The Energy Flow: Food Chains and Food Webs
The Energy Flow: Food Chains and Food Webs
At the end of this lesson, you are expected to:
Explain that food webs are more realistic representations of energy flow than food chains.
Identify multiple feeding relationships within a given food web.
Describe how changes in one population can affect other populations in a food web.
Appreciate the interconnectedness of life in an ecosystem.
Imagine you are a detective trying to figure out who eats whom in a simple forest. I'll give you a list of animals and plants. Your job is to connect them with arrows to show who eats whom, creating a food chain.
Here are your clues:
Grass: Grows in the sun.
Grasshopper: Loves to munch on grass.
Frog: Enjoys a tasty grasshopper.
Snake: Thinks frogs are delicious.
Eagle: A powerful bird that can catch a snake.
Now, draw lines with arrows showing the flow of energy. Remember, the arrow points from the organism being eaten to the organism that eats it! For example, if a grasshopper eats grass, you draw an arrow from Grass to Grasshopper.
Take your time and think about the energy flow. What happens after the grasshopper eats the grass? What happens after the frog eats the grasshopper?
Once you've drawn your food chain, think about this: Is this the only way these animals get their food? Could the frog eat anything else? Could the snake be eaten by anything else? We'll explore these questions in our lesson today!
Hello, young scientists! Last time, we learned about food chains. Remember how they show a simple, straight line of who eats whom? Like our forest example: Grass → Grasshopper → Frog → Snake → Eagle. This shows how energy moves from one living thing to another. The grass gets energy from the sun, the grasshopper gets energy from the grass, the frog gets energy from the grasshopper, and so on.
But think about our frog. Does a frog only eat grasshoppers? If you've ever seen a frog, you know they are quite the hunters! They might also eat other insects, like flies or beetles. And what about the snake? While eagles might eat snakes, could a bigger animal, like a wild pig or a monitor lizard, also eat a snake?
The truth is, nature is much more complicated and exciting than a single food chain! Most animals have more than one food source, and they can also be food for more than one type of predator. This is where our new topic comes in: Food Webs!
What is a Food Web?
A food web is like a collection of many interconnected food chains. Instead of a single line, it looks more like a messy, tangled web, showing all the different feeding relationships in an ecosystem. It's a more realistic picture of how energy flows in nature because it shows that most organisms have multiple options for food and multiple predators.
Why are Food Webs More Realistic?
Imagine you are a rabbit. Your main food is grass, right? So, Grass → Rabbit. But what if there's a drought, and the grass isn't growing well? If you are a rabbit, you might start looking for other plants to eat, like clover or certain leaves. So, now we have Grass → Rabbit and Clover → Rabbit.
Now, who eats rabbits? Foxes are famous for eating rabbits. So, Rabbit → Fox. But what if there are also wolves in the area? Then we have Rabbit → Fox and Rabbit → Wolf.
See how quickly it gets more complex than a simple chain? A food web shows all these connections.
Let's Look at a Philippine Example: A Forest Food Web
The Philippines is home to amazing forests with incredible biodiversity! Let's imagine a simplified food web from a Philippine forest.
Producers: These are the plants that make their own food using sunlight. In our forest, we have:
Trees and their leaves: (like Mahogany, Narra)
Grasses: (various types)
Fruits: (like Mango, Lanzones)
Nectar: (from flowers)
Primary Consumers (Herbivores): These animals eat the producers.
Insects: (like butterflies, beetles, grasshoppers) that eat leaves, fruits, or nectar.
Fruit Bats: that eat fruits.
Deer: that eat leaves and grasses.
Wild Pigs (Baboy Ramo): that eat fruits, roots, and sometimes insects.
Secondary Consumers (Carnivores or Omnivores): These animals eat the primary consumers.
Frogs: that eat insects.
Lizards: that eat insects.
Birds: (like the Philippine Tarsier, which eats insects and small vertebrates, or the Palawan Peacock-Pheasant, which eats seeds and insects)
Snakes: that eat frogs and lizards.
Monkeys: (like the Philippine Long-tailed Macaque) that are omnivores, eating fruits, leaves, insects, and small animals.
Tertiary Consumers (Carnivores): These animals eat the secondary consumers.
Snakes: that eat frogs.
Birds of Prey: (like the Philippine Eagle) that eat snakes, monkeys, and other animals.
Wild Cats: (like the Asian Golden Cat) that might eat monkeys or wild pigs.
Decomposers: These are crucial! They break down dead plants and animals, returning nutrients to the soil.
Fungi: (Mushrooms)
Bacteria
Putting it Together: The Forest Food Web
Now, let's try to draw some connections. Remember, arrows show the direction of energy flow.
