic Crapuchettes and David Lipman (North Star Games). Evolution rulebook (web edition). Rulebook Phase 2: Select Food, p. 4; Phase 4: Reveal Food and Phase 5: Feeding, p. 6; Feeding Carnivores and End of Feeding, p. 7; Extinction, p. 8. Accessed 2026-10-30. Food cards from hand setting the plant food, carnivores attacking smaller species and taking meat, hungry population lost, extinction, scoring by food and population, and the game's origin as a teaching tool by Dmitry Knorre.
Rick Russell, comp.sys.mac.games. (1992). SimLife review. Article Accessed 2026-10-30. SimLife simulating the behaviour and activities of organisms, predator and prey scenarios, the Food Web graph, gestation, offspring and mutation settings; dated 8 October 1992.
Beth C. Fishkind (COMPUTE!). (1993). SimLife. Article Issue 155, August 1993, p. 93. Accessed 2026-10-30. Building an ecosystem and testing it with disasters, and species that go extinct.
Raph Koster. (2006). UO's resource system, part 2. Website Accessed 2026-10-30. Rabbits eating grass, meat-eaters spawned from a surplus of meat, hungry wolves when players hunt the rabbits, a dragon's search for meat reaching a village, the resource bank, the ecology working in alpha, and creatures put to sleep when no player was near.
Raph Koster. Did players destroy the UO ecology?. Website Accessed 2026-10-30. The ecology in the alpha test and removed during beta, its AI disabled for the cost of radial searches and pathfinding.
Chris Priestman (Game Developer), interviewing Joar Jakobsson and James Therrien. (2017). Crafting the complex, chaotic ecosystem of Rain World. Interview Accessed 2026-10-30. The slugcat as predator and prey, eating enough to hibernate without starving, less food the day after, the rain clock, and creatures hunting and fighting over territory off screen.
Videocult. Rain World (Steam store page). Website Accessed 2026-10-30. Hunting food to survive among bigger creatures with the same plan, and the release date of 28 March 2017.
Cody Perez (GameRevolution). (2017). Monster Hunter: World's Living Ecosystem Creates Unexpected Gameplay [E3 2017 Preview]. Article Accessed 2026-10-30. An Anjanath eating prey whole, its unscripted fight with a Rathalos and retreat, and the hunters severing its tail while it was distracted.
Joseph Bustos (Capcom USA), PlayStation Blog. (2024). Monster Hunter Wilds: all the news from Gamescom Opening Night Live. Article Accessed 2026-10-30. Fallow, Inclemency and Plenty, hungry predators and aggressive herds in the Fallow, and the apex monster at the top of each locale's ecosystem.
Joseph Bustos (Capcom USA), PlayStation Blog. (2024). Monster Hunter Wilds: new gameplay details from today's State of Play. Article Accessed 2026-10-30. Herds and packs that interact, monsters acting independently to survive, and monsters changing with the environment.
Alexander Mehrwald (MeinMMO), interviewing Yuya Tokuda. (2025). Ich habe die Entwickler von Monster Hunter Wilds zu einem Feature befragt, das noch total unterschätzt wird. Interview Accessed 2026-10-30. Tokuda on herds with leaders that panic and scatter, and on luring a stronger apex monster to a herd so the monsters fight and wear each other down.

Cite this entry

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Updated: 2026-10-30
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West, James, Jr. (2026). "Ecosystem Simulation." Game Mechanic Compendium, updated 2026-10-30. http://localhost:4321/systems/ecosystem-simulation

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