Introduction
The ecosystem is an assorted web of food chains. Which species eats another species? Which species gets eaten? Today, we will take a look at a complicated food web and determine which of the species are predators only, preys only, and both predator and prey.
We will be analysing a question on the topic of the Web of Life from the 2017 Singapore Hokkien Huay Kuan (SHHK) P6 SA2 Examination Paper.
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Let’s Take A Look At This Question
Source: Singapore Hokkien Huay Kuan – 2017 P6 SA2 Examination Paper [Q35]
Thought Process
We have a food web shown above. Before we even try to identify the ‘Predator only’, the ‘Prey only’, and the ‘Predator and prey’, what I always advise my students to do is to first annotate who the ‘Food producer’ is and who the ‘King’ is.
🌱 Who Is The Food Producer? 🌱
A “food producer” is a plant, and a plant is an organism that makes its own food. Therefore, it does not consume any organisms.
As such, how should the arrows look like for a food producer?
📍 Identifying The Food Producer📍
⤴️ Food producers should only have arrows pointing away from them, not towards them at all.
Who’s the food producer here? It is R.
As you can see, there are only arrows pointing away from it, no arrows pointing towards it. Therefore, we can conclude that R is the food producer. It’s the plant.
Are there any other food producers in the food web? All the other organisms have arrows pointing towards them, so they cannot be food producers.
Next, let’s identify the ‘king’. What is a ‘king’?
👑 Who Is The King? 👑
A “king” is an animal that does not get eaten up by any other animals at all.
Can I have arrows pointing away from a king?
What does this mean? That means the king is getting eaten up by another organism. This is not possible. Otherwise, it’s not a king.
Therefore, there should only be arrows pointing towards a king and nothing away from it.
Let’s look at the food web above and figure out who this king is.
It is S, the one with arrows pointing only towards it and nothing away from it. S is the king.
Is S the only king? U is also another organism that has no arrows pointing away from it. U is also the king.
Predator Only
If you look at our options, we’re supposed to figure out who’s the ‘Predator only’, which means it is not a prey. If it is not a prey, it doesn’t get eaten up by any other animals as well. