Lesson video

Hello, I'm Mr. Jarvis, and I'm gonna be taking you through today's lesson from the unit, maintaining biodiversity, and human impacts.

Today we are looking at examples of human interactions with ecosystems, including fish farming.

By the end of today's lesson, you should be able to describe examples of human interactions with ecosystems, including fish farming, eutrophication, and the introduction of non-indigenous species.

There are four key words to today's lesson.

They are biodiversity, fertiliser, eutrophication, and indigenous species.

You can pause the video at this point if you want some time to read through those definitions for yourself, but we will go through the definitions as we move through the lesson.

Today's lesson is broken down into three parts.

First, we're going to look at fish farming, and animal welfare.

Then we're gonna move on to eutrophication.

And finally, we'll talk about the impact of introducing new species to a habitat.

So if you're ready, let's get started with our first section, which is about fish farming and animal welfare.

As the human population increases, there's an increased demand for food.

And intensive farming methods have been adopted to provide humans with meat.

These methods can keep animals in confined spaces and unnatural conditions.

Not all of the food eaten by farm animals is converted to biomass.

Animals respire to move, and maintain their body temperature.

And so, to improve food production efficiency movement is limited, and the temperature of their environment is controlled.

Therefore, less biomass is used for respiration, for muscle contraction and for keeping warm, and that leaves more biomass available for growth.

So in essence, the animals are eating their food, and it's being converted into more meat, than it would be if they were in natural conditions.

Intensive farming methods can cause some ethical concerns, particularly about animal welfare.

And farmers increasingly balance the welfare of animals with the need for the animals to grow quickly for food.

Here's a check.

The intensive farming of animals often sees animals kept in small enclosures.

Why is this? Is it A, because farmers want to reduce movement to increase the rate of growth.

Is it B, farmers want to increase movement to increase the rate of growth.

Or is it C, farmers want to reduce movement to decrease the rate of growth.

I'll pause for a few seconds, and then we'll check your answer.

(dog barking in distance) The correct answer is A, farmers want to reduce movement to increase the rate of growth.

Well done if you got that right.

Fish are used as a source of protein across the planet, however, fish stocks have been declining.

This is because humans have caught, and eaten more fish than have reproduced, and this is what we call overfishing.

Overfishing can result in species becoming at risk of extinction, and in the UK one example is the cod from the North Atlantic.

There are lots of other examples around the world, for example, the orange roughy in New Zealand can live to 150-years-old, but it doesn't reach reproductive maturity until it's about 27 to 30-years-old.

So if fishermen catch these fish before they've reached that reproductive maturity, they won't have reproduced, and as a result, the population of the fish will decline.

And that's what's happened.

And so the orange roughy has now declined significantly in numbered.

Food webs and food chains can be disrupted, because it impacts other species.

There's not food that's available for those species, because they've been taken out of the ecosystem by humans.

And fewer fish will be available to feed the human population as a result.

For these reasons, it's really important that humans conserve fish stocks.

This has been achieved through sustainable fishing.

And sustainable fishing involves creating marine nature reserves that help to create places for species to reproduce.

They introduce fishing quotas, and these limit the number and the size of the fish that can be caught.

And through making the size of net larger so that younger fish are able to escape through the holes in the net, and go on to reproduce.

So let's move to a check.

Which of the following is an example of sustainable fishing? Is it A, increasing the hole size in nets.

B, decreasing the hole size in nets.

Or C, allowing fishermen to catch fish all year round? I'll pause for a few seconds, and then we'll check your answer.

The correct answer is A, increasing the hole size in the nets is an example of sustainable fishing.

Well done if you got that right.

Here's another check.

Fishing quotas help to conserve the natural fish populations by A, limiting the number of fish that can be caught.

B, reducing the number of days fishermen spend at sea.

Or C, limiting the size of fish that can be caught.

Again.

I'll pause for a few seconds, and then we'll check your answer.

The answer this time is all three answers.

All three answers are examples of how fishing quotas can help to conserve the natural fish populations.

Well done if you got those.

Fish farming has increased across the globe, and this is helping to provide a supply of fish for humans.

The fish are kept in cages they can be in ponds, or they can be as in the picture here at sea, and you can see some of those cages.

The fish are fed high protein food, and that helps them to grow quickly.

The use of fish farms helps to ensure that there are supplies of fish for humans to eat, and they also help to conserve natural fish populations, which in turn helps to conserve biodiversity.