Grasses → Grasshoppers → Frogs → Snakes → Eagles (This is one food chain!)
Grasses → Deer → Wild Cats
Leaves → Insects → Birds → Snakes → Eagles
Fruits → Fruit Bats → Eagles
Fruits → Monkeys → Wild Cats
Insects → Monkeys → Wild Cats
Frogs → Monkeys (Monkeys might eat frogs too!)
Snakes → Monkeys (Some monkeys might eat snakes, or snakes might eat young monkeys!)
Dead Trees/Leaves/Animals → Fungi/Bacteria (Decomposers)
If we were to draw all these connections, it would look like a complex web!
Key Concepts in Food Webs:
Producers: The base of the food web. They create their own food. Think of them as the "energy makers."
Consumers: Organisms that get energy by eating other organisms.
Primary Consumers (Herbivores): Eat producers.
Secondary Consumers (Carnivores/Omnivores): Eat primary consumers.
Tertiary Consumers (Carnivores): Eat secondary consumers.
Quaternary Consumers (Apex Predators): At the very top, eating tertiary consumers.
Decomposers: Nature's recyclers. They break down dead organic matter. Without them, dead things would pile up!
The 10% Rule in Food Webs:
Just like in food chains, energy transfer in food webs follows the 10% Rule. When an organism eats another, only about 10% of the energy from the food it ate is stored in its own body. The rest is used for its life processes (moving, growing, staying warm) or lost as heat.
This means that the higher up you go in a food web (towards the tertiary or quaternary consumers), the less energy is available. This is why there are usually fewer top predators than herbivores.
Interconnectedness and Impact of Change:
Food webs highlight how everything is connected. If one part of the web is affected, it can ripple through the entire ecosystem.
What happens if the insect population decreases drastically?
Frogs and lizards that eat insects will have less food. Their populations might shrink.
Birds that eat insects will also struggle to find food.
Monkeys that eat insects might have to rely more on fruits, potentially affecting fruit-bearing trees.
If the frog population shrinks, snakes that eat frogs will have less food, and so on up the chain.
What happens if a new predator is introduced that eats snakes?
The snake population might decrease.
This could lead to an increase in the frog population (since fewer frogs are being eaten by snakes).
An increase in frogs could lead to a decrease in the insect population (since more insects are being eaten by frogs).
This shows that ecosystems are delicate balancing acts. Every organism plays a role.
Let's Consider a Coral Reef Food Web (Another Philippine Example!)
The Philippines is also famous for its beautiful coral reefs, which have their own amazing food webs!
Producers:
Algae and Phytoplankton: Tiny plants and plant-like organisms that form the base.
Primary Consumers (Herbivores/Planktonivores):
Zooplankton: Tiny animals that eat phytoplankton.
Small Fish: (like Damsel fish) that eat algae.
Sea Urchins: that eat algae.
Turtles: that eat seagrass and algae.
Secondary Consumers:
Small Fish: (like Butterflyfish) that eat coral polyps or small invertebrates.
Crabs and Shrimp: that eat smaller organisms.
Jellyfish: that eat zooplankton and small fish.
Larger Fish: (like Groupers) that eat smaller fish.
Tertiary Consumers:
Sharks: that eat larger fish.
Dolphins: that eat fish.
Sea Eagles: that might eat fish or sea snakes.
Decomposers:
Bacteria
Connections in the Reef:
Phytoplankton → Zooplankton → Small Fish → Larger Fish → Sharks
Algae → Sea Urchins → Sea Stars (which eat sea urchins) → Larger Fish
Coral Polyps → Butterflyfish → Larger Fish → Sharks
Seagrass → Turtles → Sharks (though sharks are more likely to eat other fish)
Again, if the population of small fish decreases, the larger fish that eat them will have less food, and the sharks that eat the larger fish will also be affected. If pollution harms the algae and phytoplankton, the entire reef ecosystem suffers because the base of the food web is weakened.
Why is Understanding Food Webs Important?
Understanding food webs helps us see how important every living thing is. It teaches us about:
Ecosystem Balance: How different populations keep each other in check.
Energy Flow: How energy moves through an ecosystem.
Interdependence: How organisms rely on each other for survival.
Conservation: Why protecting habitats and biodiversity is crucial. If we lose one species, it can have a domino effect on many others.
Think about our role as humans. We are also part of food webs! We eat plants and animals, and we can also be prey for some animals (though less common in modern times). Our actions, like fishing or farming, can significantly impact food webs. Making sustainable choices helps maintain the health of these natural systems.
So, remember, nature isn't just one straight path; it's a beautiful, complex, and interconnected web of life!
