History Main / IntroducedSpeciesCalamity

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* Malcolm from ''Film/JurassicPark'' posits that this will be the result of resurrecting dinosaurs.

[[folder:Film]]

* ''WesternAnimation/WreckItRalph'': When Ralph accidentally brings a cy-bug from the war game ''Hero's Duty'' to the much friendlier racing game ''Sugar Rush'', the cy-bug, with plentiful food and no-one to control its numbers, is quick to reproduce and infest the game.

%%** Played for tragedy in the case of the Krogan. Originally a pre-spaceflight species, the Krogan were technologically uplifted by the Salarians to serve as soldiers in the [[BugWar war against the Rachni]]. This is because the [[ExplosiveBreeder unique]] [[HealingFactor biology]] that allowed the Krogan to survive on their [[DeathWorld homeworld Tuchanka]] also made them an excellent counter to the numbers utilized by the Rachni, in addition to allowing the Krogan to survive the hostile environments of the Rachni worlds, which allowed the Citadel forces to invade them. Things only started to become a problem after the war concluded. As a reward for helping win the war, the Krogan were granted a number of colony worlds to settle. But this soon proved highly dangerous when the krogan began to breed out of control because these less-hostile worlds couldn't keep krogan numbers in check like their homeworld could, and being an uplifted species, the Krogan had no experience or desire to maintain their own populations. Numerous accounts exist of krogan colonists overwhelming the natural environments of the planets they were allowed to colonize, which forced them to expand further. To make matters worse, [[ProudWarriorRace the warrior culture of the Korgan]] meant that they soon began forcibly colonizing worlds that were already inhabited by other Citadel races, which inevitably led to rising tensions between the invading Krogan armies and the [[FictionalUnitedNations Citadel Council]]. This then inevitably led to a new galactic-scale war against the Korgan that would be even more destructive than the Rachni War. Oddly enough, this led to a repeat of the Rachni War, with the Citadel Council recruiting a brand-new species to act as a counter to their enemy. In this case, the newly contacted Turians, who have a similar culture to the Krogan but are [[SoldierVsWarrior more militaristic]]. Despite the help of the Turians, krogan numbers were simply too numerous to win the war conventionally. The war only ended when the Salarians developed a SterilityPlague known as the Genophage, which the Turians then weaponized to infect the entire Krogran race. After the war ended, the Krogan were banished to their homeworld and forced to live with a drastically reduced ability to reproduce as a result of the Genophage. This led to the Krogan doubling down on their warrior culture and turning into a demoralized DyingRace, reduced to constantly killing each other in a primitive clan system while squabbling over any female capable of consistently bearing young.%%Krogans are a sapient species capable of independent interstellar travel, qualification unclear.%%
%%** Vorcha are an accidental example of this: a primitive species that started out on the brutal planet of Heshtok, they were introduced to the rest of the galaxy when explorers landed on their homeworld, unwittingly giving the vorcha a chance to stow away. Aggressive, fast-healing, fast-breeding and short-lived, they flourished away from their homeworld - to the point that parties on [[WretchedHive Omega]] go out of their way to cull their numbers before they grow too numerous. Thanks to their aggressive streak, they're [[FantasticRacism popularly stereotyped as violent criminals and scavengers]], especially given that the Blood Pack exploits their breeding rates to employ them as shock troops.%%Vorcha are sapient%%

