Lesson video

Hello geographers.

My name is Mrs. Griffiths and today, you and I are gonna be thinking about and how to understand small-scale ecosystems. So this gives us the opportunity to understand the interactions between different components within a small-scale ecosystem, thinking about living organisms, how they interact with each other, and also with their physical environment in which they live.

So if you're ready, let's get started.

I can understand the natural processes that occur within a small-scale ecosystem in the UK.

So that's what we want to be able to say by the end of the lesson.

We have some keywords today, and they are as follows: ecosystem, producer, consumer, food chain, and decomposer.

So an ecosystem is defined as a community of organisms such as plants and animals that interact with one another and their non-living, abiotic, environment.

A producer is an organism that's able to absorb energy from the sun through photosynthesis.

A consumer is an organism that gets its energy by feeding on other organisms, animals, and/or plant matter.

A food chain represents the connections between different organisms, plants, and animals that rely on one another for their source of food.

And a decomposer is an organism such as a bacterium or fungus that breaks down dead plant or animal tissue or waste.

So those are some of the keywords that we are gonna be using throughout the lesson.

Okay, so thinking about the lesson outline today, first of all, we're gonna be answering this question, what is an ecosystem? And then secondly, thinking about what processes occur in a small-scale ecosystem.

So let's start on this first question.

What is an ecosystem? Now, here, we have a photograph for you to study.

An ecosystem, as we've heard, is a community of organisms such as plants and animals that interact with one another and they're non-living environment.

But if you take a closer look at this photograph, it's a place called College Lake in Buckinghamshire in the southeast of England.

And it's a nature reserve.

What might be the living, or biotic, and non-living, abiotic, components of the ecosystem in the picture? Let's zoom in a bit so we can really see what's going on in that picture.

Now, I'm sure you spotted these plants in the foreground.

We can see trees, we can see grasses.

I imagine there are flowering plants perhaps on the island and some mosses growing.

But also, in terms of the living components here, we have animals, birds, insects, fish, amphibian and mammals, but also microorganisms that we can't see, but we can assume are here in this place.

Bacteria and fungi.

What about the abiotic components? These are the non-living components of this environment.

So we have the chalk bedrock and the shallow soil that's found over that chalk created by the weathering of the rock, and you can actually see in the photograph the very white cliffs.

So we can actually see that chalk in the picture.

We've also got the water in the lakes and the climate made up of the sunshine and the rainfall.

And these are all abiotic components of this small-scale ecosystem, this aquatic and grassland environment.

So College Lake is home to 1,000 different species.

Do you think the Canada geese, pictured here, are biotic or abiotic components? Pause the video and have a quick think.

Lucas says, and he's absolutely right, "They are biotic, we can see them feeding!" And you'll remember that nutrition or feeding is one of the key components of living organisms. So there's a good check for you and well done if you've got that one right.

Here's a different photograph also at College Lake.

There are some small ponds on the nature reserve site, but I want to check your understanding again.

Is pond water biotic or abiotic? What do you think? Well done.

I'm sure you agree with Laura.

You have told us that the pond water is abiotic, but, as sort of different points here, there are living things in it.

And Laura's point here, which I no doubt you said as well, well done, links to our theme for the day, really, where we're thinking about the interactions between biotic and abiotic components of small-scale ecosystems. Okay, so here's a practise task for you.

I want you to think about this carefully.

College Lake is a tiny natural place where you'll find lots of living things in a non-living countryside.

Now, that's not a very geographical statement.

It's not really using the correct geographical terminology.

Can you rewrite it using the following terms: biotic, ecosystem, abiotic, and small-scale.

So I'd like you to have a go at rewriting that using those terms. Okay, now, well done having a go at that task.

It wasn't very easy.

Let's see what you've got and let's see what we have as an answer.

So Izzy has given us an answer.

Now, she's rewritten that sentence using those terms. Let's have a read of it.

"College Lake is a small-scale ecosystem made up of biotic and abiotic components.

