How Did You Get Here?! (Unexpected Ways Species Travel the World)

by birtanpublished on August 4, 2020

in most cases the way species spread from place to place is relatively easy to understand like squirrel is born squirrel grows up squirrel decides they're sick of living in the same old tree where they've

Always lived so they wander to the next habitat over and before you know it the entire continent is covered with squirrels it's not always that simple though sometimes species end up in places we

Wouldn't necessarily expect to see them for instance groups of the same or very similar species can end up on opposite parts of the globe separated by hundreds of kilometers or

Entire oceans when two species that share a common ancestor have a lot of geographical distance between them that's called disjunct distribution and although it's puzzled us for decades

We're finally starting to understand some of the many reasons species show up in the most unlikely places first the obvious humans are long-distance travelers and habitual migrants

And we don't always think about what we might be dragging around with us so we're a major driver of disjunct distributions but this isn't new we've been doing this for thousands of years take the story of the eurasian

Pygmy shrew for example pygmy shrews live in a lot of european countries and regions from britain to iberia to italy and the balkans they also live in ireland which is a bit strange because ireland is an island and it's not where

Pygmy shrews evolved for a long time people just assumed that shrews got there thanks to some kind of temporary land bridge between ireland and britain but recent genetic evidence shows that the irish shrews actually have the same

Lineage as shrews that live in andorra more than a thousand kilometers to the south if there had been a land bridge you'd expect to see shrews descended from british populations as well

But the fact that they're descended from animals in andorra suggests that the shrews were probably brought to ireland on boats by humans not on purpose though see pygmy shrews don't generally burrow but

They might take shelter inside piles of hay where they can be relatively safe and also have easy access to the spiders and other arthropods they eat and when humans brought their livestock to ireland

They also brought hay for the animals so the pygmy shrews hiding inside it probably just hitched a ride this sounds like a story that could have happened last week but researchers think this happened a long time ago

Either when humans first came to ireland five to ten thousand years ago or after early trade routes were established so we've been spreading invasive species for thousands of years which is both fascinating and maybe a

Little sobering too like we mentioned earlier though plenty of disjunct distributions don't involve humans including some caused by range fragmentation this is when multiple

Groups live in the same basic area but with a sizeable gap between them and it explains the homes of the screaming hairy armadillo like other armadillos this species has armor but it also has a lot of hair

And it screams when threatened so there's the complete picture for you screaming hairy armadillos live in the arid and semi-arid regions in parts of argentina bolivia and paraguay but the range is split into two distinct

Sections with 500 kilometers between them that's range fragmentation at its finest one hypothesis about how this happened is that this species moved toward the atlantic coast back when the climate

There was dry see screaming hairy armadillos are adapted to living in dry places they love loose sandy soil and they can go a long time without water and during the pleistocene

Between 26 million and about 12 000 years ago glaciation kept the climate pretty dry and comfortable for them but at the end of that era when the glaciers began to retreat the

Climate turned humid as a result the intermediate population of armadillos became extinct while the smaller population continued to thrive on the armadillo-friendly shelly soils of the atlantic coast now

Beyond helping us solve mysteries range fragmentation can also teach us how vulnerable species are to changes in climate like if the climate changes faster than an animal can adapt we might see that reflected in how the

Animals are distributed and also sometimes when we look at that information in the context of geologic history like in this case we can even get clues about what the climate was like in the distant past

Next most people think of marsupials as an australian thing kangaroos wallabies koalas these animals all belong to a unique group of mammals that live on the continent of australia but you can also find marsupials across the

Ocean like the common north american opossum is a marsupial and dozens of opossum species also live in south america in fact scientists think that marsupials evolved

In north america then spread south so how did they end up in australia well during the late precambrian around 600 million years ago south america australia and antarctica were all part of a super continent

Called gondwana residents of gondwana could comfortably travel from one place to another without fins or wings which was handy if your goal was to spread your jeans

Across the globe so after marsupials arrived on the shores of antarctica back when it was green and had actual forests they went by foot to australia then australia and the other continents we know today

Eventually broke away and drifted to their current locations the marsupials range literally split up and over time the animals evolved into the species we're familiar with overall geographic forces