** Played for tragedy in the case of the Krogan. Originally a pre-spaceflight species, the Krogan were technologically uplifted by the Salarians to serve as soldiers in the [[BugWar war against the Rachni]]. This is because the [[ExplosiveBreeder unique]] [[HealingFactor biology]] that allowed the Krogan to survive on their [[DeathWorld homeworld Tuchanka]] also made them an excellent counter to the numbers utilized by the Rachni, in addition to allowing the Krogan to survive the hostile environments of the Rachni worlds, which allowed the Citadel forces to invade them. Things only started to become a problem after the war concluded. As a reward for helping win the war, the Krogan were granted a number of colony worlds to settle. But this soon proved highly dangerous when the krogan began to breed out of control because these less-hostile worlds couldn't keep krogan numbers in check like their homeworld could, and being an uplifted species, the Krogan had no experience or desire to maintain their own populations. Numerous accounts exist of krogan colonists overwhelming the natural environments of the planets they were allowed to colonize, which forced them to expand further. To make matters worse, [[ProudWarriorRace the warrior culture of the Korgan]] meant that they soon began forcibly colonizing worlds that were already inhabited by other Citadel races, which inevitably led to rising tensions between the invading Krogan armies and the [[FictionalUnitedNations Citadel Council]]. This then inevitably led to a new galactic-scale war against the Korgan that would be even more destructive than the Rachni War. Oddly enough, this led to a repeat of the Rachni War, with the Citadel Council recruiting a brand-new species to act as a counter to their enemy. In this case, the newly contacted Turians, who have a similar culture to the Krogan but are [[SoldierVsWarrior more militaristic]]. Despite the help of the Turians, krogan numbers were simply too numerous to win the war conventionally. The war only ended when the Salarians developed a SterilityPlague known as the Genophage, which the Turians then weaponized to infect the entire Krogran race. After the war ended, the Krogan were banished to their homeworld and forced to live with a drastically reduced ability to reproduce as a result of the Genophage. This led to the Krogan doubling down on their warrior culture and turning into a demoralized DyingRace, reduced to constantly killing each other in a primitive clan system while squabbling over any female capable of consistently bearing young.
** Vorcha are an accidental example of this: a primitive species that started out on the brutal planet of Heshtok, they were introduced to the rest of the galaxy when explorers landed on their homeworld, unwittingly giving the vorcha a chance to stow away. Aggressive, fast-healing, fast-breeding and short-lived, they flourished away from their homeworld - to the point that parties on [[WretchedHive Omega]] go out of their way to cull their numbers before they grow too numerous. Thanks to their aggressive streak, they're [[FantasticRacism popularly stereotyped as violent criminals and scavengers]], especially given that the Blood Pack exploits their breeding rates to employ them as shock troops.

** Played for tragedy in the case of the Krogan. Originally a pre-spaceflight species, the Krogan were technologically uplifted by the Salarians to serve as soldiers in the [[BugWar war against the Rachni]]. This is because the [[ExplosiveBreeder unique]] [[HealingFactor biology]] that allowed the Krogan to survive on their [[DeathWorld homeoworld Tuchanka]] also made them an excellent counter to the numbers utilized by the Rachni, in addition to allowing the Krogan to survive the hostile environments of the Rachni worlds, which allowed the Citadel forces to invade them. Things only started to become a problem after the war concluded. As a reward for helping win the war, the Krogan were granted a number of colony worlds to settle. But this soon proved highly dangerous when the krogan began to breed out of control because these less-hostile worlds couldn't keep krogan numbers in check like their homeworld could, and being an uplifted species, the Krogan had no experience or desire to maintain their own populations. Numerous accounts exist of krogan colonists overwhelming the natural environments of the planets they were allowed to colonize, which forced them to expand further. To make matters worse, [[ProudWarriorRace the warrior culture of the Korgan]] meant that they soon began forcibly colonizing worlds that were already inhabited by other Citadel races, which inevitably led to rising tensions between the invading Krogan armies and the [[FictionalUnitedNations Citadel Council]]. This then inevitably led to a new galactic-scale war against the Korgan that would be even more destructive than the Rachni War. Oddly enough, this led to a repeat of the Rachni War, with the Citadel Council recruiting a brand-new species to act as a counter to their enemy. In this case, the newly contacted Turians, who have a similar culture to the Krogan but are [[SoldierVsWarrior more militaristic]]. Despite the help of the Turians, krogan numbers were simply too numerous to win the war conventionally. The war only ended when the Salarians developed a SterilityPlague known as the Genophage, which the Turians then weaponized to infect the entire Krogran race. After the war ended, the Krogan were banished to their homeworld and forced to live with a drastically reduced ability to reproduce as a result of the Genophage. This led to the Krogan doubling down on their warrior culture and turning into a demoralized DyingRace, reduced to constantly killing each other in a primitive clan system while squabbling over any female capable of consistently bearing young.

