Always a Bigger Fish



"(The heroes' submarine is grabbed by a huge Opee Sea Killer) Jar Jar: Big Gooba fish!!!! HUGE TEETH!!!! (The Opee Sea Killer is grabbed by the much larger Sando Aqua Monster) Qui-Gon Jinn: There's always a bigger fish."

- Star Wars Episode I: The Phantom Menace

The more primal equivalent of Bad Guys Do the Dirty Work.

Our heroes are cornered or trapped by one scary thing or group, only to be saved by the other, bigger, scarier thing or group. Sometimes the "savior" has been introduced earlier in the plot, making this an instance of Chekhov's Gun.

If the "savior" was previously the main antagonist, this may set up an unusual reaction in the viewer, who notes how his feelings about that antagonist are changed in this scene. The characters may notice the same; they may say, "I never thought I'd be so happy to see you!".

Generally the "savior" is not actively trying to save the protagonists. He's just there. And hungry.

Summon Bigger Fish is a Sub-Trope. May result when the hero asking "Why Isn't It Attacking?" has the bigger fish behind him.

Common form of Deus Ex Machina. See also Colliding Criminal Conspiracies when the "Bigger Fish" arrives early and threatens heroes and villains equally.

Compare to Save the Villain, Did You Just Punch Out Cthulhu?, Exit, Pursued by a Bear, Self-Disposing Villain, and Eviler Than Thou. If it's a videogame, and you have to also fight the bigger fish, it's a Bait and Switch Boss. For actual bigger fish (and other things) see Sea Monster.

Advertising
"Aussie: No. No crocodiles, mate. American: (dives in) Aussie: Sharks ate 'em."
 * There is an Australian advertisement where an American tourist asks locals if there are any crocodiles in the water.

Anime & Manga

 * In Monster, Nina is saved from Professor Geidlitz by Johan.
 * What makes this better is that they were using her as bait to lure Johan in to convince him to lead their group and make "the master race" dominant once again, seeing him as the next Hitler. Anna tried to warn them that Johan didn't care about their cause or any cause. They discover too late that she's correct.
 * Used to great effect during the Batman Cold Open of the One Piece movie Strong World. Luffy is pursued by a giant alligator, which is defeated by a Forest Octopus, which is in turn defeated by a giant preying mantis, which is itself defeated by a gorilla-bear, only to have that thing finished off by Luffy himself once he gets sick of this.
 * A heroic variant in the Rurouni Kenshin episode, "Birth of a Child Swordsman": Yahiko is being chased by the gang of thugs he's been dealing with the entire episode. He leads them into an narrow alleyway where he can fight them one-on-one, but the thugs wise up and approach en masse, knives drawn. Then the thugs look up and notice Kenshin and Sanosuke on the wall behind Yahiko (either of whom would've been enough to make the thugs pause). Most of the thugs flee, but the leader wants to settle the score with Yahiko. He ends up giving Yahiko his first victory in a real fight.
 * A(n even more) sinister variant in Puella Magi Madoka Magica: The only way to defeat The Walpurgis Night is.
 * In the finale.
 * Dragonball Z: Frieza and his even stronger father are coming. This could mean the end of all life on Earth. As soon as they arrive, a person we've never seen before shows up and cuts them both in half with a sword.

Comics

 * The climax of Bone is an interesting double-helping of this trope:.
 * In an early sunday strip of Calvin and Hobbes, Calvin shrinks down suddenly to the size of a bug from the perspective of other bugs. A fly tries to step on him until a frog eats it.
 * One Sherman's Lagoon comic has a progression of Bigger Fish eating each other. When Sherman, a Great White Shark, shows up to eat the third, another fish protests, "You're going out of turn. I eat that guy, then you eat me."
 * Occurs in Nth Man the Ultimate Ninja when Reality Warper Alfie O'Meagan is waiting for a cosmic being called M'Gubgub. He barely avoids being stepped on by a massive alien who dwarfs the planet and proceeds to praise M'Gubgub... only for the alien to run away in a panic, as the galaxy-dwarfing M'Gubgub arrives.
 * This strip by Argentinian cartoonist Quino (the text translates as "Death to the big guy"). Also this one.
 * And here's an inversion.

