Hi. It's Mr. Andersen and welcome to biology essentials video number 7. Double
O 7. This video is on speciation and extinction. And so it's really on just two things. In
other words it's how we go from one species to two and then how we go from one species
to no species. And so this is right here is a tapulasaurus. It's a saurapod that was found
in Brazil and you can see it right here in this phylogenetic tree. And so if we trace
the phylogeny of a tapulasaurus, what we would find is each of these points here represents
a common ancestor of the dinosaurs above it. But because it branches in either direction
that means we're going from one species into two species. And that's called speciation.
And we will talk a little bit more about the mechanisms by which we can speciate. But essentially
in speciation you go from one species to two. Extinction is when you go from one species
to zero species. And so where do we find that on here? Well, on the side you can see we
have time, so we have time on the side, so this is millions of years ago. And so you
see that some of these'll end. In other words Nigersaurus, right here, ends and that means
that it went extinct. In other words this one species became zero species. And so, in
life we go from that first common ancestor of all life but we've gotten a diversity of
life through speciation. But remember also along with that we have a lot of extinctions.
In other words the survivors are surviving on the backs of those that don't survive.
And so this video is really only about two things, but it will be in a little more detail
than that. And so, how do we get new species? That's through a process called evolution.
It's biological evolution or change within a gene pool. So there are two things kind
of in play with speciation and extinction. In other words when one species becomes two
that species is evolving or changing or separating into two populations that are reproductively
isolated. And so evolution can give us diversity. But as that environment changes it can force
speciation and that environment can also force extinction. And so there's this play between
evolution, environment, and then speciation and extinction. This remember creates more
diversity and and this actually creates less. So taken to these extremes, one specific type
of speciation where you see incredible rapid rate of speciation is called adaptive radiation.
That usually happens when we open an new niche. And likewise, when you have a bunch of extinctions
at one time we call that mass extinctions. We've only had about five of those through
the history of life on our planet. So let's start with speciation and let me give you
a real example of that. This is the three-spined stickleback. Three-spined stickleback and
the study I am looking at here was in Loberg Lake which to kind of orient yourself, here's
Anchorage right here, so we're in Alaska. Loberg Lake is right down the road from Wasilla.
And so speciation occurred in the stickleback or is occurring right now in the stickleback.
The three-spined stickleback has three spines that go out the back, but there are actually
two different phenotypes or two different varieties of stickleback. This would be a
low armored stickleback and it's found usually in a fresh water environment. But if we were
to look at the stickleback, the marine stickleback that spends half of its life in the ocean
and then comes back to actually breed, it'll have more armor on it, so it'll actually have
larger spikes. It'll have additional spikes down here. And then they have plates on the
side. So there are plates on the side of the stickleback that go all the way back here.
And so this would be what we call a fully-armored stickleback. And then if I get rid of the
coloring that would be a low armored stickleback. Okay. So a natural experiment was done in
1982. So in 1982 in Loberg Lake, we'll say Loberg Lake looks like this, almost all the
sticklebacks in Loberg Lake were of the low-armored variety. In other words they were just this
fresh water. And so what happened in 1982 is that they poisoned the lake. The sticklebacks
don't really have a purpose, they do but they wanted to put trout and salmon back into the
lake. They wanted them to grow. And so they poisoned everything in the lake. So they killed
all the sticklebacks. So there were no sticklebacks in the lake so it's a great kind of experiment.
What they found is that over the next few years, fully-armored sticklebacks were making
their way into the lake. And so they were making their way probably through streams,
and out from the ocean and making their way back into the lake. And so what we had in here
was fully-armored sticklebacks. And over the next few years their population started to
grow. Eventually they started to notice hey there are fully armored sticklebacks in here.
And so what they found then over the next few years is puzzling. In other words the
fully-armored sticklebacks started to drop off. Their numbers started to drop off and
then they started to see an increase in the low-armored stickleback. In other words their
population started to increase to the point where if you go to Loberg Lake right now you
are going to find almost all of the low-armored sticklebacks and not many of the fully-armored.
And so this is kind of a cool experiment where you can actually see speciation taking place.
Now why would you see that? If you think about it, for me, I would think, man more armor
the better. Why wouldn't I want as much armor as I can. But the predator that they're facing
was one of the most scary predators in all of science if you were small. So this right
here is a dragon fly larva. Dragon flies, remember, are very beautiful but they spend
a lot of their life under water. And they form as a nymph or a dragon fly nymph or larva.
And so this is one hunting. This is a video from David Adenboro. And so let's watch it
feed. Wow, ok that's a little bit disturbing. And so the dragon fly larva is the major predator
in Loberg Lake. And so the low-armored sticklebacks actually grow faster than the fully-armored
sticklebacks. And so the fully-armored sticklebacks were being preyed upon at a greater rate by
the dragon fly larva than the low-armored sticklebacks. And so we had natural selection
taking place. And so what we're starting to see is a change in that. Now eventually if
fully-armored and low-armored sticklebacks can't interbreed then we have those as a separate
species. And so on that tree of life, we can go from one branch to two. Now, again, taken
to its extreme, we can have what's called adaptive radiation. And so once you have a
new environment where species can take off and there's no predators, you get a huge amount
of diversity. And so when we talk about evolution we have a tendency to fixate on the Galapagos
Islands and neglect the Hawaiian Islands. And so this is a great picture right here
of the Hawaiian Islands. But what we found is that it was hard for a lot of species to
get to the islands. Mammals weren't going to make it but birds could make it easily.