** Played for tragedy in the case of the krogan. Originally a pre-spaceflight species, the krogan were technologically uplifted by the salarians to serve as soldiers in the [[BugWar war against the rachni]]. This is because the [[ExplosiveBreeder unique]] [[HealingFactor biology]] that allowed the krogan to survive on their [[DeathWorld homeworld Tuchanka]] also made them an excellent counter to the numbers utilized by the rachni, in addition to allowing the krogan to survive the hostile environments of the rachni worlds, which allowed the Citadel forces to invade them. Things only started to become a problem after the war concluded. As a reward for helping win the war, the krogan were granted a number of colony worlds to settle. But this soon proved highly dangerous when the krogan began to breed out of control because these less-hostile worlds couldn't keep krogan numbers in check like their homeworld could, and being an uplifted species, the krogan had no experience or desire to maintain their own populations. Numerous accounts exist of krogan colonists overwhelming the natural environments of the planets they were allowed to colonize, which forced them to expand further. To make matters worse, [[ProudWarriorRace the warrior culture of the krogan]] meant that they soon began forcibly colonizing worlds that were already inhabited by other Citadel races, which inevitably led to rising tensions between the invading krogan armies and the [[FictionalUnitedNations Citadel Council]]. This then inevitably led to a new galactic-scale war against the krogan that would be even more destructive than the Rachni War. Oddly enough, this led to a repeat of the Rachni War, with the Citadel Council recruiting a brand-new species to act as a counter to their enemy. In this case, the newly contacted turians, who have a similar culture to the krogan but are [[SoldierVsWarrior more organized]]. Despite the help of the turians, krogan numbers were simply too numerous to win the war conventionally. The war only ended when the salarians developed a SterilityPlague known as the Genophage, which the turians then weaponized to infect the entire krogan race. After the war ended, the krogan were banished to their homeworld and forced to live with a drastically reduced ability to reproduce as a result of the Genophage. This led to the krogan doubling down on their warrior culture and turning into a demoralized DyingRace, reduced to constantly killing each other in a primitive clan system while squabbling over any female capable of consistently bearing young.

** Played for tragedy in the case of the Krogan. Originally a pre-spaceflight species, the Krogan were technologically uplifted by the Salarians to serve as soldiers in the [[BugWar war against the Rachni]]. This is because the [[ExplosiveBreeder unique]] [[HealingFactor biology]] that allowed the Krogan to survive on their [[DeathWorld homeoworld Tuchanka]] also made them an excellent counter to the numbers utilized by the Rachni, in addition to allowing the Krogan to survive the hostile environments of the Rachni worlds, which allowed the Citadel forces to invade them. Things only started to become a problem after the war concluded. As a reward for helping win the war, the Krogan were granted a number of colony worlds to settle. But this soon proved highly dangerous when the krogan began to breed out of control because these less-hostile worlds couldn't keep krogan numbers in check like their homeworld could, and being an uplifted species, the Krogan had no experience or desire to maintain their own populations. Numerous accounts exist of krogan colonists overwhelming the natural environments of the planets they were allowed to colonize, which forced them to expand further. To make matters worse, [[ProudWarriorRace the warrior culture of the Korgan]] meant that they soon began forcibly colonizing worlds that were already inhabited by other Citadel races, which inevitably led to rising tensions between the invading Krogan armies and the [[FictionalUnitedNations Citadel Council]]. This then inevitably led to a new galactic-scale war against the Korgan that would be even more destructive than the Rachni War. Oddly enough, this led to a repeat of the Rachni War, with the Citadel Council recruiting a brand-new species to act as a counter to their enemy. In this case, the newly contacted Turians, who have a similar culture to the Krogan but are [[SoldierVsWarrior more militaristic]]. Despite the help of the Turians, krogan numbers were simply too numerous to win the war conventionally. The war only ended when the Salarians developed a SterilityPlague known as the Genophage, which the Turians then weaponized to infect the entire Krogran race. After the war ended, the Krogan were banished to their homeworld and forced to live with a drastically reduced ability to reproduce as a result of the Genophage. This led to the Krogan doubling down on their warrior culture and turning into a demoralized DyingRace, reduced to constantly killing each other in a primitive clan system while squabbling over any female capable of consistently bearing young.