Films -- Animation

 * Humorously meddled with in The SpongeBob SquarePants Movie when Dennis the Bounty Hunter finally catches up to SpongeBob and Patrick. Patrick even yells out "Bigger Boot!"
 * Played less straight earlier in the film when the anglerfish that ate their car is itself eaten by an enormous deep-sea eel. SpongeBob and Patrick's shocked expressions are priceless.
 * In Help! I'm a Fish, the main characters are collecting ingredients to make a potion to turn them back into humans, but run into trouble getting an octopus to squirt ink, as it is much bigger than they are and thus just grabs them. It does eventually squirt ink and swim away, which Fly attributes to their screaming scaring it off, but was really because of the great white shark approaching...
 * In the "Mickey and the Beanstalk" segment of Fun and Fancy Free, when Mickey Mouse, Donald Duck, and Goofy arrive at Willie the Giant's castle after their house is carried upwards by a beanstalk, a giant dragonfly swoops down and tries to attack the three, but a giant catfish living in Willie's moat jumps up and eats the dragonfly.
 * In The Sword in the Stone, when Goldfish Arthur "Wart" Pendragon is chased by a pike living in the moat he is suddenly lifted out of the water by Archimedes, who thinks that Wart is his dinner. Before Archimedes captures Wart he scares off the pike.

Films -- Live-Action

 * In Star Wars: The Phantom Menace, as Qui-Gon, Obi-Wan and Jar Jar travel in a sub through the watery core of Naboo, this happens twice in a row for a total of 4 progressively bigger fish. (Although the 2nd and 4th monsters are the same individual.) Riff Trax parodies this line, noting that for it to be true, a fish that could swallow the cosmos would need to exist. And an even bigger one to swallow that fish too, and so on, ad infinitum.
 * The heroes of Jurassic Park are about to get eaten by velociraptors, but the T. rex shows up to save the day.
 * In Jurassic Park 3, the heroes run from a Spinosaurus straight into the hunting grounds of a T.Rex. The spinosaur, but later begins chasing them again.
 * Speaking of You Shall Not Pass, in The Fellowship of the Ring, the eponymous gang of nine are in the deeps of Moria surrounded by countless goblins... until the goblins themselves start running for their very lives. Guess who had woken up and was really mad?
 * The 2009 Star Trek reboot has this happen when Kirk is abandoned on an ice planet. He gets chased by some sort of space-polar-bear. After a while another massive creature smashes through the ice and eats it. Then promptly throws the large slab of meat it just caught to chase down Kirk.
 * In Peter Jackson's King Kong, the heroine hides from a huge carnivorous lizard in a hollow log, and it tears at the wood to try to get her. Suddenly it stops, and she seems safe... until half the same lizard is seen dangling from the jaws of a ginormous V. rex, which just bit it in two.
 * Kong himself is a near constant example of this trope in the first half of the movie, as he repeatedly kills a number of animals that are trying to eat Anne Darrow.
 * In the first Alien vs. Predator movie, a Predator attacks Alexa, but is killed by an Alien.
 * In the Brendan Frasier version of Journey to the Center of the Earth, the heroes are saved from vicious coelacanth-type fish by plesiosaur-type sea monsters.
 * In Avatar, Jake faces down a huge, charging rhino-like titanothere. When it stops and retreats, he thinks he's won, only to have to run from what really scared it off: the bigger and nastier-looking carnivorous thanator that was creeping up behind him.
 * Averted in the film GMK. Actually Baragon is never attacked by the JDSF, as the Cabinet never actually takes action. In this instance Godzilla is still the Bigger Fish. Baragon goes straight to battle with him. Baragon is the hero, but nowhere near being the bigger fish.
 * Played straight in Godzilla VS Mechagodzilla II. Several members of the JSDF are attacked by Rodan as they try to take an egg from a nest. And, then, Godzilla (who is larger than Rodan) shows up and attacks both the JSDF and Rodan.
 * Subverted in The Colour of Magic, where a sinking pirate ship is devoured by a sea monster the size of a village... which shortly washes up dead on an island, as the smaller fish it swallowed along with the ship just happened to be the Luggage. Which kicked it to death from the inside.
 * Rodan. The miners are attacked by giant insects called the Meganula...That is, until the baby Rodan started hatching and began devouring the Meganula, attacking the miners, and escaping into the city.
 * In Lake Placid, the protagonists are arguing near the lakeside when a bear appears and attacks them. Then the crocodile unexpectedly pops out of the water and drags the bear in by its leg.
 * In the beginning of Sharktopus, a beach girl is attacked by a shark while swimming off the shoreline, but the Sharktopus saves her by devouring it.

