Hi. It's Paul Andersen and this Life Science Disciplinary Core Idea 2A (LS2A).
It's on Interdependent Relationships in Ecosystems. So this is at the level of ecosystems so how
communities, how biotic and abiotic factors all work together to create life on our planet.
And so how do we get students to that level of understanding? Well we start at the lower
elementary grades by talking about animals and plants. And so what do animals like this
meerkat require to survive? Well they feed on insects. They feed on pretty much anything
that they can find. So they need food. They need water. They need shelter or a place to
live. And they're going to live underground. And then they need a suitable temperature.
So it's not too hot and it's not too cold. But they really rely on plants. Even though
they're eating a lot of animals, those animals are eating plants. And so animals are beholden
to plants for food. Also for shelter a lot of the time. And so what do plants need then?
Plants require air, water, minerals that they're taking in through their roots. And they also
require material from the air, like carbon dioxide. But the big thing that I'm missing
is that they require light. How are they different than animals? Make sure your students understand
that they can create their own food through photosynthesis. And animals have to either
eat plants or thing that eat plants. Now plants don't have it all their own way. They can't
move. And so they rely on animals to pollinate or to move their pollen around. And each of
these plants are evolved to their specific environment just like animals. And so a cactus
is going to have different water requirements obviously then a lily pad. But they all do
well where they live. As we move up in elementary we should start to talk about levels of feeding
and then food webs. And so the idea of the what a producer is pretty important. A producer
is going to be an organism that can produce their own food. And so plants are that. But
there are other things, like in the ocean, phytoplankton are really important producers
on our planet. So they're producing food and then that food is consumed. So consumers eat
producers. Or eat things that eat producers. So as we move up this would be a primary,
secondary and tertiary consumer. That means that they're eating things that eat plants
or eating plants themselves. Now those aren't the only two groups, producers and consumers,
because when we die we have to move the material back into the ecosystem again. And we do that
using decomposers. And so worms, or mushrooms and funguses are very important decomposers
and so are bacteria. And so we should really introduce the idea of a food web at this point.
A food web is going to show how matter and energy moves in an ecosystem. And so for example
this beetle is feeding on a tree, but it's eaten by a frog, which is eaten by a snake,
which is eaten by a coyote. And so it's important that they understand where the arrow is moving
and what it represents. It represents the movement of energy and matter. And so I shouldn't
even have to have the diagrams on it. You should be able to figure out what these two
question marks are really representing. Since this one right here has arrows moving out
from it, we know that it is a producer. And since this one only has arrows coming into
it, we know that it is a consumer. A tree and a coyote. Okay, now in a ecosystem we
want it to be healthy. And to be healthy you have to have as many of these different relationships
that you can. So big changes in one area aren't going to effect the whole of the ecosystem.
So this is a food, a simple food web, of Lake Michigan. You can see how complex it is, with
all the producers and then the consumers and the consumers that eat them all the way up.
Again it's healthy if we've got a lot of species in a food web. But we can have things introduced
into an area that can really decimate it. So the zebra mussel is an invasive species
that was introduced into Lake Michigan. It's eating a lot of this phytoplankton and so
it's going to disrupt that whole food web all the way up. As we move into middle school
we really want to talk about the specifics of ecology. And for me it's important you
understand what is an ecosystem? What is a community? And so I wrote this little BECPO.
It's the way that I remember the different levels within ecology. It stands for biosphere,
ecosystem, community, population and organism. So an organism is one individual. A population
would be all of those individuals in an area like all the beetles in an area. A community
is going to be all the populations that are interacting together. And then an ecosystem
is going to be all of the communities, but we also have to add one more thing to define
an ecosystem. Because all levels here within ecology have what are called biotic factors.
Biotic factors means living factors. But when we get to the level of an ecosystem then we
add abiotic factors. Things like light, water, availability to minerals, temperature. All
of those thing are abiotic. And so we don't introduce those until the level of an ecosystem.
So community is just going to be biotic factors. But once we get to an ecosystem, now we're
adding things like abiotic factors. And a biosphere, what is that? That's simply all
the ecosystems that we have on our planet. So it's important you know the different levels
of organization within ecology. And then some of these terms and how those populations interact.
So competition is going to be individuals who share resources. And so for example these
red deer are fighting, or they're competing in this case, they're competing to mate with
the females. But these anemones are fighting. They're actually fighting for control of this
bottom part of the ocean. They're sharing those resources. Predation is different than
that. Predation is when you have a predator and a prey and the prey is eaten by the predator.
So for example this tiger feeding or these ants feeding on this katydid is going to be
an example of predation. Mutualism is where they both benefit. And so an example that
you're probably family with is the clownfish and the sea anemone. Where the clownfish is
immune to the toxins on the anemone and keeps things away from it and can clean up food.
And also brings food towards the anemone. Or pollination. So this humming bird is getting
nectar from the flower. So it's benefitting. But in return it's pollinating that flower.
So these are all interactions now at the level of a community. And so populations tend to
increase over time. And so when we now get to the level of high school we should be talking
about population growth. Exponential growth. And so basically any population, it doesn't
matter what it is, elephants for example. If they all reproduce and they all survive,
they're going to show what's called exponential growth. Even though it takes a long time for
them to reproduce. I mean just think of humans. It takes quite awhile, decades, for us to
reproduce, but we're seeing exponential growth right now. And so if you have the requirements
for life, if you have the abiotic and biotic factors required for life, then populations
will always undergo exponential growth. What that means is that they're going to increase
very, very dramatically and very quickly. But over time you're eventually going to deplete
those biotic and abiotic factors. You're going to run out of resources and so you're eventually
going to hit something called a carrying capacity. Carrying capacity is the maximum amount of
organisms that an area can support. And so it doesn't look like this. It's not all smooth.
This is just a mathematical representation. Let me give you an example of what this looks
like. And so the wolves were introduced into Yellowstone Park in the early 90s. And this
is the data since the early 90s until today. And basically this blue bar is going to show
all the wolves in Yellowstone Park and then you have the numbers over here on the side.
And so what happened to the numbers in Yellowstone Park? Well they went through exponential growth.
They got really a number of wolves in the park grew dramatically. And then what happened
is they started to deplete their resources. They ate too many elk. They ate too many bison.
They ate too many dear. And eventually the population drops down and it comes up and
it comes down. And so we get this nice oscillation where the predators start to drop off, now
the prey can come back. But really what we have is now a carrying capacity. In other
words this is going to be the maximum number of wolves that Yellowstone Park can support.
And so now we're at the level of an ecosystem. So we're at the level of organisms interacting
with both the biotic and abiotic factors. And I hope that's helpful.