4.a Guided Practice: Building a Mini Food Web
Let's practice identifying relationships in a food web. Imagine this simple ecosystem:
Organisms: Sun, Grass, Rabbit, Fox, Hawk, Berries, Deer, Wolf
Now, let's connect them!
Producers: Which of these make their own food using sunlight? (Hint: They are plants!)
Primary Consumers: Which organisms eat the producers?
_________________________ (eats Grass)
_________________________ (eats Grass and Berries)
Secondary Consumers: Which organisms eat the primary consumers?
_________________________ (eats Rabbit)
_________________________ (eats Rabbit and Deer)
_________________________ (eats Grasshoppers, if we added them, but let's stick to the list for now. Hawks often eat small rodents like rabbits.)
Tertiary Consumers: Which organisms eat the secondary consumers?
_________________________ (eats Fox)
Now, try to draw arrows to show the flow of energy. Remember, the arrow points from the one being eaten to the one that eats it.
Sun → Grass → Rabbit → Fox → Wolf
Sun → Grass → Deer → Wolf
Sun → Berries → Rabbit → Hawk
Sun → Berries → Deer → Fox
Can you see how the Rabbit is eaten by both the Fox and the Hawk? Can you see how the Deer is eaten by both the Fox and the Wolf? This is what makes it a web!
Interactive Activity: Food Web Charades!
Let's play a game! I'll write down different organisms from a food web on separate slips of paper. You will pick one slip and act out that organism and its role in the food web without speaking.
If you are a Producer: Act like you are soaking up the sun and growing! (e.g., swaying like a plant).
If you are a Primary Consumer: Act like you are happily munching on plants. (e.g., pretend to eat leaves).
If you are a Secondary Consumer: Act like you are hunting and eating a primary consumer. (e.g., pretend to catch and eat a "plant-eater").
If you are a Tertiary Consumer: Act like you are hunting and eating a secondary consumer.
The rest of the class will guess which organism you are and what your role is (producer, primary consumer, etc.). Then, we can try to connect ourselves with imaginary arrows to build a human food web!
Independent Practice: My Own Food Web
Choose one of the following ecosystems:
A Philippine Beach/Mangrove Area
A Rice Field
Research (or imagine, if research is not possible) at least 5 organisms that live in that ecosystem. Include producers, primary consumers, secondary consumers, and maybe a tertiary consumer or decomposer.
Draw your own food web, showing the feeding relationships with arrows. Label each organism with its role (Producer, Primary Consumer, Secondary Consumer, Tertiary Consumer, Decomposer).
Write a short paragraph explaining one interesting connection in your food web and what might happen if one of the organisms disappeared.
Think about the farmers in the Philippines who grow rice. They want healthy crops, right? But sometimes, pests like rice stem borers (insects) can damage the rice plants.
Rice Plants (Producers) → Rice Stem Borers (Primary Consumers)
What eats the rice stem borers? Birds like egrets or kingfishers (Secondary Consumers) often eat these insects.
Rice Stem Borers → Egrets/Kingfishers
What happens if farmers use too many pesticides that kill all the insects, not just the pests?
The rice stem borers might decrease, which seems good.
But the egrets and kingfishers that rely on these insects for food will also suffer. They might leave the area or starve.
If the insect-eating birds disappear, other insects (maybe even ones that eat the pests!) might increase because they have fewer predators.
This shows how even in a simple farm ecosystem, everything is connected. Protecting biodiversity, even the "small" creatures like insects and birds, helps maintain a natural balance that can benefit farming in the long run. It's a reminder that our actions have consequences for the entire food web.
A food web shows many interconnected food chains in an ecosystem.
It is a more realistic way to show how energy flows because most animals eat more than one thing and are eaten by more than one thing.
The main parts of a food web are Producers, Consumers (Primary, Secondary, Tertiary), and Decomposers.
Energy transfer in food webs generally follows the 10% rule.
Changes in one part of a food web can affect many other parts, showing the interdependence of all living things.
Observe Your Surroundings: Look around your home, schoolyard, or a nearby park. Can you identify any producers (plants)? Can you see any insects or birds that might be consumers? Try to imagine the simple food chains or food webs that exist right there!
Be a Responsible Consumer: Think about the food you eat. Where does it come from? How does it fit into a larger food web? Making choices that support sustainable farming and fishing helps protect ecosystems and their food webs.
Protect Habitats: Understand that protecting natural areas like forests and coral reefs is crucial because they are home to complex food webs. Even small actions like not littering can help keep these environments healthy for all the organisms living there.
Share Your Knowledge: Tell your family and friends about food webs and why they are important! You can even draw a simple food web of a local park or your backyard to share with them.
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