Literature
"So nat'ralists observe, a flea Hath smaller fleas that on him prey, And these have smaller fleas that bite 'em, And so proceed ad infinitum: Thus ev'ry Poet in his Kind, Is bit by him that comes behind."
 * Flipped on its head in On Poetry by Jonathan Swift:

"Once he tried to feed all the animals in all the world in one day, but when the food was ready an Animal came out of the deep sea and ate it up in three mouthfuls. Suleiman-bin-Daoud was very surprised and said, "O Animal, who are you?" And the Animal said, "O King, live for ever! I am the smallest of thirty thousand brothers, and our home is at the bottom of the sea. We heard that you were going to feed all the animals in all the world, and my brothers sent me to ask when dinner would be ready.""
 * In Watership Down, after Hazel and Co. are attacked by General Woundwort, a massive dog is led into General Woundwort's forces, who naturally run. General Woundwort himself stays to beat up the dog. It’s worth noting that most of the characters are non-anthropomorphic rabbits, with the exception of Kehaar the seagull.
 * It's also worth mentioning that they Never Found the Body.
 * Well, they wouldn't, would they? Bigger Fish are often Hungrier Fish also.
 * Subverted in Tuf Voyaging. Wild Card Rica Dawnstar has Tuf outgunned and at her mercy, and refuses to believe him when he tries to point out the T. rex creeping up behind her. It looks like this trope will kick in...then it turns out she was toying with Tuf, and had the Phlebotinium to control the T. rex all along.
 * In Cain's Last Stand, the schola and PDF are completely swamped by the forces of Chaos. They've fallen back to the secret facility containing the Shadowlight, and are about to be overwhelmed when the Necrons decide to show up. They butcher the forces of Chaos pretty handily, giving Ciaphas Cain and company an opportunity to evacuate.
 * Alan Dean Foster loves this trope, especially as an excuse to show off his weird alien ecologies.
 * In Drowning World, characters menaced by a branch-clambering maccaluca are saved when it's snapped up by a vuniwai leaping up from the water.
 * Mid-Flinx is essentially one long string of Bigger Fish: Flinx's initial human pursuers are killed and supplanted by AAnn pursuers, and both groups of enemies are gradually picked off by one bizarre jungle predator after another.
 * It's played with in For Love Of Mother-Not when the penestral (roughly speaking, a pike that's 50 feet long) that attacks the bad guys doesn't save the heroes from them (it eats their boat, but the real villains has just escaped onto a flyer). The fisherwoman escorting Flinx scoffs at its size, pointing out that it wasn't terribly big for a penestral, and that the penestral is only a mid-range predator anyway. She offers to take Flinx fishing for oboweir sometime, and when he asks the inevitable "What's an oboweir?", her reply is "A fish that eats penestral."
 * In Casino Royale (book and movie), Bond is rescued from Le Chiffre when Le Chiffre's own superiors (SMERSH or QUANTUM, depending on the source) assassinate him.
 * In Book Three of Percy Jackson and The Olympians, a quad of undead warriors who had been attacking the heroes was chased off by the Erymanthian Boar.
 * A couple of times in The Dresden Files. In Proven Guilty, Harry has just and they've started fighting... Only for the bad guys to end up running away as fast as possible when the book's actual Big Bad shows up. Small Favor also has a sequence where Harry's trying to get away from a Fallen Angel, only for  to show up and take out the guy without even trying.
 * Used in Nightingale's Lament, when a limo Taylor is riding in is about to be attacked by a predator camouflaged as another car. Before it can do any damage, the critter is picked up and carried off by something HUGE with talons and wings. Possibly a subversion, as the limo might've been able to hold off the car-mimicking monster with its built-in defenses.
 * In the 11th book of A Series of Unfortunate Events, the Baudelaire orphans are in a submarine which is . However, when a mysterious question mark appears on the radar, everyone is scared, including . To make matters worse/better, the author never says just what the question mark was.
 * In Rudyard Kipling's "The Butterfly That Stamped" in his Just So Stories, the King Solomon's attempt to show off goes awry:


