Hi. It's Mr. Andersen. And in this podcast I'm going to talk about r and
K selection. Or r selected and K selected species. Right here we've got a chameleon
female that's just laid two eggs. Right here we have a frog that's just laid thousands
of eggs. One of these is an r selected. One is a K selected. If you know exactly which
is which right now then you probably don't need to watch the rest of the video. But for
those of you that are now left, let me talk about r and K selection. Basically we have
to talk about population growth. And so any population where you have a positive r. And
r stands for growth rate. If you ever have a positive r, you're going to follow a curve
that looks kind of like this. You'll first of all have exponential growth. And then eventually
you'll run out of space or food. There's going to be competition. And eventually you're going
to hit what's called logistic growth. And so we call this the j shaped curve. The exponential.
Of the sigmoidal or S shaped curve which is logistic. And so what is N? N is going to
be the number of individuals in the population. And so right here, if we put N on this side
and we put time on the X axis. As time goes on, the numbers are going to increase. So
this would be a low N value right here. And this would be a higher N value. And this would
be a really high N value. And so it's important that you know what N is. That's the number
in the population. r is the growth rate. Remember if it's ever positive, and how do we calculate
growth rate? It's basically the number of people being born minus the number of people
who die. If we ever have a positive one, then we're going to get this curve. Now it's not
always radical like this. Sometimes it's going to be really gradual like this. Sometimes
it's going to be incredibly quick. Depending on what the r value is. And then the last
thing is K. K stands for carrying, let's try to spell that right, capacity. And so basically
that means in an area for a certain population, there's like a maximum amount that they can
support. And so we call that the carrying capacity. And that's where the limit is. It's
eventually going to level out on that. And so if I were to talk about, in the real world,
because this is just a math formula. Basically in the real world we put wolves back in Yellowstone
Park. And so there was tons of food there. Not a lot of competition. And so basically
their growth rate went up. And then it's dropped. And then it's gone up. And it's dropped. And
it's kind of reached this carrying capacity, a maximum number of wolves that you can have
in Yellowstone Park. And so it's not as smooth as that. But it certainly has an r value.
The N value has increased and then it's reached kind of a K. So it's important that you know
what N r and K are. Another thing that's important is that you understand the way life exists.
This is the story of life and death. It's going to vary. And we really have three different
types. So you happen to be a type 1 survivorship curve. And what that means is think about
all of the kids in your class or all the kids who were born on the same day that you were.
Basically most of you are going to survive that first day. And most of you are going
to survive. Now a few people will die right away, but most of you are going to survive.
You're going to make it through your teenage years. And your middle ages. And eventually
you're going to drop off. And all of you are going to die in these last 10, 15, 20 years.
That's because we're type 1. We're humans. And we give a lot of, you can see this right
here, parental care to our offspring. Now if we look at a frog. Here's some frog eggs
down here. They show what's called a type 3 survivorship curve. On day one, thousands
of little frogs, almost all of them die. But a few of them survive. And then they're going
to level off. And then they're eventually all going to die. Now we also have something
in the middle. Type 2 we call that. Song birds are an example of that. And so they're going
to die off at a linear rate throughout their whole life cycle. And so robins are an example
of that. Robins on average live about a year. But some live a few months and some live three
years. But on average they're just going to drop off until they're all dead. The ones,
the cohort, the ones that are born on that one specific day. Remember, our environments
are going to differ. Sometimes we're going to live in environments that are relatively
stable, like a desert. And sometimes not so much. Like a rain forest or even a coral reef.
Especially right now. They're changing radically. Almost everyday. And so basically let's get
to what an r selected species is. r selected are going to be those that base their life
on r. And remember r is growth rate. And so these are species that want to quickly grow
and exploit a niche as fast as they can. And so these are things that normally live in
an unstable environment. They have high fecundity. What does that mean? Fecundity basically means
that they can make a lot of babies really really quickly. In general these things are
small. They don't live that long. And their offspring just kind of are spread to the ends
of the earth. And so an example of this would be a dandelion. They show up really early
in the spring. They reproduce quickly. If you've ever seen a dandelion when it goes
to seed, those seeds are just spread out. Given very little parental care. Bacteria,
insects, diatoms, which are algae are a type of this. Squid babies are essentially laid
by the females. Males put sperm all over that. You have these packets and then the parents
just head away. They just leave. And then eventually all of the squid are born. Most
of them are food for fish, but some of them are able to survive. And so that's the r selected
species. You're putting your life in growth rate. So what's K selected species? Well these
things are going to put their lives basically around carrying capacity. They're in it for
the long haul. They're in it for exponential and then that logistic growth. They want to
live a long time. Generally they live in a more stable environment. They're larger as
far as body size. They're going to live a lot longer. There's a lot of parental care.
So you as a human are going to be a K selected species. If we look at plants. Compare this
to the dandelion. A tree like this. Some trees will live hundreds if not thousands of years.
Whales are an example of K selected species. But you don't necessarily have to be big.
This is an arctic tern that lives decades. And they have a lot of parental care. And
so they're K selected species. Know this. That in life it's not always one or the other.
There are some species that actually show a continuum. And so a sea turtle, you might
look at a sea turtle. It's big. It lives a really long time. You might say maybe that's
a K selected species. But then if you remember how they're born, they're just going to lay
a bunch of eggs. Cover them up in a hole. And then just kind of swim away. And all of
these eggs are going to hatch. These little baby sea turtles are kind of on their own.
And so that would be more of an r selected. And so even within a lifetime you can be r
and K selected. And even by gender. So if you think about it, not humans per se, but
in animals, males tend to live more of an r selected species. Produce as many as they
can. Spread as much of their sperm as far as they can. Whereas females are more K selected.
Investing a lot in those offspring in that long haul. So let's go back and look at that
first slide. The chameleon, is it r or K selected? Well, it's investing is just these two eggs.
And so it's in it for the long haul. Where this would be an r selected species. And I
hope that's helpful.