** Played for tragedy in the case of the Krogan. Originally a pre-spaceflight species, the Krogan were technologically uplifted by the Salarians to serve as a soldiers in the [[BugWar war against the Rachni]]. This is because the [[ExplosiveBreeder unique]] [[HealingFactor biology]] that allowed the Krogan to survive on their [[DeathWorld homeoworld Tuchanka]], also made them an excellent counter to the numbers utilized by the Rachni, in addition to allowing the Krogan to survive the hostile environments of the Rachni worlds, allowing the Citadel forces to invade them. Things only started to become a problem after the war concluded. As a reward for helping win the war, the Krogan were granted a number of colony worlds to settle. But this soon proved highly dangerous when the krogan began to breed out of control because these less-hostile worlds couldn't keep krogan numbers in check like their homeworld could, and being an uplifted species, the Krogan had no experience or desire to maintain their own populations. Numerous accounts exist of krogans overwhelming the natural environments of the planets they were allowed to colonize, eventually forcing them to expand further. To make matters worse, [[ProudWarriorRace the warrior culture of the Korgan]] meant that they soon began colonizing worlds that were already inhabited by other Citadel races, which inevitably led to rising tensions between the invading Krogan armies and the [[FictionalUnitedNations Citadel Council]]. This then inevitably led to a new galactic scale war against the Korgan that would even more destructive than the Rachni War, only ending when the Salarians and another newly contacted species, [[ProudSoldierRace the Turians]], infected the Krogan with a SterilityPlague known as the Genophage. After the war ended, the Krogan were banished to their homeworld and forced to live with a drastically reduced ability to reproduce. This led to the Krogan doubling down on their warrior culture and turning into a demoralized DyingRace, reduced to constantly killing each other in a primitive clan system, while squabbling over any female capable of consistently bearing live young,

** Played for tragedy in the case of the krogan. Deliberately uplifted to serve as a trump card in the war against the rachni, things started going wrong once the war was won: the [[ExplosiveBreeder traits]] that had [[HadToBeSharp allowed the krogan to survive]] on their home world of [[DeathWorld Tuchanka]] soon proved highly dangerous once they ended up on less-hostile worlds: numerous accounts exist of krogan overwhelming the natural environments of the planets they were allowed to colonize, eventually forcing them to expand further. Worse still, krogan are not only [[ItCanThink intelligent beings]] but also a ProudWarriorRace, so it didn't take long for tensions between an overpopulated krogan army and a stubborn galactic government to erupt into conflict. Consequently, a new war started - one that only ended when the salarians and the turians infected the krogan with the [[SterilityPlague Genophage]]. Krogan still exist by the start of the series, but as a demoralized DyingRace reduced to squabbling over any female capable of consistently bearing live young.

* ''Blog/HamstersParadise'': When the isolated continent of Borealia collides with the continent of Nodera multiple species were able to cross over the connecting landbridge. The most devastating of these was the Borelian saberleaf grass crossing into Nodera, the plant incorporated silica into its blades which makes it [[TheHedgeOfThorns razor sharp]] and too dangerous for herbivores to eat or even just walk through and its prolific breeding outcompeted native grasses and drove several species of Noderan grazers into extinction or forced them into other habitats. However, an [[InvertedTrope inversion]] of this trope happened when the ungulope, another native of Borealia, entered Nodera, their mouths, throats and stomachs were designed to safety consume saberleaf and when they fed on it they reduced its numbers and allowed the native grass and herbivores to recover.
* ''Website/{{Serina}}'': The Kyran Islands were an isolated group of islands that where home to various species of small burrowing birds called snuffles that hid from large predatory birds by hiding underground, but when the islands became connected to the mainland it allowed the small, mammal-like tribbetheres to enter the region, and unlike the native flightless birds they were able to follow the snuffles into their homes and eventually hunt them into extinction.

A type of SnowballingThreat.

** Even the dingo, an Australian icon, is one of these, brought to Australia by the first humans to settle there. Competition with dingos, as well as diseases transmitted from them, may have resulted in the extinction of the two largest carnivorous marsupials on the Australian mainland, the thylacine/Tasmanian tiger and purinina/Tasmanian devil, although both species survived on the island of Tasmania until the thylacine was wiped out in 1936.

* ''WebOriginal/CodexInversus'': The Valley of Delights was infested by a local pest species known as manticorats, known for their quick breeding and propensity for devouring magic ingredients and spells alike. To control them, the wizard Alamandry created an artificial species known as chimericats, provided with keen intelligence, blade-tipped tails and intense territoriality to control the pests. The chimericats did their job exceptionally well but, once the manticorats were reduced to small footholds, the voracious and aggressive felines began to prey on other wildlife just as efficiently, then pets, then livestock, and when a pack claims a house or a wizard tower as its territory it becomes an active danger instead of a simple pest. The Valley is now dealing with a chimericat infestation as ingrained and much more problematic than the manticorat one, and Alamandry is trying to create a new, larger predator species to control them. Second time's the charm, surely.

