Ecosystems and food webs

  • What is an ecosystem?
  • How often does it rain in a rainforest or in a desert?
  • Now that I know how people eat, how do animals get their food?
  • Why can animals only eat one type of thing - for example why won't a great white start eating kelp or why won't a tortoise hunt a dolphin?

Introducing this topic

Many of the concepts in this unit revise work done in Gr. 5 with the consequence that this unit has taken a different approach: these topics were not dealt with in depth but given a good, clear introduction to revisit and acknowledge existing knowledge and then we move to a stronger focus on environmental problems and permaculture as one of many positive solutions. If at all possible, watch the video clip on permaculture - it is fantastic and inspirational, and makes for far more positive reading than the doom-and-gloom that tends to dominate the media today.

Nothing in the world can live truly on its own. No plant or animal, and certainly no human. Living things are connected to each other, they depend on each other and on the non-living things in their environments.

In this chapter we will take a closer look at ecosystems and examine the different kinds of ecosystems that we get around the world, see how animals, plants and microorganisms depend on each other and learn about food webs and feeding relationships in an ecosystem.

Different ecosystems

An ecosystem is an area where living and nonliving things depend on each other in many different ways. An ecosystem can survive on its own without any help or products from any other sources because the living and nonliving things in the ecosystem depend on each other for their survival.

There are many different types of ecosystems on our planet:

  • rivers
  • mountains
  • sea and the rocky shores
  • ponds and wetlands
  • arctic and alpine tundra are in extremely cold regions close to the North and South poles. There are no trees but some shrubs and dwarf plants grow in wet, spongy soil if it is not permanently frozen (they call this permafrost).
  • grasslands: tropical savannas and temperate grasslands.
  • forests, including tropical rain forests, and forests of coniferous and/or deciduous trees in moderate climates support many kinds of herbivores and carnivores.
  • deserts and semi-deserts

Describing different ecosystems


  1. Below is a table with photographs of different ecosystems. Study each photograph.
  2. In the column next to the photo, identify the type of ecosystem.
  3. Then write a description of the ecosystem where you identify:
    1. some important physical features and structures, such as rivers, mountains, rocks, etc.,
    2. the type of climate you expect where this ecosystem is found, and
    3. the types of plants and animals you would expect to find in the ecosystem and why they might benefit from living in these conditions.


Type and description of ecosystem

Answers: Also assess learner's descriptions in terms of the physical features of the ecosystem and how the plants and animals might benefit from these conditions.

  • wetland/pond: reeds, water lilies, birds, fish in the water, terrapins, etc
  • rocky shore: crabs, mussels, small fish, limpets, sea gulls, penguins, seaweed, etc
  • forest: birds, small buck (red duiker), small mammals (mice), big trees, creepers
  • desert: cacti, grass, other succulents, snakes, small mice, birds
  • river: reeds, trees, fish, birds, otters
  • snow-capped mountains: minimal life - sparse vegetation, mountain goats, snow leopards, rabbits, etc
  • savanna/grassland: grasses, a few trees, birds, small rodents, game (ie. buck, leopards, zebra, etc)
  • coral reef: coral, seaweed, tropical fish, turtles, dolphins, crustaceans, anemones, etc

Aunique South African ecosystem

South Africa's fynbos region is unique - it produces an incredible array of plants and specifically flowers. Our national symbol, the Protea, grows wild here - and NOWHERE else in the entire world!

The King Protea, our national flower
Typical fynbos at Cape Point Nature Reserve
A fire passed through this fynbos area near Kleinmond, Western Cape. A year later the indigenous fynbos had regrown but the pine trees that are not indigenous were all dead.

South Africa is famous for its fynbos - it does not grow naturally anywhere else in the world! Fynbos plants are especially adapted to survive the climatic conditions and frequent fires. The low bushes can survive the harsh windy conditions and the plants produce seeds that can very often only germinate once they had been scorched by fire.

The Fynbos biome in South Africa has a huge biodiversity in plants and animals.

Living and non-living things in ecosystems

In an ecosystem, there are certain relationships between the living things and the non-living things in a particular area.

