Lesson video

Hello, everybody.

Welcome to your final lesson on ecosystems with me, Miss Roberts, I am so happy to be back here for your final lesson.

I've really enjoyed teaching you this unit and I hope you've enjoyed learning about it.

Today's lesson is all about what can cause disruptions to food webs.

So let's find out.

I've got Lenny the lion here with me and he is going to help me for our final lesson.

If you need to get and get the resources that you need you're going to need a pencil or pen a ruler and a notebook.

And if you want to your favourite teddy, pause the video and go and get the things you need now.

Okay, let's get started.

So my turn, your turn.

Star words, star words, star words.

Good job.

That first word is energy transfer.

You're turn.

The next word is producer.

You're turn.

The next word is primary consumer.

You're turn.

You're an expert.

All of these now team, well done.

The next one is food web.

Your turn.

Good job.

The next word is consumer.

Your turn.

Well done.

And the last coward is tertiary consumer.

Your turn.

What does tertiary mean again team? Third, well done.

So it's the third consumer in the food chain.

Okay, so let's get started.

In this food chain, I wonder what would happen if there was no producer, maybe there'll be no rainfall and the tree died.

So what do you think would happen? If we got rid of the leaf so that the caterpillar couldn't eat it, there'll be no caterpillars for the voles to eat.

And if there was no voles to eat, then the owl would die.

So what would happen? This knock on effect would mean that all the organisms in this food chain would die.

The only reason they might not, is if they could move to another habitat.

For instance if an owl didn't have any voles to eat where it was living it might be able to fly somewhere else, set up a new habitat and live there where there's food to eat.

So with this in mind, let's just do a quick recap of what a food web is.

A food web is where you have a series of interlocking food chains.

For instance, in this food web we had the grass that transferred energy to the deer.

It also transferred energy to the vole and the vole transferred energy to the fox and the hawk.

Can you tell your screen which organisms did the fox transfer energy to? What were those two on the right? Well done the wolf and the hawk, good job.

So this food web is represented, if all of these organisms are healthy and living, however, sometimes there are disruptions to a food web.

Disruptions means change.

So there may be a case where there is no grass the grass is either killed or something happens so that it is not there anymore.

We'll look at those reasons in a moment, so don't worry.

If there was no grass in this food chain all of the organisms would die because the grass is the producer, and without to producer, you can't have a food web, because if there was no producer, there'll be no deer.

If there's no deer, there'll be no wolf.

If there was also no grass, there'll be no vole.

And so the fox and the hawk would not be able to eat in which case all of the food is decreased, so all of the organisms would decrease and they would all eventually die.

Hi, my name's Miss Simpkin.

I'm sorry to interrupt your lesson on food webs.

But Miss Roberts has asked me to pop in because I'm a marine biologist, somebody who studies animals who live under the sea.

And she's asked me to give you another example of a food web, a marine food web.

I am currently studying different marine animals in Madagascar.

I'm putting my scuba kit on every day and I'm diving down to the coral reefs and I'm counting all of the different species that I see.

And something that I've noticed is that the number of octopuses on our coral reef, the number of octopuses in our coral reef food web is decreasing.

And I wonder if today you can help me think of some different reasons why that might be happening.

What the disruptions to my food web might be, that are causing my number of octopuses to decrease.

So, here's my research centre behind me.

You are going to help me be research scientists today.

And I am going to explain to you the food web that we are going to look at in this example.

So Ms. Roberts has already given you an example of a food web.

Here is another one.

So we're starting with our octopus and our octopus eats crabs and lobsters and our lobsters and our crabs in my marine food web eat a type of animal called a sea urchin.

My turn, sea urchin.

Sea urchins have spiky spines on them.

So look a little bit like underwater hedgehogs and our sea urchins eat sea grass.

Sea grass is the producer of our food web.

It makes its own food and provides the energy for all of the other organisms up the food web.

So, I've told you what eats what, I wonder if you control your own food web now because it's going to be helpful to have it in front of you for the rest of the example.

So if it was me, I would draw a picture.

I've put them in the right place for you as a hint of each of these marine organisms, or you could just write sea grass, sea urchin, crab, lobster and octopus, if you prefer.

And then can you draw the arrows to connect your food web? Remember the arrow goes in the direction of what is eaten by what? So if the sea grass is eaten by the sea urchin, then the arrow will go from sea grass to see urchin.

