6.1 All organisms are interdependent

Learning intentions

By the end of this topic, you will be able to: • define producer and consumer and identify examples of each • construct and interpret food chains and food webs.

Interactive 6.1 Food chains

food chain a diagram that shows who eats whom in an ecosystem, and how nutrients and energy are passed on Leaf litter

Springtail

Wolf spider

Centipede

Key ideas

• Scientists use a food chain to show the flow of food and energy in an ecosystem. • Producers are found at the start of the food chain. • Consumers need to gain their energy from other organisms. • Food webs have many interlinking food chains.

Food chains A food chain is a way to show the direction that nutrients and energy ow between organisms. It consists of a chain of arrows that always points from the food to the animal doing the eating. For example, a centipede eats a wolf spider. This means the arrow points from the wolf spider to the centipede (Figure 1). The wolf spider provides the centipede with energy to grow and move. Wolf spider Centipede Currawong Figure 1 A simple food chain Plants and plant-like organisms are always found at the start of food chains because they only need air, water, sunlight and a few trace minerals to live and grow. These organisms are known as the producers of the ecosystem. Most producers convert light energy from the Sun into sugars (stored chemical energy). These sugars are known as biological molecules and are stored in the leaves, stems and roots. Animals cannot use the Sun’s energy in this way. They are consumers and must eat other organisms to get the energy they need to survive. They use this energy to stay alive – to pump their blood, to move their muscles and to operate their nerves. The rst consumers in a food chain are also referred to as rst-order (primary) consumers .

In Figure 4 the mountain water skink is a rst-order consumer because it eats plants. Because the noisy miner bird eats a rstorder consumer, it is called a second-order (secondary) consumer . The feral cat eats the second-order consumer and becomes a thirdorder (tertiary) consumer . Most food chains only have four to ve organisms in them. This is because only some of the energy is stored in the consumers. The rest is converted into heat and movement by the organism. Food webs Most animals, including humans, will eat more than one type of food. This can be represented in a food web , which shows several food chains intertwined. Some consumers will have several labels, depending on their eating habits. Figure 5 shows a food web in which there are four different producers. In this example, the mouse can be considered both a primary and secondary consumer because it eats a producer (wheat seeds) and primary consumers DRAFT (snail and beetle). In this food web, the snail is only a primary consumer because it only eats producers (the trees). Food webs show how every living thing in the environment needs every other living thing to survive. When people talk about the ‘web of life’, they are referring to the interactions between all living things.

Currawong

Figure 2 An example of a backyard food chain Producer First-order consumer Second-order consumer Third-order consumer

Same as

Producer Primary consumer Secondary consumer Tertiary consumer

Figure 3 A food chain starts with producers, such as plants, and moves through several orders of consumers.

Berries and fruit

Mountain water skink

Butcher bird Eagle Snake

Mouse

Noisy miner bird

Feral cat

Figure 4 A food chain showing the feral cat as a thirdorder consumer

producer a plant or plant-like organism that is at the start of food chain because it produces its own food, usually using sunlight consumer an animal that can't convert the Sun's energy into sugars and instead must eat to get the energy it needs to survive

Retrieve 1 Identify where producer plants get their energy. Comprehend 2 Describe how the direction of arrows in a food chain is decided. Analyse 3 Contrast food chains and food webs. 4 Examine the food web in Figure 5. a Identify an animal that is both a secondary and a tertiary consumer. b Classify the type of consumer of the snake in this food web.

6.1 Check your learning Apply 5 Imagine that you were asked to nd out how many different types of animals lived in your backyard or local park.

Discuss how you would go about nding this out. (HINT: Would it be possible to individually count them all?) 6 Construct your own food web of organisms that you would nd in the local park. Correctly identify the producer and all the consumers.

Spider Sparrow Grasshopper

Caterpillar Grass Thistle Wheat seeds Tree Figure 5 A food web shows the extended relationships between various organisms. rst-order (primary) consumer an organism that eats only producers such as plants, algae and bacteria; it does not eat other consumers second-order (secondary) consumer a carnivore that eats primary consumers third-order (tertiary) consumer a carnivore that eats primary and secondary consumers and is therefore at the top of the food chain food web several intertwined food chains, showing the extended relationships between different organisms

Beetle DRAFT Snail Quiz me Complete the Quiz me to check how well you’ve mastered the learning intentions and to be assigned a worksheet at your level.