A healthy ecosystem is one in which there is a balance between the non-living and living things. a healthy ecosystem also depends on sufficient biodiversity of plants, animals and their habitats.

We saw at the beginning of the term that plants depend on air, water and sunlight in order to make their food. Do you remember what this process is called?!

What are some of the non-living things in an ecosystem?

air, sunlight, water, soil

What does biodiversity mean?

Biodiversity refers to the variety in the species of organisms (plants and animals) in a given habitat.

Animals also depend on the non-living things in their ecosystem. All animals need to breathe (oxygen from the air around them) and they need to drink water. Some animals also use the non-living things to make their shelters. For example, ants rely on the soil and sand to build their nests in.

Assessing the balance between living and non-living things


  1. Look at each of the following photographs of different ecosystems in which the balance between living and non-living things has become upset.
  2. Answer the questions on each picture.
A dried river bed.

In this river ecosystem, the water has dried up due to a drought. How does this affect the biodiversity of the plants and animals in this ecosystem?

Many animals which relied on the water as their habitat would have died, such as fish, frogs, etc. In turn the birds which ate these animals would have left. Plants which relied on very moist soil would have died, such as reeds and water lilies.

However, many of these ecosystems also have animals adapted to dry seasons (fish and amphibians go dormant, elephants dig for water). Although, long periods of drought are still detrimental to these animals.

The soil has started to erode.

In this photograph the soil has started to erode. Why do you think this happened?

This may be a difficult question to answer. It could be because the land was farmed and so the naturally occurring plants were removed. There are now no roots holding the soil together. When the rain comes, it washes the soil away causing erosion.

A pine tree plantation

In this man-made forest, there is not much life under the canopy of the trees. Why do you think this is so?

This is because the trees block a lot of the sunlight which plants and animals need, so they do not live there. Also, the pine trees use a lot of the water in the ground, meaning there is not much left for other plants.

As you have seen from this activity, the living things depend on the non-living things in an ecosystem. There is also a very fine balance, and if something is upset, then the ecosystem will begin to deteriorate.

The importance of water in an ecosystem

Without water life as we know it cannot exist.

Animals depend on water in their ecosystems
  • Water provides a habitat for many different organisms and allows plants and animals to survive and breed.
  • Water is a universal solvent and allows important chemical reactions to take place. It is a key ingredient for photosynthesis where plants create glucose (sugars) from sunlight, water and carbon dioxide.
  • Water plays an important role in plant reproduction as some seeds need to be dispersed by water. (Try and remember which seeds get dispersed by water?)

Food webs

We have now learnt what makes up an ecosystem. We now know that there are relationships between living and non-living things. In an ecosystem, plants and animals are also connected to each other due to their feeding relationships. The plants in an ecosystem are called the producers and the animals are the consumers.

Do you remember what a producer and a consumer does in an ecosystem (from Gr. 5 work but also from the photosynthesis work you started this term with)? Write an answer below.

A producer produces food through photosynthesis from sunlight, water and carbon dioxide while a consumer cannot produce its own food and therefore eats the producer or other consumers.

There are different types of consumers:

  • herbivores only eat plants and plant products.
  • carnivores only eat meat and meat products (eggs).
  • omnivores eat plant and animal products.
  • insectivores only eat ... can you guess what?
  • scavengers eat dead animal matter.
  • decomposers are microorganisms like bacteria and fungi, as well as mushrooms, that break down animal and plant material into tiny particles and recycle it into the ground ready for the plant to use.

What do you call a human herbivore?


Do you remember in Gr. 5 when we looked at food chains? Here is an example of a food chain:

A simple food chain

Turn to a friend and design your own food chain consisting of four organisms. Remember a food chain always starts with plants (producers) and ends with scavengers or decomposers.

In a whole ecosystem, the feeding relationships between plants and animals are much more complex than a simple food chain.

In the above food chain, for example, the chameleon might also eat flies or butterflies, the snake does not only eat chameleons, but also lizzards and mices, and the mongoose also eats small birds and eggs.