Let's do another check.

How do fish farms help to conserve natural fish populations? Is it A, less fishing helps natural population sizes to recover.

B, more fish are caught by fishermen at sea.

Or C, less fishing means there are less impact on the biodiversity of the oceans.

Again, I'll pause for a few seconds, and then we'll check your answer.

The answers here are A and C, less fishing helps to protect the natural populations and it means that there's less impact on the biodiversity of the oceans.

Well done if you got those.

So let's move to a task.

Fish farms keep large numbers of fish of the same species in cages.

The cages are located in the sea.

Explain why individuals of a species of fish grow more quickly in a fish farm than they would in their natural environment.

You'll need to pause the video at this point, write down your answer, and then when you're ready, press play, and we'll check to see how well you've done.

Good luck.

So I asked you to explain why individuals of a species of fish grow more quickly in a fish farm than they would in their natural environment.

You might have included that the fish cannot move as much, as they live in large nets, and this means that they don't use as much energy from the food, the biomass, that they eat.

And there's more food, there's higher quality food, or more frequent feeding of the fish, so they're able to grow or add biomass more quickly than fish would do in the natural environment.

Well done if you got that correct.

That brings us to the second part of today's lesson, which is all about eutrophication.

So if you're ready, let's move on.

Farmers want to make sure that they maximise crop growth and yield, and this is so that farmers can feed the ever increasing human population.

Farmers add fertilisers to the soil to make sure it stays fertile for a long period of time.

Fertilisers contain all of the mineral ions that plants need to grow well, which include nitrates.

Farmers use both man-made fertilisers and also natural fertilisers, such as manure.

Organic products are grown without the use of man-made chemicals.

Nitrates are minerals that are essential for plant growth, and the plants take the nitrates from the soil using their roots, and they then use those nitrates to help make proteins.

That helps to improve the crop yield, because proteins help organisms to grow and repair.

So here's a check.

Why do farmers use fertilisers? Is it A, to prevent pests from eating crops.

B, to make sure that seedlings germinate.

C, to ensure that soil contains the minerals that plants need for healthy growth.

Or D, to ensure that plants get the water that they need.

I'll pause for a few seconds, and then we'll check your answer.

The correct answer is C, farmers use fertilisers to ensure that the soil contains the minerals that plants need for healthy growth.

Well done if you got that.

Overuse of fertilisers, including organic fertilisers such as manure, can impact environments.

And this is because minerals, particularly nitrates, get washed into rivers and lakes, and that causes algae to grow quickly, and forms a blanket which eventually blocks out the light from the plants that are living underneath.

And without the light, the water plants are unable therefore to photosynthesise and eventually die.

There's a large increase in the number of microorganisms that then have to decompose the dead plants, and these microorganisms respire, and remove lots of oxygen from the water.

And this reduces the oxygen levels, and causes other organisms, such as fish, to die.

And in turn, they are decomposed by microorganisms, removing even more oxygen from the water.

And eventually, the oxygen levels fall so low that the water can no longer support any aquatic animals.

And that's what we call the process of eutrophication.

Eutrophication can be reduced by, using less or targeting the use of fertiliser to prevent nitrates and other minerals from being washed into water.

By constructing areas of wetlands that help us to act as filters, and absorb those minerals from the water that's being washed away, and towards the rivers.

Or by treating affected bodies of water through oxygenation, or removing algae.

And here's a picture of some paddle wheel aerators and pumps that are used to help oxygenate water.

Here's a check.

What causes eutrophication? Is it A, a buildup of pollutants in the atmosphere.

B, the use of pesticides in farming.

C, the use of fertilisers in farming.

Or D, increasing atmospheric carbon dioxide concentration.

I'll pause for a few seconds, and then we'll check your answer.

The correct answer is C, the use of fertilisers in farming is what causes eutrophication.

Well done if you got that.

So here's a task.

Farmers use organic and artificial fertilisers to help them provide enough food to feed the increasing human population.

Fertilisers provide plants with minerals such as nitrates that help them to grow well.

I'd like you to explain why using too much fertiliser can have a negative impact on aquatic habitats.

You'll need to pause the video, write down your answer, and then we'll check to see how well you did.

Good luck.

So how did you find that? I asked you to explain why using too much fertiliser can have a negative impact on aquatic habitats.

You might have included the following points.

Minerals such as nitrates get washed into aquatic habitats, and that can lead to eutrophication.