 * The Empire plays this role at the end of Shadows of the Empire, just as it looks like the rebels are about to be obliterated by Xizor's forces.
 * In Harry Potter, Harry and Hermione are surrounded by an angry mob of centaurs. Just as the situation is looking rather grim, a giant shows up, scattering the herd and chasing them into the forest. Hermione, characteristically, is worried about the centaurs....
 * In Robert E. Howard's The Scarlet Citadel, Conan the Barbarian, as Dude in Distress, is menaced by a snake, which is scared away by a man coming to kill Conan for killing his brother. The snake eats that man. (The keys that he taunted Conan with land at Conan's feet.)
 * In Peter Benchley's "Beast", the tititular giant squid is moments from finishing the remaining characters when it is attacked, killed, and presumably eaten by an equally massive sperm whale.
 * In 100 Great Science Fiction Short Short Stories, there's a story by Martin Gardner called "Thang," in which the titular being started eating the solar system but was interrupted by an even larger being scooping him up and swallowing him. "For there are other gods than Thang."
 * In the third book of Robin Hobb's Liveship Traders trilogy, Bingtown, the town in which much of the action takes place, is being completely overrun by the Chalcedonians... when the last of the ancient race of dragons wakes from her unexpectedly lengthy slumber, and goes looking in Bingtown for those responsible for her awakening. The Chalcedonians fire arrows at her in terror, and in response, she effortlessly kills them all.
 * The Featherbedders by Frank Herbert is about shapeshifting aliens who infiltrate and subvert other civilized species, having a trouble on Earth. Let's just say one of them gets to quote Swift (above).

Live-Action TV

 * Lost season 4 is all over this trope. One group of Losties hides from the freighties in the Others' Barracks. Later, a group cornered in a house are able to leave because the smoke monster (the series' original antagonist) attacks the bad guys. In the finale, when the Others showed up, fans at TWoP commented that they felt like the cavalry had arrived, quite a sharp contrast to the Others' first appearance in "Exodus Part 2".
 * Primeval Episode 6 features a scene in which Nick is rescued from a Future Predator when said predator is attacked by a Gorgonopsid.
 * Episode 3 features Nick being attacked by a mosasaur, only to have said mosasaur eaten by an even larger mosasaur right before it's about to chomp down on him.
 * At least once per season, Buffy the Vampire Slayer featured a scene in which some minor vampiric menace (who is convinced he's the Monster of the Week, or even Big Bad) shows up to kill Buffy just in time to get eaten by the true Monster of the Week.
 * One of the animation segues in an episode of Monty Python's Flying Circus has a section involving people being squashed on the streets by "killer cars", which were destroyed by a gigantic building-swallowing Siamese Cat, which was then killed by a several-hundred-foot-tall disembodied hand... and then it transitions into something else completely different.
 * Bored to Death: Our protagonist is saved from a scary murderous thug by driving into the back of a police car. While high.
 * The Mystery Science Theater 3000 episode King Dinosaur features two astronauts trapped in a cave by a Tyrannosaurus Rex that is actually an iguana. The arrival of a baby alligator with a fin glued on its back, and the ensuing "dinosaur" battle, allows them to make their getaway.
 * In "The Little People," an episode of The Twilight Zone, a spaceman discovers a race of ant-size people and uses his size to proclaim himself their god...until two spacemen who are giants even to him show up.
 * This occurs several times in Walking with Dinosaurs
 * The Borg were, for a long time, one of the most feared and dreaded races in the universe. However, the Borg's first encounter with Species 8472 (as the Borg called them) proved this Trope in spades, as their ship annihilated two Borg cubes effortlessly before they could even finish their well-known  "resistance is futile" routine.

Music

 * I know an old lady who swallowed a fly... and an increasing sequence of critters each swallowed to catch the previous one.

Tabletop RPG

 * Forgotten Realms have this as one of main unwritten laws. The only one who wasn't subjected to the Worf Effect is The Simbul, though even she was either fought to exhaustion or swamped in other problems.