Both the chalk bedrock and soil are abiotic, while the geese and grass are biotic components." Now I'm sure you have something close to that or perhaps even better.

So well done on tackling that tricky task using these new keywords.

And let's move on with the lesson.

Now we've thought about what is an ecosystem, but the question now is what processes occur in a small-scale ecosystem? So what processes occur in a small-scale ecosystem? So we're thinking about those interactions.

Producers can absorb energy from the sun through photosynthesis.

And we have a photograph here of algae.

So this is a green algae that can photosynthesize and here in a pond environment, that's our producer at College Lake.

Consumers get their energy by feeding on other organisms, animals or plants or both.

And we've got a couple of examples here.

So we've got a dragonfly, they're pictured, insect, and a hobby, which is a bird of prey.

And they're both consumers so they can't photosynthesize.

They're getting their energy by feeding on other organisms, plants, or animals.

So we've got production and we've got consumption, I suppose, as our processes.

Now let's have a think about a food chain in the wetland ecosystem at College Lake.

Algae is a producer here and it's eaten by midge, the larvae of midge, plural being larvae.

Those larvae are eaten by tadpoles.

So this is all in the pond water in the lake.

The tadpoles are eaten by dragonfly nymphs, so still in the water, but as the dragonfly nymph becomes an adult and leaves the pond water, the hobby, that bird of prey, feeds on adult dragonflies.

So this is a real food chain in this wetland ecosystem at College Lake.

We can see how energy is transferred up the food chain, from algae to the midge, to the tadpoles, to the dragonflies, to the hobby.

So check for you here.

What's wrong with this food chain? Have a quick look, pause the video, talk to your partner about it.

That's right.

I'm sure you noticed, the arrows go the wrong way round, but why should the arrows go the other way around? Can you explain that? Pause the video now and tell the person next to you.

Absolutely right.

If you've said something about the fact that the flow of energy starts from the producer, in this case, it's the algae, then it flows to the midge, onward to the tadpole, and up the food chain to the dragonfly and eventually the hobby, you are absolutely right.

Well done.

Second check for you here.

What is the producer in this wetland food chain? Pause the video and then restart it when you think you know the answer.

I'm sure you said algae.

Of course, the algae is the producer.

It's green as the green chlorophyll that allows it to photosynthesize to feed the other organisms in this food chain.

Now, College Lake is home to wetlands and chalk grasslands.

Here's an example of a chalk grassland food chain at College Lake.

Let me reveal it for you.

So it starts with bird's foot trefoil, which is a type of flowering plant, which the common blue butterfly, the caterpillar of the butterfly, feeds on.

And we can see the the butterfly caterpillar in the mouth of that bird perched on the branch.

Now, the caterpillar feeds the bird, which, in this case, is blue tit, but the blue tit is eaten by a sparrowhawk, another bird of prey.

And notice with this food chain that there is a primary consumer, a secondary consumer, and a tertiary consumer, all in addition to that producer, the bird's foot trefoil.

Okay, check for you here then, which is the primary consumer in this grassland food chain? Which is the primary consumer in this grassland food chain? Take a look at it closely, pause the video and then restart it when you're ready for the answer.

And if you said B, caterpillar, you are absolutely right.

So that is the primary consumer in this food chain because it's the living organism that feeds on the producer.

Okay, now, as we know, the real world is quite a complicated place.

And interestingly, the dragonfly connects the wetland and the grassland food chains that we've looked at.

So we've looked at the way animals interact within a wetland environment at College Lake, and we've also looked at the food chain for the grassland environment that is around the lakes.

But actually the dragonfly connects those two food chains in two ways.

So as a nymph, it feeds tadpoles in the pond, and as an adult, it preys on butterflies.

So it's actually involved in both food chains.

It starts to give us a sense of the way that the real world is quite a complicated place, even in a small-scale ecosystem.

And it's also true that the bird's foot trefoil, the producer in that grassland ecosystem, is a producer feeding many different animals.

So we have to think about the complexity of the real world.