* ''WebOriginal/HamstersParadise'': When the isolated continent of Borealia collides with the continent of Nodera multiple species were able to cross over the connecting landbridge. The most devastating of these was the Borelian saberleaf grass crossing into Nodera, the plant incorporated silica into its blades which makes it [[TheHedgeOfThorns razor sharp]] and too dangerous for herbivores to eat or even just walk through and its prolific breeding outcompeted native grasses and drove several species of Noderan grazers into extinction or forced them into other habitats. However, an [[InvertedTrope inversion]] of this trope happened when the ungulope, another native of Borealia, entered Nodera, their mouths, throats and stomachs were designed to safety consume saberleaf and when they fed on it they reduced its numbers and allowed the native grass and herbivores to recover.

* ''WebOriginal/{{Serina}}'': The Kyran Islands were an isolated group of islands that where home to various species of small burrowing birds called snuffles that hid from large predatory birds by hiding underground, but when the islands became connected to the mainland it allowed the small, mammal-like tribbetheres to enter the region, and unlike the native flightless birds they were able to follow the snuffles into their homes and eventually hunt them into extinction.

** Played for tragedy in the case of the Krogan. Deliberately uplifted to serve as a trump card in the war against the Rachni, things started going wrong once the war was won: the [[ExplosiveBreeder traits]] that had [[HadToBeSharp allowed the Krogan to survive]] on their home world of [[DeathWorld Tuchanka]] soon proved highly dangerous once they ended up on less-hostile worlds: numerous accounts exist of Krogan overwhelming the natural environments of the planets they were allowed to colonize, eventually forcing them to expand further. Worse still, Krogan are not only [[ItCanThink intelligent beings]] but also a ProudWarriorRace, so it didn't take long for tensions between an overpopulated Krogan army and a stubborn galactic government to erupt into conflict. Consequently, a new war started - one that only ended when the Salarians and the Turians infected the Krogan with the [[SterilityPlague Genophage]]. Krogan still exist by the start of the series, but as a demoralized DyingRace reduced to squabbling over any female capable of consistently bearing live young.
** Vorcha are an accidental example of this: a primitive species that started out on the brutal planet of Heshtok, they were introduced to the rest of the galaxy when explorers landed on their homeworld, unwittingly giving the Vorcha a chance to stow away. Aggressive, fast-healing, fast-breeding and short-lived, they flourished away from their homeworld - to the point that parties on [[WretchedHive Omega]] go out of their way to cull their numbers before they grow too numerous. Thanks to their aggressive streak, they're [[FantasticRacism popularly stereotyped as violent criminals and scavengers]], especially given that the Blood Pack exploits their breeding rates to employ them as shock troops.

** ''VideoGame/PokemonScarletAndViolet'': [[spoiler: TheProfessor's TimeMachine created [[ParadoxPerson Paradox Pokémon]], which are supposedly past/future versions of contemporary {{mons}} brought to the current day and absurdly powerful (if you see a robot Delibird when battling online, forfeit immediately). The PlayerCharacter has to shut down the machine in order to prevent them from overrunning the region, displacing the native {{mons}}, and potentially destroying their civilization.]]

* In many cases it was predation by introduced rats, dogs, and pigs, not hunting as is commonly assumed, that led to the extinction of the dodo and many other flightless birds native to islands. Special mention goes to the Stephen's Island Wren of New Zealand, which was supposedly wiped out in the space of a few weeks by a lighthouse keeper's cat.

* Australia has some of the most infamous examples of introduced pests, many of which are so adaptable that they have proved a serious threat to Australian biodiversity, ecological stability, and in some cases, even to the economy in such an isolated ecosystem. [[ProperlyParanoid That's why the country takes biosecurity so seriously]].

* ''WesternAnimation/ScoobyDooMysteryIncorporated'': In [[Recap/ScoobyDooMysteryIncS2E17TheHorribleHerd "The Horrible Herd"]], Professor Pericles invents a herd of skull cattle that are a [[MixAndMatchCritters mutant combination of cow, bee and piranha]] with the intent of them devouring all of Crystal Cove. At the very end, the gang lead the herd into the ocean hoping to drown them, but forget that they're part piranha, so they can swim away. While we never see the consequences, they know they messed up.