Video Games

 * There are numerous places in the Half-Life series where - while Gordon Freeman doesn't exactly need the help - members of different factions fight and kill each other, effectively clearing Freeman's path (Marines and Xen aliens in Half-Life, Combine, Antlions and Headcrab Zombies in Half-Life 2 and its Episodes). Closer to the trope, this leads to at least two instances where a rampaging Antlion Guard slaughters a squad of Combine soldiers.
 * This trope is the major point in one of Pop Cap Games, Feeding Frenzy. Eat small fish, become large fish, and avoid the even larger fish while doing that. Most levels have non-edible fish (which means, they eat you), or something else capable of killing you (mines or birds, or both!) but in several level you get to be top dog of the seas.
 * No matter what fish you are in Odell Down Under, there is always something that can eat you. Even the largest fish, the great white shark, can still be eaten... by another great white shark.
 * In God of War: Chains of Olympus, Kratos fights a Cyclops, which is then eaten by a basilisk.
 * In Adventure Quest when you do the "Big Trouble in Little Granemor" quest you're attacked by a Giant Hungry Zombie after fighting off some vampires. The zombie makes about one attack before a Ribber randomly comes up and drags it away (with its mouth).
 * Spore features this trope quite prominently, particularly in the Cell Stage. If you happen to be in the middle of being attacked by a large organism, once in a while a larger creature comes along and scares off or eats your attacker.
 * In RuneScape's "Ritual of the Mahjarrat" quest, is killed by.
 * You barely avoid a beheading in the opener of The Elder Scrolls V: Skyrim, thanks to a dragon rampage.
 * It can happen in-game, too: dragons can randomly attack while the player is fighting off weaker enemies.
 * In Parasite Eve 2, ANMC's are running rampant throughout the Shelter, having killed  the humans inside and many in a nearby town. It's only after Aya   that the Golems show up. If you thought the ANMC's were bad, you are going to get a very rude surprise. The Golems eventually run into their own bigger fish....
 * Musashi: Samurai Legend had a literal example with the Crimson Gorger. After the fight, it's about to eat Musashi, it then gets eaten by the Great Crimson Gorger, who then proceeds to continue the chase and therefore the boss fight.

Web Original

 * In the Kate Modern episode "Answers", Michelle Clore orders her Shadow to carry off Lauren. As he is doing so, arrives and beats the Shadow in the face repeatedly with a golf club, apparently just for the hell of it. Lauren escapes.
 * In "Love on the 436", advances on the K-Team, only to get beaten up by the Shadow.

Web Comics
""Nothing beats Biggest Shirley.""
 * The Trope Namer was parodied in Darths and Droids, where the event convinces Qui Gon that he can cast Summon Bigger Fish. It becomes a running gag that Qui Gon thinks about casting it numerous times, never actually getting outright overruled due to circumstances steering the decision away from that.
 * Well, there was as alternate version...
 * In this Sluggy Freelance strip, the Godhounds attacking the house get taken out in one panel by the Mind Wedgier, a soul-eating Eldritch Abomination.
 * In a much earlier and more humorous example, Torg is about to be kissed by the ugliest woman in the world, but she is suddenly eaten by the alien that followed him from another dimension. She (the alien this time) seems about to eat him too, but he's still relieved.
 * Orbital beam weaponry in Adventurers!. Oh, yes.
 * In the webcomic Evon, the title character is about to be raped by Legune, the mad scientist holding her prisoner, when he's chased off by his patron, the mage, Maximus. But Maximus only stopped him to keep him from messing up his own plans of using Evon to breed a race of super mages. And he planned on starting right then and there... when HE is stopped by his Cabal superior, Ferneris, who is rather ticked off that Maximus disobeyed his orders to bring Evon to the Cabal. Violence ensues.
 * Inverted in this Cul De Sac strip.


 * Shmorky did it to Pac-Man.

Western Animation

 * In the fourth episode of Avatar: The Last Airbender, Aang stops at Kyoshi Island to ride the elephant koi, koi-like fish at least 15 metres long. Later, we meet the Unagi, the sea serpent that eats them.
 * In the first episode of the third season, a giant serpent attacks the ship of the group, and then goes after the enemy ship that was attacking them, after a Tempting Fate phrase by Sokka.
 * In several classic Warner Brothers & MGM cartoons, one throwaway gag would be for a fish to eat something, then a bigger fish would eat that fish, then a bigger fish would eat that fish, then a punch line to the bit.
 * Parodied in one episode of The Simpsons, where the 3-eyed fish is eaten by a 6-eyed fish, which is then eaten by a 9-eyed fish. Which is then eaten by a swimming Homer.
 * In the Family Guy episode "Lois Kills Stewie", Lois describes via flashback that she took a job at a fat camp. At one point she has to take one of the campers out of another camper's mouth ('cause he's fat see, so he'd want to eat whatever he could), and then she has to pull another camper out of the mouth of the camper she'd just rescued.
 * In the episode of The Grim Adventures of Billy and Mandy where the zombies attack, Billy is attacked by a rope of zombie sausages, which were then eaten by a zombie dog.
 * There's always the classic gag from Looney Tunes, in which Granny picks up the dog and hits it until it spits out Sylvester, only to then pick up Sylvester and hit him until he spits out Tweety.
 * Wild Kratts: This happens no fewer than two times in quick succession in an almost Xanatos-like way. A giant squid and a mama sperm whale are battling it out over the baby sperm whale, when a net comes out of nowhere and takes Mama out of the fight. So Big Daddy Sperm Whale shows up and promptly makes calamari of the squid. Enter colossal squid.
 * Played with in an episode of Angry Beavers where Norbert is admiring a rare fish in the river where their dam is. The fish is promptly eaten by a larger fish, which is eaten by another. This continues until the largest fish is eaten by a fish that was even smaller than the first one. Then that one is eaten by a orca whale.

