8.2 All organisms have a role in an ecosystem

In this topic, you will learn that:

• animals that only eat plants are called herbivores • animals that only eat other animals are called carnivores • animals that eat both plants and animals, like many humans, are called omnivores • decomposers obtain energy by breaking down dead organisms.

Video 8.2 Ants and caterpillars

herbivore an animal that eats only plants

carnivore an animal that eats other animals

omnivore an animal that eats both plants and animals

decomposer an organism that gains nutrients by breaking down dead organisms into simpler nutrients There are many different organisms in an ecosystem that are interdependent on one another. That is, they each have a role in maintaining the survival of one another. While plants convert the energy from the Sun into new leaves and stems, the herbivores that eat the plants use this stored energy to move and grow. Carnivores such as dogs eat the herbivores as part of their meat diet. Most humans eat both meat and plants, making them omnivores.

Insects, birds and bats pollinate plants

Plants and animals interact in their search for food. Bees and other insects, as well as some birds and bats, transfer pollen from plant to plant. While stopping at a fl ower for a sip of nectar, the animals or insects get dusted with pollen.

Figure 1 Some plants use bats to transfer pollen from one plant to another. Figure 2 Insects, such as bees, are important pollinators of plants.

When the animals or insects fl y to another fl ower of the same or similar species, some of that pollen brushes off and the pollinated fl owers are then able to produce seeds. Pollination is important not only for wild plants but also for crop plants. More than 70 per cent of plant species worldwide, including fruits and vegetables, are pollinated by animals, insects or birds.

Some organisms decompose organic matter

Locked inside all organisms is an enormous amount of nutrients. All organisms in a food web end up passing these nutrients and energy on to decomposers . Decomposers – such as bacteria, fungi and invertebrates (slugs and worms) – get the food they need by feeding on dead things. This prevents the dead organisms from piling up. Instead, the nutrients stored in the dead organisms are used for energy by the decomposers. When another organism eats a decomposer, the nutrients once again become part of the food chain. The nutrients that pass through the decomposers as waste end up in the soil in simpler forms. Plant roots can then absorb the nutrients and the cycle starts again. Imagine what life would be like without decomposers!

Figure 3 Decomposers recycle important nutrients in an ecosystem.

Figure 4 Forested water catchment areas are vital for keeping Melbourne’s water supplies clean.

Wetlands and forests help clean water

If you poured dirty water through a filter, you would expect cleaner water to come out. A similar thing happens in nature when water passes through a forest or wetland ecosystem. By slowing the flow of water, the plants and bacteria trap some of the pollutants and sediments. But plants are not the only living things that clean water. Aquatic animals, such as freshwater clams, pump water through their bodies to filter out food for themselves and, in so doing, clean the water they live in.

8.2 Check your learning

Remember and understand

1 Identify the name used for animals that eat both meat and plants. 2 Describe one of the consequences that may occur if decomposers did not exist. 3 List three organisms that act as decomposers.

Apply and analyse

4 Describe how you could be affected if all bees died as a result of infection.

5 We get the energy we need by eating other living organisms. Identify the

Figure 5 Mushrooms (fungi) are decomposers. They get the nutrients they need by feeding on dead things, such as rotting logs.

source of energy for the following organisms. a producers b first-order consumers

c decomposers

Evaluate and create

6 Design an organism for a food web. Identify the role of your organism in a food web.

7 Describe the factors that could affect the survival of your organism in a bush environment.