Can you pause the video and have a go at drawing your food web for this, for these organisms now.

Great, I'm going to show you a correct version.

Don't worry if you made some mistakes but can you check your answer? So you should have an arrow going from sea grass to sea urchin an arrow going from sea urchin to crab and lobster because the sea urchin is eaten by both the crab and the lobster, and then add two arrows one going from crab to the octopus and one going from a lobster to the octopus, because they're both eaten by the octopus.

If you need to edit your food web can you pause the video and do that now? Okay, brilliant.

So this is the food web that I've been studying.

And as Miss Roberts explained sometimes animals can be removed from the food web for different reasons.

And she's going to tell you more about those different reasons later.

But that can have an effect on other animals in our food web.

And so that's what I think is happening to my octopuses.

They're decreasing in numbers.

I've noticed on my dives, I'm seeing fewer and fewer octopuses.

And so I think it might be because of disruption somewhere in the food web, we're going to look at some different examples and make some predictions of why that could be happening.

So the first thing we're going to think about is what do you think might happen if we remove the sea grass from this food web? Can you make a prediction for me? Remember, our sea grass is our producer.

Remember Miss Roberts example of what happened when she removed the producer in the last food web.

Can you write down this prediction using this sentence? If sea grass was removed from the food web, I predict that, because, pause the video and do that for me now, please.

Great, let's see if your prediction is similar to mine.

So if we remove sea grass from the food web, then the numbers of all of the other organisms in our food web will decrease as well.

That means there'll be less of them, that's why we've got a down arrow.

And this is because the sea grass is the producer.

Give yourself a tick, if you wrote an answer similar to that.

Great, so that could be one reason why the number of octopuses in my coral reefs out here are decreasing.

That's one scenario that makes sense, maybe there's a reason why the sea grass has been removed and that's causing my octopus numbers to decrease.

Hmm.

On my dives, when I'm underwater counting my different organisms what evidence would I have then that this scenario might be taking place? That's right, I'd see less sea grass and I'd record less sea grass.

So maybe that's something I need to look out for in my research over the coming month.

Okay, let's look at a different scenario now.

Can you have a think, what would happen if the sea urchins were removed from my food web? So you've got your food web in front of you, so use that to help you imagine that the options aren't there what's going to increase and what's going to decrease.

You can use this sentence stem to write your prediction.

If sea urchins were removed from the food web I predict that the amount of sea grass would mm, but the numbers of mm mm and mm would mm.

Pause the video and write your prediction now.

Brilliant.

Let's go through this scenario.

So if we remove the sea urchins, then the numbers of crabs and lobsters are going to decrease because they have less food to eat.

And that means that the number of octopuses will decrease because they will have less crabs and lobsters to eat.

But, the number of sea grass, well the amount of sea grass will actually increase because there's less sea urchins eating it.

So that's another scenario that could be causing my octopuses to decrease.

What evidence would I need to look for on my dives to see if maybe this scenario was the case.

What do you think? Say it to your screen.

I'd have to count the number of sea urchins, and if I couldn't see many sea urchins, then that could be evidence, but also need to see that the amount of sea grass was increasing.

So if on my dives, I see more and more sea grass then this could be what's happening.

This might be why my octopuses are decreasing.

Wow, this is really helpful.

So you can mark your answer that you've written with your green pen.

The missing words were increase or sea grass, increase crabs, lobsters, octopuses, and decrease.

If you need some time to tick or fix your answer you can pause the video and do that now.

Brilliant, okay.

So here's another scenario we could think about we're kind of working our way up the food web here.

We've thought about what would happen if we removed the sea grass to sea urchins.

Now, let's think about what would happen if we removed the crabs, this is a bit more complicated.

Well, if I remove the crabs then maybe the octopuses will decrease because they have less food.

But actually what's more likely to happen is that the number of lobsters will decrease because the octopuses won't have any crabs to eat.

So they have to eat many more lobsters.

And if the number of lobsters decreases, what do you think's going to happen to the sea urchins.

If there's no crabs to eat them and fewer lobsters to eat them, what's going to happen.

The number of sea urchins might increase and then what's going to happen to the sea grass if there's lots more sea urchins eating them? The amount of sea grass is going to decrease.