Real Life

 * Invoking this trope is one of the most favourite attacks against "First Cause" arguments: Atheist, Agnostic or similar Skeptic: If God created us then who created God? And why does it have to be just God?
 * Subverted by Anselm's Ontological Argument, which is a logical attempt to prove the existence of God. Its main premise is that if God, i.e., an all-powerful being, did not exist at some point, then there would have to be a bigger "fish" to bring Him into existence, and then He would not be all-powerful, and therefore not God. According to Anselm, something which exists is 'greater' than something which doesn't exist. Since we can conceive of God existing and not existing, and the existing one is 'greater', then God must exist since he is the 'greatest' possible being we can conceive.
 * The food chain (or more accurately, the food web).
 * However, fictional depictions often do it wrong by having the bigger fish be not that much bigger than the one it takes out. In real life, a predator will rarely attack another predator that's close to its own size. Because even if it's successful, the odds of getting injured are high, and animals in the wild don't exactly have medics on hand to treat their injuries. Thus, hunting something that can put up a credible fight is high risk for low reward.
 * Pack predators may bring down larger prey with some frequency. In addition, there are rarely more than two or three levels of predation before reaching an apex predator. Each time a thing is eaten (a change in trophic level), there is usually a loss of at least 90% of the caloric energy from one level to another. In the simple chain grass - herbivorous insect - small bird - falcon, there were probably 1,000 calories worth of grass for every 1 calorie of falcon at the end. Food webs rarely have long, long chains of predation.
 * There is a Permian fossil of a shark that ate an amphibian that had eaten a fish.
 * In 2009 off the eastern seaboard of Australia, a three metre (ten feet) great white shark was found entangled in shark nets. The nets hadn't killed the shark, in fact, the shark had been bitten clean in half by something twice as large. Only in Australia, folks.
 * If you're wondering what could have done that: Another Great White, a Saltwater Crocodile, or an Orca.
 * Point of order: The shark was still alive when it was hauled out of the water. Great whites are amazingly tough to survive a wound like that.
 * Proponents of globalization and similar trends point to this as a way to ensure world peace. The bigger fish in this case is economics. If two or more countries are intimately tied together economically, then they can't attack each other because even the victor would be greatly damaged by the economic repercussions. This was one of the driving forces behind the founding of the European Union and is cited as a major (if not predominant) reason why war between China and the United States is almost impossible in the current economic climate—which is one reason China is working hard to find other markets for its products so it has more options in its foreign policy, especially when it comes to such hot topics as Taiwan.
 * Yes, because nations economically, integrated,with each other never go to war. There is no such thing as reputation, lust for conquest, or resentment.
 * War between Canada, the United States, and Mexico was once a likely scenario and became reality in the War of 1812 and the Mexican-American War of 1848. Nowadays, war between the three countries is almost unthinkable, mainly because large percentages of their imports and exports circulate among each other-in Canada and Mexico's cases, the overwhelming majority of exports go to the US. Only 21% of the US's exports go to Canada and Mexico, but that's still 5 times more than goes to China.
 * Not just imports and exports of finished products, either: in some businesses the manufacture of products depends on parts coming from the other country. The automobile industry is the best example, with an automobile assembly line in Michigan installing engines made in Ontario made from parts from Ohio (or the reverse).
 * In the Florida Everglades, alligators have been the apex predator of the swamps. But now, reticulated pythons introduced by humans have invaded the swamps and have been found eating the alligators.