Work pretty slowly so for a long time it wasn't obvious how such similar animals could end up on opposite ends of the globe but as we've learned more about how continents drift and discovered related

Fossils around the world we've been able to piece it together sometimes species end up with weird distributions not because anything changed about earth but because of their own biology like

With mangrove trees mangrove trees may have evolved somewhere in the indo-west pacific or near the tethys sea an ancient body of water that stretched from present-day turkey to indochina but now

They exist on roughly 75 of the world's tropical coastlines range splitting and continental drift can explain some of that but the tree's affinity for long-distance travel also has something

To do with its seeds mangrove trees grow in habitats that are regularly flooded by seawater so they've had to develop unique ways to spread their seeds around many plants have evolved seeds that can drift on the

Wind or be carried by pollinators but mangrove seeds are buoyant this isn't unique to them and the reason why is simple if you're going to disperse in water you need to be able to float but as a very

Nice side effect the seeds that are good at being buoyant also tend to be good at traveling long distances so you could view this as a sort of accidental side effect of the adaptation that mangroves needed

To reproduce in a challenging habitat even though natural selection doesn't really favor broad distribution directly buoyancy allowed the plant to spread its genes to faraway places and thrive all over the world this next

Example is one of our favorites because not only has this animal ended up in distinct habitats because of its own biology it's relied on the biology of other species killa fish

Are colorful cute fish known for ending up in weird places including temporary ponds and isolated bodies of water and worldwide they can be found on every continent except australia and antarctica overall

These things are tough some species lay eggs that can survive long periods in completely dry conditions which explains how they end up in seasonal ponds but what's even more

Impressive is how at least some killer fish appear to have arrived in new habitats scientists have suspected that these fish may sometimes resort to shall we say unusual dispersal

Techniques the existence of remote populations in bodies of water at high altitudes for example were kind of hard to explain then in 2019 a group of researchers in brazil

Officially discovered that killifish can get around in the most unpleasant way i'll just say it they get pooped out because some killer fish eggs can survive being eaten when the researchers

Fed killa fish eggs to cascaroba swans they found that at least a few of them came out the other end relatively intact that's partly because of that thick membrane that helps

Protect the eggs from harsh conditions and partly because the birds have inefficient digestive systems so the eggs can travel long distances inside the creature that ate them and then get dropped into some random pond

Where they might actually hatch we've suspected for a long time that birds are responsible for dispersing seeds blackberries probably have the odd and scattered range they do because of birds but this was some of the first

Evidence that fish can also be dispersed this way and so far it looks like killer fish aren't the only ones in june 2020 another paper came out showing that the same thing can happen with mallard ducks and carp eggs so if you're wondering how

Fish got into your neighborhood pond that might explain it finally of all the examples we've talked about this one might be the cutest it involves iguanas which are found in two main areas

In the americas from florida to southern brazil and also in the caribbean it's pretty obvious that iguanas crossed the ocean at some point because there really aren't any other good explanations for their presence on so many isolated

Islands what's less clear is how they did it iguanas are good swimmers but they're not michael phelps or anything still they got to those islands somehow and one prevailing hypothesis is that

They rafted there you know by floating across the sea on something like a boat before you get too many pictures in your head of iguanas building dugout canoes with their sharp claws

The rafts were probably built by much more natural forces for instance in 1995 a bunch of iguanas arrived on the caribbean island of anguilla on a large mat of uprooted trees which could have been made during something

Like a hurricane that doesn't prove that's how all iguanas traveled around the world but it did demonstrate that this is possible and even beyond iguanas this form of distribution could explain a lot of things about how animals

Arrived on certain land masses the ancestors of lemurs for example probably got to madagascar in much the same way which sounds like a pixar short waiting to happen the general idea is that large mats of debris produced by

Hurricanes could easily transport several members of one species and eventually you'd end up with a whole viable population so the way animals spread across the globe isn't always as simple as squirrel a moves to point b

And so on and so forth animals also get distributed in amazing complicated ways and understanding how that happens can help us learn a lot about evolutionary history and to some degree those disjunct distributions can even

Help us understand how the world we live in has changed over millions of years thanks for watching this episode of scishow if you want to learn more about animals living in weird places

We've got another episode you might like it's about some animals who are living their absolute best lives in cities and you can watch it after this

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