So what is a food web?

When we put many different food chains in an ecosystem together, we get a food web.

A food web consists of many thousands and thousands of food chains that are connected to each other.

Below is a food web in a savanna ecosystem.

A food web in a savanna

There are also different levels of consumers in an ecosystem:

  • Primary consumers are the herbivores which eat the plants, such as the mice and grass in this savanna food web.
  • Secondary consumers eat primary consumers.
  • Tertiary consumers eat the secondary or primary consumers.

Study the food web and identify the producers and the consumers. Distinguish between the primary, secondary and tertiary consumers. You can write your answers (in pencil in case you make a mistake) on the food web illustration.

Below is another food web consisting of plants, fish and birds. What kind of ecosystem do you think this food web describes?

A food web consisting of plants, fish and birds.

Aquatic - wetland, river, lake, pond, etc

Drawing food webs


  1. Use the following lists of organisms in a sea and forest ecosystem to draw a food web for each ecosystem.
  • Sea ecosystem: phytoplankton, sea weed, zooplankton, crab, lobster (scavenger), prawn, small fish, large fish, turtle, seal, dolphin, killer whale.

  • Forest ecosystem: grass, small plants, seeds, beetle (herbivore), butterfly, tree frog, rabbit, mouse, seed-eating bird, insectivorous bird, snake, fox, owl.

Now that we have learned about the living and nonliving things in an ecosystem, and the relationships that exist, let's investigate an ecosystem in or near the school.

Woohoo! I love going outside to study the world around us! Come on, let's go!

Studying an ecosystem

For this activity, the teacher can identify some possible areas in or near the school before the lesson. Then when it comes to the lesson, time is not wasted finding appropriate spots. learners can either all study the same spot, or there can be several spots covering different ecosystems. Encourage learners to take notes on their scrap paper and clipboards whilst they are outside to practise their observation and note-taking skills.


  • 8sticks
  • string (about 30 m)
  • clipboard
  • scrap paper
  • pen and pencil
  • reference books for identifying species names


  1. You will work in groups for this activity.
  2. Go outside with your teacher and identify an ecosystem in your school grounds, or near to the school which you can study
  3. You will need to mark out the area with the sticks and string using the quadrant method.
  4. Look at the picture below to get an idea of how to set up your quadrants.
  5. The area must be about 5m x 5m.
  6. Once you have marked out the square, divide it up into 4 smaller squares with the string so that you have a quadrant with 4 squares as shown in the picture.
A 5m x 5m quadrant
  1. When marking out your ecosystem to study, be careful not to damage any of the plants and animals that are there as this is what you will be studying.
  2. For each of the 4 quadrants in your ecosystem, count the number of different species of plants and animals.
  3. See if you can identify the names of the different plant and animal species using reference books. Fill this out in the table below when you get back to class.
  4. Study the non-living things in your ecosystem. For example, what type of soil is present? Are there any rocks? Is there perhaps a stream running through your ecosystem? What is the sunlight like, shady or full sun? Are there any animal shelters present? Make notes about this as you will have to answer questions when you get back to class.


  1. What type of ecosystem are you studying?

    Activity-dependent (ie. grass ecosystem, stream/river ecosystem, forest ecosystem, etc)

  2. What is the total area of your square?

    Dependent on learner's square, but if the square had 5m sides, then the area is 5mx5m = 25m.

  3. Fill out the table below for each quadrant:

Quadrant 1

Quadrant 2

Quadrant 3

Quadrant 4

Number of plant species

Number of animal species

Total organisms in each quadrant

  1. What is the average number of plant species in the whole square? (Hint: To work out the average, add up the number of plant species for each quadrant and divide by the number of quadrant).

  2. What is the average number of animal species?

  3. What is the average number of total organisms in your ecosystem?

  4. What is the number of organisms per unit of area? This is quite tricky - your teacher might need to help you!

To work out number of organisms per unit area, divide the total number of organisms by the total area of the square. The answer will be in number of organisms/m2. Do this calculation on the board for your learners to see and then repeat with their own numbers.