Those animals include butterflies, moths, grasshoppers and bees.

So real-world small-scale ecosystems still have a huge complexity to them, okay? In every ecosystem, food chains are connected within a complex food web.

Let's have a look at a food web, then.

Here's an example of food web in a temperate deciduous woodland.

And here we can see a bit like I was describing with that bird's foot trefoil, flowering plant being eaten by a number of different organisms, that grass is feeding more than one group of animals.

Similarly, while flowers and fallen oak leaves are feeding both the worms and the snails.

In this food web, we can see there are primary consumers.

There's one secondary consumer there in the case of a thrush, and we've got apex predators, another term for these tertiary consumers, the fox and the buzzard.

This is a different diagram.

I'm gonna build up stage by stage for you.

Here we've got plant material, or leaves, eaten by butterflies, eaten by blue tits, eaten by sparrowhawks.

So this is a different way of representing the links between groups of organisms in an environment.

And what you can see is each trophic level or position within the food chain is represented by a bar that is drawn in proportion to the amount of material there.

Oh, and we can see that there are some decomposers involved in this ecosystem as well.

And I'm gonna talk about those more in a little moment.

But notice how we've also got the number of leaves or animals at each trophic level within this food chain.

Isn't it interesting the number of plant leaves that are needed to feed enough butterflies to feed enough blue tits to feed a single sparrowhawk? So what's going on? What's going on within this food chain? So here's our diagram of the different trophic levels within a food chain.

The weight of biomass gets smaller as energy is transferred up the food chain.

But have you ever wondered why this is? Well, there are a number of different reasons that energy is lost between each trophic level, the first being that animals use energy moving around.

As they move around to find food, for example, butterflies flying around, they're expending energy and that energy is not going to be available to their predators, such as the blue tits.

Energy is used in respiration, so if we think about some of the basic bodily functions that organisms have to keep going to maintain their health, those are using energy.

And thirdly, some of the energy stored in an animal's body is simply not available to predators, such as its skeleton.

Why is this? Well, as Laura says, "Predators don't digest," rather, they can't, simply can't digest the bones.

And that's true for most predators.

Quick check for you.

Which two of the following explain why there are fewer sparrowhawks than blue tits in a grassland ecosystem? Say that one again.

Which two of the following explain why there are fewer sparrowhawks than blue tits in a grassland ecosystem? Have a read of the answers and then pause the video.

Once you are ready and you know the answer, restart it.

Okay, so we're looking for two correct answers here.

And the two that are correct are A, some of the energy is lost between each trophic level and B, respiration is a process that uses energy.

Well done if you got that right.

I'm sure you did.

Okay, so we've been talking about the transfer of energy within an ecosystem, but we also need to think in terms of nutrients.

So nitrogen or carbon, these elements are moving between producers, consumers, decomposers within an ecosystem.

And this natural system of movement of nutrients can be represented if we think about three stores of nutrients.

So the first store I want to talk to you about is the biomass, that is, living material, living organisms. Litter, dead organisms such as leaves.

So we're talking about leaf litter, nothing to do with crisp packets, and soil.

So that's the third store in this natural system for nutrients.

And we can represent it in a diagram here.

So I'm gonna use circles for the stores.

So biomass, litter, and soil.

And of course, we've got processes that link these three stores, 'cause I've told you that nutrients are cycling between these through stores in a natural environment.

How does that work? Well, these nutrients are cycling by different processes.

So we've got a process called littering, which is when leaves fall from trees in autumn when there's less moisture around, there's less sunshine.

So trees will drop their leaves and that forms litter on the floor.

We've also got the breakdown of that litter and the processes that releases those nutrients into the soil is called decomposition.

And then we have plant uptake.

So nutrients are taken up from the soil to the biomass.

So how might that work? So for example, plants taking nutrients from the soil as they grow, leaves then fall to the floor, adding nutrients to the litter store.

But then we need this process of decomposition.

We'll break the leaves down and add nutrients to the soil so that soil is rich with nutrients, ready for plant uptake all over again.