Can you think about a really similar scenario for me now? So this time, instead of removing the crab let's remove the lobster.

What do you predict will happen? So remember, you can use your food web that you've drawn to help you.

If lobsters were removed from the food web I predict that the number of crabs would mm, the number of sea urchins would mm, and the amount of sea grass would mm.

Pause the video and complete your prediction for me now, please.

Great, good job.

So let's think about that scenario.

If we remove the lobsters, then the number of crabs is going to decrease and the number of octopuses, but the number of sea urchins will increase which means the amount of sea grass would decrease.

Well done if you figured that out.

So this could be another reason why my octopuses are maybe decreasing.

What evidence would I have to look for on my dives in order to see if this was the case.

I'd have to see if the number of sea urchins was increasing.

So if there are a lot more sea urchins and this could be one of the possibilities of what's affecting my number of octopuses.

You can mark your answers with your green pen now.

So the answer was decrease, increase, decrease, pause the video to mark your work now.

Brilliant.

Thank you so much for your help.

That's given me lots to think about different scenarios of why my number of octopuses could be decreasing.

I'm going to hand you back over to Miss Roberts now, who's going to talk to you about the different reasons why an animal might be removed from a food web.

So what's causing what could be causing those different animals to decrease in numbers.

Thanks for your help today, enjoy the rest of your lesson, bye.

So now that we've thought about what would happen to food chains and food webs, if there was disruption, I wonder if we can think about what causes disruption.

So what are the things that may affect the trees or the grass that we've already looked at.

So I'm going to talk you through them.

The first one would be deforestation and this is where lots and lots of trees are cut down.

It's normally for human use, for uses such as resources like building.

Global warming is another factor that can affect a food web.

Can you think why? What happens during global warming? Well done, everything is warming up.

So that means the icebergs might be melting and that's a habitat for some creatures and organisms. So that would be a reason that food web might have to adapt and change.

And pesticides.

Pesticides are chemicals that are used in fields and crops to help things grow in a certain way.

This can be very damaging for the organisms that live there such as insects.

So although they help the crops to grow the insects might be killed.

So if the caterpillars in our food web were killed, that would have affected the birds.

So that is an effect that might cause disruption.

Okay, there are a few more.

Rainfall is another one.

Now this could go two ways.

Sometimes you might have too much rainfall.

In which case, there will be flooding.

What can flooding do to plants and crops in fields team? What would happen if there was too much rain, they might die yes, because they might get swamped, equally they may be not enough rainfall in which case there'll be a drought and that would also kill plants and animals because all living things need water to survive.

So drought would be where the land dries out and there'll be no water left.

The other thing that can affect food webs is humans.

We do a lot of farming and sometimes we like to farm things that we like to eat, but this can be damaging if we farm them too much.

For instance, avocados take a lot of water to be grown.

And this is not natural if we grow them in fields and fields and fields.

So this can cause disruption to food webs where avocados weren't growing before.

Okay, I have a task for you.

I'm going to turn around my visualizer because what I'd like you to do is you've worked so hard this unit that I'm going to give you something nice to do.

I would like you to do the following.

Let me show you.

So in my book, what I've got is I got a bubble and I've written causes of disruption to food webs.

I've done the first one for you, which was deforestation.

Now what I'd like you to do is see if you can remember all of the other causes of disruption to food webs that I've just talked about, making sure you're using your neatest handwriting and using lines coming off your bubble like this.

See if you can remember all of them from memory because it really tests your short-term memory which helps your long-term memory.

If you really can't, then you can go back to the video and watch the rest and jot down your answers once you go through the video.

Let me just turn off my visualizer now that you know what to do.

Okay, so pause the video and have a go at your task now.

Okay, well done everyone.

I'm really impressed with that.

What you need to do is you need to go and re-watch those so that you can have the answers so you can tick yourself.

Or if you want to, you can add in the ones that you've missed.

So well done, everyone.

That is the end of our unit on ecosystems. You are a hero.

You are absolutely amazing, what fantastic learning you've done.

I am so impressed.

And Lenny the lion here wants to give you an awesome cheer.

Because he is also really impressed with your learning.

I hope you've made some useful notes and I hope you've enjoyed learning about ecosystems. It's really important to think about our planets and how we live in it.

So join me again for more science learning, I really enjoyed being your teacher, bye everyone.