Explain that plants are called ‘producers’ as they produce their own food. Use the term ‘autotrophs’ for producers.
Define: consumers or heterotrophs, primary consumer or herbivores, secondary consumer or carnivores and omnivores.
Construct and interpret food chains and food webs using Australian examples.
Identify producers, consumers and decomposers in a food chain or food web
The food chain describes who eats whom in the wild. Every living thing—from one-celled algae to giant blue whales—needs food to survive. Each food chain is a possible pathway that energy and nutrients can follow through the ecosystem.
For example, grass produces its own food from sunlight. A rabbit eats the grass. A fox eats the rabbit. When the fox dies, bacteria break down its body, returning it to the soil where it provides nutrients for plants like grass.
Of course, many different animals eat grass, and rabbits can eat other plants besides grass. Foxes, in turn, can eat many types of animals and plants. Each of these living things can be a part of multiple food chains. All of the interconnected and overlapping food chains in an ecosystem make up a food web.
A food web consists of all the food chains in a single ecosystem. Each living thing in an ecosystem is part of multiple food chains. Each food chain is one possible path that energy and nutrients may take as they move through the ecosystem. All of the interconnected and overlapping food chains in an ecosystem make up a food web.
Organisms in food webs are grouped into categories called trophic levels. Roughly speaking, these levels are divided into producers (first trophic level), consumers, and decomposers (last trophic level).
Producers
Producers make up the first trophic level. Producers, also known as autotrophs, make their own food and do not depend on any other organism for nutrition. Most autotrophs use a process called photosynthesis to create food (a nutrient called glucose) from sunlight, carbon dioxide, and water.
Plants are the most familiar type of autotroph, but there are many other kinds. Algae, whose larger forms are known as seaweed, are autotrophic. Phytoplankton, tiny organisms that live in the ocean, are also autotrophs. Some types of bacteria are autotrophs. For example, bacteria living in active volcanoes use sulfur, not carbon dioxide, to produce their own food. This process is called chemosynthesis.
Consumers
The next trophic levels are made up of animals that eat producers. These organisms are called consumers.
Consumers can be carnivores (animals that eat other animals) or omnivores (animals that eat both plants and animals). Omnivores, like people, consume many types of foods. People eat plants, such as vegetables and fruits. We also eat animals and animal products, such as meat, milk, and eggs. We eat fungi, such as mushrooms. We also eat algae, in edible seaweeds like nori (used to wrap sushi rolls) and sea lettuce (used in salads). Bears are omnivores, too. They eat berries and mushrooms, as well as animals such as salmon and deer.
Primary consumers are herbivores. Herbivores eat plants, algae, and other producers. They are at the second trophic level. In a grassland ecosystem, deer, mice, and even elephants are herbivores. They eat grasses, shrubs, and trees. In a desert ecosystem, a mouse that eats seeds and fruits is a primary consumer.
In an ocean ecosystem, many types of fish and turtles are herbivores that eat algae and seagrass. In kelp forests, seaweeds known as giant kelp provide shelter and food for an entire ecosystem. Sea urchins are powerful primary consumers in kelp forests. These small herbivores eat dozens of kilograms (pounds) of giant kelp every day.
Secondary consumers eat herbivores. They are at the third trophic level. In a desert ecosystem, a secondary consumer may be a snake that eats a mouse. In the kelp forest, sea otters are secondary consumers that hunt sea urchins.
Tertiary consumers eat the secondary consumers. They are at the fourth trophic level. In the desert ecosystem, an owl or eagle may prey on a snake.
There may be more levels of consumers before a chain finally reaches its top predator. Top predators, also called apex predators, eat other consumers. They may be at the fourth or fifth trophic level. They have no natural enemies except humans. Lions are apex predators in the grassland ecosystem. In the ocean, fish like the great white shark are apex predators. In the desert, bobcats and mountain lions are top predators.
Detritivores and decomposers make up the last part of food chains.
Detritivores are organisms that eat nonliving plant and animal remains. For example, scavengers such as vultures eat dead animals. Dung beetles eat animal feces.
Decomposers, like fungi and bacteria, complete the food chain. Decomposers turn organic wastes, such as decaying plants, into inorganic materials, such as nutrient-rich soil. They complete the cycle of life, returning nutrients to the soil or oceans for use by autotrophs. This starts a whole new series of food chains.