Ah, now, what are these fungi doing in the picture? Fungi here are decomposers that help with nutrient cycling.

They break down dead plant and animal matter and waste such as faeces, meaning these nutrients are available for reuse.

So here we can see fungi actually living in the leaf litter.

So decomposers are involved in this process by directly absorbing nutrients by living in or on organic matter.

So this is dead plant material, leaves, branches, we've talked about animal faeces, bones.

They're actually absorbing nutrients by living in or on that organic matter.

And that process returns nutrients to the soil in the form of an organic substance called humus.

Okay, so that's a really important process.

We need to remember that's going on in all small-scale ecosystems. Can you complete the following sentences? Fungi and bacteria breakdown something.

This process of decomposition returns something.

So pause the video, have a talk to your partner.

Think about how we would finish those two sentences.

When you think you have an answer, restart the video.

Okay, so what answer did we have? Fungi and bacteria break down, for example, dead leaves, in the litter store.

This process of decomposition returns, what does it return? It returns nutrients to the soil store, ready for plant uptake.

So if you remembered all of that and you can talk through those arrows on that diagram, congratulations, you are on it today.

So we talked about the way nutrients cycle between those three stores.

It's also worth knowing that there are processes that add nutrients to the ecosystem.

And these are known as inputs.

So for example, we've got rainwater washing nutrients out of the atmosphere either as particles in the atmosphere or dissolving gases in the atmosphere and just adding those nutrients to the litter store.

We've also got the example of weathering.

So weathering is a process that releases nutrients from the bedrock that is below the soil and it actually releases nutrients that form the soil itself.

There are also losses from the system such as runoff and leaching, which I'm going to talk through in a moment.

But first, inputs.

So examples of inputs.

Rainwater washing chemicals out of the atmosphere, but also weathering, releasing chemicals from the bedrock.

Non-examples of inputs, well, uptake by plants.

That's not an input to this system.

It's part of the cycling.

Losses in runoff.

That's a loss.

It's not an input, it's an output.

Okay, so true or false for you to check you listening on this one.

Leaves transfer nutrients directly from the biomass store to the soil store.

So leaves transfer nutrients directly from the biomass store to the soil store.

Is that true or false? Pause the video and then restart it when you think you have an answer.

Now, that's not true, but can you explain why? Have a think.

Pause the video and then restart it when you have an answer for me.

Perhaps you said something like this.

Organic matter is transferred to the litter store, not directly to the soil store.

So leaves, when they fall from trees, are transferred to the litter store, they fall onto the leaf litter and form part of that leaf litter that is on the forest floor, for example, or on the floor of the grassland.

It's not directly in the soil store.

We're going to need the process of decomposition to actually release those nutrients to the soil store.

Back to this idea of losses.

So I was going to just tell you a little bit more about runoff.

Runoff is the loss from the system and it's when water flowing over the ground takes nutrients from the litter.

And that might be as particles, particles of branches, particles of leaves.

We've also got the process of leaching there.

Leaching is where nutrients are removed as water flows through the soil.

So rainwater infiltrates into the soil and it might dissolve nutrients in the soil itself.

And those are lost as that water then percolates into the rock or is lost to the soil and into the river.

So runoff and leaching, these are losses from the system of this small-scale ecosystem we're talking about.

Quick check then.

True or false? Leaching and runoff are examples of inputs into the nutrient cycle of a small-scale ecosystem.

Is that true or false? And if you said false, you'd be absolutely right.

But of course, I'm gonna want you to explain your answer.

So pause the video and restart it when you have an answer for me on that.

Okay, now our answer here was that leaching and runoff are examples of losses, sorry, from the system.

They're losses, they are not inputs.

So if you said something like that, and I'm sure you probably had a slightly smarter answer than the one we have on the screen, congratulations.

Well done.

Okay, so we have some practise tasks for you now.

Let's have a look at the first one.

It says complete the table below using the food web or woodland ecosystem to show the links within a single food chain.

