Hi. It's Mr. Andersen and welcome to biology essentials video 50. This is on
populations and how populations interact with one another. One of the most famous words
in all of biology is called symbiosis. Symbiosis basically means living together. Or same life.
And so an example of this would be the clown fish and the sea anemone. Clown fish lives
in the sea anemone. Sea anemone gives them protection. They have these stinging cnidocytes
in their tentacles. And the clown fish is immune to those so they can live within the
anemones. So they get protection. What do they give the anemone? Well they're going
to feed on little invertebrates that normally might damage the anemone. That would be one
thing. And then they're going to secrete ammonia. And that ammonia is going to be used as nitrogen
inside the algae that live in the anemone which is another symbiotic relationship. And
so that's basically what I'm going to talk about. Relationships between populations.
And so these interactions can have effects. Sometimes those effects are good. And they're
positive. Sometimes they're negative. And sometimes they're neutral. And so if we look
at all these interactions between populations, those that are positive, those that are neutral,
those that are negative, we have all these different types of symbiosis. Some that are
good. Some that are bad. And some that are neither. And so basically we'll go over all
the different types. Remember though that in an ecosystem the symbioses can help an
ecosystem or damage it. And ecosystems are fairly stable but they're stable because there's
constant feedback mechanisms that keep those populations in check. Sometimes those populations
aren't in check. And a lot of the time that has to with changes in their environment.
It could be geologic changes. But sometimes it's just going to be human changes. Example
I'll talk about is the introduction of Kudzu which is a plant into the United States and
what that did. And so basically we could summarize all interactions between organisms on a matrix
that looks just like this. So this is going to be population X and population Y. And these
are all the different types of interactions that we could have. And so basically I'll
go down the list and we'll look at all of those interactions. Know this, that this is
just interactions between two types of populations. And ecosystems you could imagine are much
more intense than that. But let's start with the matrix right here. So first of all, we've
got wolves and lichen. So let's say in an ecosystem, the Yellowstone ecosystem, the
0 on this chart means it's a neutral to an individual. The plus means it's good and the
minus means that it's negative. And so I tried to come up with a neutral interaction between
the two. And so one where neither are effected by the other. And so this is a type of lichen
that grows on a rock. This is a wolf. And wolves don't feed on lichen. And lichen don't
require wolves to live. And so we would call this neutralism. In other words neither of
them benefit from this reaction. Now, I would almost argue that there's no such thing as
neutralism because maybe lichen get their nitrogen from birds that land on the rock
and release some kind of uric acid. And they can grow with that. And if there's an increase
in the wolf population, it could lead to a decrease in this. You can see how this ecosystems
are so connected. The neutralism is probably just and idea, less than actually occurring.
Next one is called amensalism. Amensalism occurs when you have one organism that is
not effected by the other. Another organism that is negatively effected. So this is penicillium.
Penicillium is a type of fungus. It's constantly producing a toxin. And that toxin kills bacteria.
So in this case, the bacteria is negatively impacted. The penicillin doesn't even know
that it's there. And so we would call this a neutral effect. And so we call this amensalism.
Amensalism is when one organism doesn't gain anything from this reaction, but the other
one is negatively effected. Next on we go to, commensalism. Commensalism is when one
is positively influenced. And so I didn't know this. I learned about this, but the golden
jackal, golden jackal lots of times the males if they get driven out or individuals as they
get driven out, they'll just follow tigers around at a safe distance. And so they'll
wait for that tiger to kill something. And so they can get some scraps from it. And so
in this case they jackal is not going to effect the tiger. So that would be a neutral reaction.
But the jackal just by living around the tiger is getting a positive. And so we would call
this a commensalistic relationship. Where the tiger gets nothing, but the jackal is
going to get something good from it. Next we'll go to competition. So an example of
this could be the lion and the cheetah. They both feed on similar prey. And so if the lion
kills more prey, that's going to be less for the cheetah. And if the cheetah kills more
prey, that's going to impact the lion. And so we call this competition. And so lots of
times if a lion moves into an area and they can find cheetah cubs or cheetahs, they'll
kill them because they're in direct competition for the same kind of a food source. Next on
we go to mutualism. Mutualism remember is going to be when both benefit. And so pollination
is an example of mutualistic relationship between insects and flowers. And so what do
the flowers get? Well as an insect lands on a flower and starts to eat the nectar, so
it's getting food from the flower and they're attracted to that, it's also going to dust
that with pollen. And so as this bee moves away, it's going to move it to a different
plant. And so what's the plant getting? It's getting dispersion of its pollen or its sperm
to another plant. What's the bee getting? It's getting a constant food supply. And so
this is a mutualistic relationship. They both benefit. And if we look through time evolutionarily
we have this growth of insects along with a growth of plants. And then finally we have
plus minus. In other words we have either predation or parasitism. And so right here
we've got a preying mantis that is eating a bumble bee. So that's definitely bad for
the bee, but it's definitely good from the preying mantis. And so we would call this
predation. Predation is going to be positive for one, negative for the other. But parasitism
is the same thing. And so this would be a cowbird egg. An cowbird is a bird that will
lay its bird in other bird's nests. The cowbird will usually hatch first. It will usually
gain weight quicker. So the parent bird can't tell the difference between them. It will
keep feeding the cowbird. Cowbird gets bigger and bigger and bigger and bigger. It will
eventually push the other chicks out of the nest. And so that's a type of parasitism.