And so the honeycreeper is an example of a bird that just went crazy on the Hawaiian
Islands. And so we think the ancestor of modern day honeycreepers was a bird that looked this.
It was somewhat similar to a finch, but once it arrived on the island it was a founding
population. You got this huge diversity of all of these honeycreepers, you can see their
beaks are, each of them adapted probably to a different flower, and so we had adaptive radiation.
So we had this new niche show up, this new environment and they exploited, excuse me,
this new environment show up and they all exploited all these different niches. And
so you have this great diversity of honeycreepers. Now a lot of these are pictures and not actual
photographs. And the reason why is that humans showed up and with humans, then we had predators
that showed up and they started to make a lot of those species go away. And so extinction
started to show up as well. What's another famous adaptive radiation? Well I could think
of a couple. One would be the arrival of mammals. And so once the dinosaurs went extinct and
mammals were able to grab a foothold, they adaptively radiated to fill a bunch of different
niches that were once filled by dinosaurs. Or adaptive radiation, we can also see in
the Galapagos, as they move from island to island like the beak of a finch which is just
one population on the Galapagos. Now the flip side of this podcast is the idea of extinction.
And I love this quote right here, it's the idea that 99.9% of all species that have ever
existed are now extinct. And so these are some species, the Auroch, the Quagga, the
Great Auk, the Thylacine or tasmanian wolf, these are all species that have gone extinct
just in the last few hundred years. And they did that as a result, a lot of these as a
result of human pressure. This would be a Golden Toad that went extinct in the 1980s.
And so if we look on this tree of life, each of these branch points here would be an area
of speciation. But each of these end points would be an area of extinction. In other words
that once you have that last organism die of that species, then you can't pass that
on, those genes on anymore and so we would say it's extinct. Now the things that are
alive today are called extant. But if we look through the history of life we find some times
there are massive extinctions, extinctions that go across all. Alright, scientists have
identified five different mass extinctions over time and they're labelled here with these
yellow triangles. This would be the \cf2 \cb3 ordovician silurian\cf0 \cb1 extinction, this
would be the late devonian, this is the permian triassic extinction, this would be the triassic
jurassic extinction and then this right here would be the cretaceous tertiary extinction.
And so what makes a mass extinction? It's an extinction where the rate of extinction
is just dramatic. And so we also have other extinction events here within this. This one,
a couple of interesting ones that you maybe know about. This right here would be the permian
triassic extinction. This one is known as the Great Dying. And so of all of the extinctions
this is the biggest one. During the Great Dying, something like 70% of all land species
and 96% of all marine species went extinct. And there are a number of different causes
of that probably. The one extinction that almost everybody is familiar with is the K-T or cretaceous
tertiary extinction. And so that's the one where the dinosaurs actually went away. And
so with all of these extinctions, scientists are trying to piece together what actually
causes it. And so a lot of these are suspects. In other words the Great Dying formed at the
same time when Pangaea actually formed. And so scientists think that that had something
to do with it. But it could have also been volcanoes. It could have also been oceans
losing their oxygen. And so these are all the different types of characteristics that
could have led to mass extinction. And so scientists are kind of piecing those together
and figuring out which one of those caused each of these different extinctions. The one
that I want to talk more about specifically is the K-T extinction or the cretaceous tertiary
extinction. And the evidence there is pretty good. This is where dinosaurs go away. It's
probably not super accurate to say that. There's a lineage of dinosaurs that continues today
and those are called birds. And so birds, it's a lineage of dinosaurs that continue
today. But most of the dinosaurs actually disappear at that time. And so the point in
the fossil record where they disappear is sometimes referred to as the cretaceous or the
K-T boundary. And if we look below that we find dinosaurs and if we look above that we
find no dinosaurs in the fossil record. Now you've probably learned that there was a giant
asteroid that hit around that time and we think that it hit in the Gulf of Mexico. We've
actually isolated where that crater is. But what evidence would we have to show that this
actually exists? Why isn't is something else, like climate change for example? Well one
piece of evidence is that down here we have dinosaurs. Above here we have no dinosaurs,
but we also have a level of iridium that goes around the planet. So a thin layer of iridium
that's found along the K-T boundary. Iridium is really rare on our planet, it is not very
common, but in asteroids it is incredibly common. And so that's one piece of evidence
that suggests that this asteroid impact could have led to the disappearance of the dinosaurs.
And so that is an extinction. And so again to summarize we've got speciation where we
make new species and extinctions where we get rid of those. And they're big at sometimes
and their rates are really high at sometimes and really low at other times. And mostly
that has to do with changes in the environment. And so I hope that's helpful.