So we've got to pick out a producer, a primary consumer, and a secondary consumer that are linked in a single food chain.

Pick that out from this complex food web.

Our second task is we need to give an example of an organism not shown in that same food web that might decompose fallen oak leaves.

So that's something else we're gonna need to think about.

Give an example of an organism not shown in the food web that might decompose fallen oak leaves.

You maybe have an idea already on that one.

So our next task is going to be Question 3, which asks us to use the words provided to complete these sentences.

Let's have a look at the first one.

A says blank is an input.

It adds nutrients to an ecosystem as the local bedrock breaks down in situ.

Now, what could go in that blank space? Well, we have a box at the bottom with six words that you can choose from to finish off that introduction to what an input is within an ecosystem.

So we've also got B and C to have a look at there.

So I'm gonna give you a chance to have a read through those and work out what you are doing in a moment.

And then Question 4 asks us to describe what is meant by nutrient cycling.

So as geographers, when we talk about nutrient cycling, can you describe that process in some detail? Telling me a little bit about what happens within that process, within a small-scale ecosystem.

So we've got a number of tasks there.

You're gonna need to pause the video and take some time to reflect on what we've learned and have a go answering those.

I know you can do it.

So have a go, pause the video now, and then click Play again when you want to hear the correct answer.

Okay then, how did we get on? Those were four tough tasks, weren't they? So let's have a look at this first one, complete the table below using the food web of a woodland ecosystem.

What did you pick out? We picked out producer as grass eaten by a mouse, which is a primary consumer within this food chain who, in turn, is eaten by the fox as the secondary consumer.

But you might have a different answer.

Secondly, we were asked to give an example of an organism not shown in the food web that might decompose fallen leaves.

I wonder what you said on that one.

We said fungi or bacteria.

So we've actually given two answers there and we were only asked for one, but that hopefully helps you out.

How did you get on there? Question 3.

We need to complete the sentences.

So here are the completed sentences.

Weathering is an input.

It adds nutrients to an ecosystem, as bedrock breaks down in situ.

Rainwater dissolves mineral compounds in the atmosphere, adding them to the ecosystem also.

C was, However, nutrients are lost from the soil store via process known as leaching in which soluble minerals are removed as rainwater percolates into rock beneath the soil.

This is an output from the system.

So you can see the correct terms you need to use to complete those sentences, and if you've got all of that right, you are doing brilliantly.

You are doing brilliantly with this topic.

Don't worry if there's one in the wrong place, you've got an opportunity to correct that now.

Lastly, you were asked to describe what is meant by the term nutrient cycling.

Your answer might include these points.

Plants and animals depend on nutrients in their food.

Within an ecosystem such as a chalk grassland, dead organic matter, e.

g.

, grasses and flowering plants, lose their leaves, which rot down and release nutrients back into the soil with the help of decomposers.

This means that other plants can take up these nutrients via their roots to help them grow leaves.

This cycle repeats ongoingly.

So the whole process is kind of described in that answer there, isn't it? And I'm sure you've done something similar.

I wanted to just show you something else, which was Laura's answer to this.

It's a little bit shorter.

Let's have a look at that.

"A set of physical processes that together form nature's recycling system, enabling the reuse of nutrients in dead and waste material by other living things again and again." So nature's recycling system, I like that phrase.

Well done, all this work you've done today.

We've covered a huge amount of ground, haven't we? Let's think about what we've done in summary then.

An ecosystem is a natural system in which plants and animals and their non-living environment interact.

Producers, consumers, and decomposers are linked in food chains.

College Lake is an example of a small-scale ecosystem in the UK, which includes aquatic and grassland food chains.

Food webs helps us understand the interrelationships within a small-scale ecosystem.

And then nutrient cycles show how nutrients transfer between different stores in an ecosystem, e.

g.

, via littering, decomposition, and then finally, plant update.

So we've covered a lot of ground there and I wanted to say congratulations.

I think you've worked really hard today and well done.