Eutrophication is where plants, such as algae, grow really quickly.

This blocks out light from plants below the surface, and prevents them from photosynthesising, and eventually those plants will die.

Microorganisms and decomposers break down the dead plants.

These organisms use lots of oxygen from the water to respire, animals in the water then don't have enough oxygen to survive, and biodiversity is reduced.

Well done if you've got some, or all of those answers correct.

That brings us to the third part of today's lesson, which is all about the impact of introducing new species to a habitat.

So if you're ready, let's move on.

Most of the organisms we see around us are what we call indigenous species, and that means that they occur naturally in the ecosystem.

As more humans travel globally, there's been an increase in the introduction of organisms from one part of the world to another.

Here on the screen we've got some of the UK's indigenous, or native species.

Some species are intentionally introduced.

Grey squirrels were introduced into the UK in the late 1800s in many stately homes.

And the grey squirrel is well adapted to live in the UK.

It was able to escape from those stately homes, and outcompete the indigenous red squirrel.

The grey squirrel is an example of an invasive species, a species which outcompetes the indigenous species.

Japanese knotweed was introduced in the UK in the 1850s as an ornamental garden plant.

And the plant grows rapidly from rhizomes, or roots that it produces really quickly in the summer months.

And those roots are so strong that they can damage house foundations.

It's kept in check in its native Japan by a large native ecosystem of vigorous growing plants such as bamboos, grasses, and lots of natural invertebrate species which feed on it.

However, in the UK it outcompetes other species, and that reduces biodiversity in the habitat.

And there's no native species that feed on the plant, and so it grows unchecked.

Chinese mitten crabs are another example of an introduced species.

They're transported by ships, here's a picture of a Chinese mitten crab.

They're native to southeast Asia.

The first UK record was in London in 1935, but they're now found around the UK coast.

The crabs can damage river banks, and outcompete indigenous species.

They also can block water outlets, and damage fishing nets.

The increase in human global travel can have huge consequences for humans' health, food production and biodiversity.

Travel is really important in the spread of diseases, which infect humans or other species.

And half of the emerging pest plants and diseases are attributed to human travel.

Introduced species can quickly become invasive, as we saw with the grey squirrel.

They can spread quickly as a result of having no native predators, no native parasites or diseases, no native competitors that would normally limit their population size.

And here's another example, the red signal crayfish is an invasive species in the UK.

Invasive species can have a large negative impact on biodiversity in a habitat, and some countries have strict laws about introducing non-indigenous species.

So here's a check.

A species which is introduced and outcompetes an indigenous species is called a, A, introduced species.

B, a native species.

Or C, an invasive species.

I'll pause for a few seconds, and then we'll check your answer.

The correct answer is C, it's an invasive species.

Well done if you got that.

That brings us to our final check for today's lesson.

The red signal crayfish was introduced into the UK from America in the 1960s.

And since its introduction, the number of indigenous white-clawed crayfish have declined.

Explain how the introduction of the red signal crayfish may have led to the decline in the white-clawed crayfish numbers.

You'll need to pause the video at this point, write down your answer, and then when you're ready, press play, and we'll check your answer.

So I asked you to explain how the red signal crayfish introduction may have led to the decline in the white-clawed crayfish numbers.

Some possible explanations include that the red signal crayfish are predators of the white-clawed crayfish.

There's competition between two species for the same resources, for example, food and shelter.

And it might be that the red signal crayfish outcompetes the white-clawed crayfish for these resources.

It might be that the red signal crayfish may carry parasites or diseases which have a greater impact on the indigenous white-clawed crayfish species.

All of the above would result in the population of the white-clawed crayfish reducing in number.

Well done if you got any of those answers.

That brings us to the summary of today's lesson.

We've seen that humans can positively interact with ecosystems by protecting habitats, and helping to preserve biodiversity.

Humans though often negatively impact ecosystems, overfishing has significantly reduced fish populations which has reduced the biodiversity of those ecosystems. Farmers use fertilisers, which help to produce food for the increasing human population, but it also leads to eutrophication, which reduces biodiversity.

The introduction of species from other parts of the world has seen some indigenous species outcompeted, and that's reduced biodiversity too.

We've seen that through sustainable methods of intensive animal farming, which include improving animal welfare, and through careful use of fertilisers, human impacts on ecosystems can be reduced.

Thanks for learning with me, as always, during the lesson, and I look forward to seeing you again soon.

Bye-bye for now.