Food webs are defined by their biomass. Biomass is the energy in living organisms. Autotrophs, the producers in a food web, convert the sun's energy into biomass. Biomass decreases with each trophic level. There is always more biomass in lower trophic levels than in higher ones.
Because biomass decreases with each trophic level, there are always more autotrophs than herbivores in a healthy food web. There are more herbivores than carnivores. An ecosystem cannot support a large number of omnivores without supporting an even larger number of herbivores, and an even larger number of autotrophs.
A healthy food web has an abundance of autotrophs, many herbivores, and relatively few carnivores and omnivores. This balance helps the ecosystem maintain and recycle biomass.
Every link in a food web is connected to at least two others. The biomass of an ecosystem depends on how balanced and connected its food web is. When one link in the food web is threatened, some or all of the links are weakened or stressed. The ecosystems biomass declines.
The loss of plant life usually leads to a decline in the herbivore population, for instance. Plant life can decline due to drought, disease, or human activity. Forests are cut down to provide lumber for construction. Grasslands are paved over for shopping malls or parking lots.
The loss of biomass on the second or third trophic level can also put a food web out of balance. Consider what may happen if a salmon run is diverted. A salmon run is a river where salmon swim. Salmon runs can be diverted by landslides and earthquakes, as well as the construction of dams and levees.
Biomass is lost as salmon are cut out of the rivers. Unable to eat salmon, omnivores like bears are forced to rely more heavily on other food sources, such as ants. The area's ant population shrinks. Ants are usually scavengers and detritivores, so fewer nutrients are broken down in the soil. The soil is unable to support as many autotrophs, so biomass is lost. Salmon themselves are predators of insect larvae and smaller fish. Without salmon to keep their population in check, aquatic insects may devastate local plant communities. Fewer plants survive, and biomass is lost.
A loss of organisms on higher trophic levels, such as carnivores, can also disrupt a food chain. In kelp forests, sea urchins are the primary consumer of kelp. Sea otters prey on urchins. If the sea otter population shrinks due to disease or hunting, urchins devastate the kelp forest. Lacking a community of producers, biomass plummets. The entire kelp forest disappears. Such areas are called urchin barrens.
Human activity can reduce the number of predators. In 1986, officials in Venezuela dammed the Caroni River, creating an enormous lake about twice the size of Rhode Island. Hundreds of hilltops turned into islands in this lake. With their habitats reduced to tiny islands, many terrestrial predators weren’t able to find enough food. As a result, prey animals like howler monkeys, leaf-cutter ants, and iguanas flourished. The ants became so numerous that they destroyed the rainforest, killing all the trees and other plants. The food web surrounding the Caroni River was destroyed.
https://www.montereybayaquarium.org/education/classroom-resources/games-and-activities/kelp-forests
What is used to indicate the flow of energy in a food chain or web
What happens to energy as we move from step to step in a chain or web?
Define food web.
What is meant by trophic levels?
Define autotroph.
The 1st trophic level consists of _______________ consumers called _________________.
Name the 2nd trophic level (both names).
Secondary consumers may be _______________ eating meat or _______________ that eat both plants and animals.
What is the 3rd trophic level called?
What is the 4th trophic level called?
At the 5th trophic level would be _____________ consumers that eat _____________ consumers.
Give an example of 3 detrivores. On what do they feed?
What organism feeds on dead plants and animals and helps recycle them? _____________________
Both ______________ and ______________act as decomposers
Can an organism fill more than one trophic level --- yes or no? Give an example.
From this food web on the left:
1. Show two food chains (do not include the plant litter, dead animals, bacteria or fungi).
2 a. Which population/ trophic level has the largest biomass?
b. Which has the smallest biomass?
3. Draw a food pyramid using the organisms from one of your food chains.
4. Name one:
a. second-order consumer:
b. fourth-order consumer:
5. Name two herbivores.
6. Name an omnivore.
7. Name one predator.
8. Name two prey eaten by the eagle.
9. Name three consumers that are in competition for the grass.
10. Identify the two types of decomposer organisms.
11. Describe the role of the decomposers.
12. What would happen in this food web if:
a. the number of rabbits increased?
b. the wedge-tailed eagle became extinct?