  1. Fill in the names of 3 species of plants and 3 species of animals that you identified in the table below. Do a simple drawing of each organism and write a short description of each species.

Names of species



Plant species:




Animal species:




  1. Write a description of the non-living things in your ecosystem. Explain the availability of food for the animals, the water availability, the type of soil (sandy or rich organic, soil, for example) the amount of sunlight (shady or full sun for example), and describe if there are any natural shelters for animals.

Encourage learners to investigate and explain some possible reasons for observed phenomena, for example, presence of a particular insect, colour of soil, presence of a certain type of plant, etc.

  1. Your ecosystem will contain animals and plants which are interdependent and they are connected by their feeding relationships. Use the space below to draw a food web for your ecosystem.

  2. Ecosystems are often destroyed due to the impact of humans or other environmental disasters, such as a flood or drought. Identify some possible threat to your ecosystem and write about them below and why they could destroy your ecosystem.

  3. Brainstorm possible ways to prevent these threats to your ecosystem from destroying it. Record your ideas below.

  • There are different ecosystems where living and nonliving things depend on each other.
  • Living and nonliving things share an ecosystem.
  • Food webs show how plants and animals are connected by their feeding relationship.
  • Plants are producers of their own food.
  • Animals are consumers and eat plants or other animals.
  • Microorganisms are decomposers and break down dead plant and animal material and return the nutrients to the soil.

Provide a definition for an ecosystem.

An ecosystem is an area where living and non-living things depend on each other in many different ways. It consists of all the organisms and their habitats in a given area.

Why do you think the feeding relationships between plants and animals in an ecosystem is called a food web?

This is because when you draw all the links in between all the organisms, it looks like a spider's web as each organism has multiple relationships with other organisms.

What is the term given to animals which break down dead plant and animal material?

Decomposers (microorganisms)

Read this blog entry made by a Gr. 6 pupil in Limpopo province reporting on their environment.

"I live in the Waterberg area in north Limpopo province. This is the first area in South Africa to be named a biosphere reserve. During the Stone Age indigenous people lived in this area. They brought in cattle that overgrazed the grasslands and caused a terrible outbreak of tsetse flies. Then in the 1900s Dutch farmers brought in more cattle. All the cattle, goats and sheep of the Dutch farmers and the indigenous people almost destroyed the natural bushveld vegetation.

Luckily the people realised the problems in time and started to reintroduce and protect original species of animals and plants to the area. White rhino, giraffe, hippopotamuses and different species of antelope and smaller buck returned. Ecotourism is now very popular and farmers try really hard to stop soil erosion, and to introduce original grass species. Farmers also started to take away fences between their farms to allow animals to walk free."

Described what happened to the land when all the cattle, sheep and goats were grazing on it.

The animals over-grazed the land which means most of the natural vegetation was eaten and did not have enough time to regenerate, so the soil was left without protection and started to erode.

Explain what happened to the original, indigenous animals that lived on the land after the cattle farmers arrived?

Because the original animals could no longer find the natural vegetation they were used to, they either starved or moved out of the area.

Can you predict what would have happened if the people did not change the way they used the land?

The land would become a barren and desolate place with no vegetation left, which means very little rain will also fall there. The precious topsoil would erode and the landscape would become a desert.

What factors did they have to change to protect and conserve their land?

They removed the many cattle herds that were over-grazing and replaced them with the original animals that used to live in that area. They also replanted the natural, original plant species that grew well in that area to provide food for the animals. They then advertised this area as a eco-friendly tourist attraction and made lots of money from tourists rather than from destroying the countryside.

If the farmers instead of removing the cattle and goats, rather planted crops on the land, what do you think would have eventually happened?

The soil would probably not have sustained the crops for many years, so the farmers would spray lots of fertilizers and probably poisonous pest controls which would have further destroyed the environment.

What choices do you need to make or what do you need to change or improve in your community to stop similar types of environmental destruction from happening there?

This is context specific but learners need to show evaluation and creative problem solving skills to come up with good suggestions to save their own communities.