It's good for the cowbird. It's definitely bad for the eggs that are laying right there.
And so we call that a plus minus reaction. So those are all the different types. And
you should kind of learn these different terms. And examples of each of those. Now ecosystems
contain all these interactions between populations. But ecosystems tend to stay the same. And
they use feedback mechanisms to do that. So remember when we learned about feedback mechanisms.
This is an example of one. If you're driving down the road and you see this sign, you're
going to fast. So you're going to slow down a little bit. And then you're going to slow
down too much. And then you're going to speed up. And eventually you hit this checkpoint.
This would be a negative feedback loop that you're experiencing. But ecosystems are going
to see the same thing. And so wolves were introduced in Yellowstone Park in 1995. They're
population took off. Let's find a different color. Took off. And pretty soon there were
over 100 wolves, this is in the northern part of Yellowstone National Park. So what were
they feeding on? They were feeding on elk. So if we look at the elk population, elk population
was around 16,000. What happened to the elk population? Elk populations started to drop
off. So now there's not food to eat, and so the wolves are starving. So what's going to
happen to them? Their population is going to drop off. They're maybe going to have less
pups in their liters. Their population will drop off. What will happen to the elk population?
Well if there's less wolves, then they can have better calves. They're more likely to
survive and so they're going to increase. And so we're going to get this, let's get
a color that's right, we're going to get this fluctuating between the wolves and the elk
populations maintaining this kind of static equilibrium or this carrying capacity within
it. So it's kind of like a negative feedback loop. Where the number of elk dictate the
number of wolves and the number of wolves dictate the number of elk. So it's a feedback
loop. And it keeps them kind of at a constant level. Now what's interesting, when we talk
about populations is I'm talking about a population as a whole. Populations are made of a bunch
of individuals. And so this is a cool picture of these birds starting to migrate. And maybe
you've seen videos of this. But in any population, a population is made up of a bunch of different
individuals. Be it in a forest or in this herd. Or in here, which is a biofilm which
is set up between bacteria. And so all those choices made by individuals create a population
that has a specific behavior as well. And so each of the birds in this flock are just
trying to stay next to the bird next to them. A safe distance between the two. But we get
this living kind of a population. This living system that's constantly influx. But sometimes
populations get out of flux. Sometimes that feedback just doesn't work. And usually that
happens when we bring them from somewhere else. And so in 1876, in the centennial expedition
in Philadelphia, somebody brought this beautiful plant from Japan called Kudzu. And so Kudzu
was released to the United State in 1876. It's taken off and it's gone crazy since that.
And so much of the southeast is covered in this vine like plant. It was even used in
World War II. They released the humans, the American forces brought it to islands of like
Vanuatu, just so it would cover up their material. Just kind of to disguise plants living on
that area as a camouflage. But once you introduce it into a new ecosystem there's nothing that's
evolved to feed on the Kudzu. And as a result, Kudzu took off. And so it's population grew.
And there was nothing that was stopping it. Until now. Now we have this bug that has made
it's way here as well. So we would call Kudzu an invasive species. But now we have this
bug. It's made it to the United States. And it is evolved to feed on Kudzu. And so here's
Dr. Jeremy Greene. I think he works at Clemson, but basically what they're doing is looking
at the growth of this bug. "It has since covered South Carolina entirely. It has covered most
of North Carolina. And now most of Georgia." So this is a Kudzu stink bug. And we're seeing
huge growth of this as it feeds on the Kudzu, which didn't have a predator before. And so
it will eventually maintain some kind of a symbiotic relationship between the two. And
some kind of a homeostasis. But when humans make big changes, ecosystems are, it takes
awhile for them to actually respond. But with humans moving around this planet, it's going
to be a hard thing for that to stop. And so that's populations. Those are interactions.
And I hope that's helpful.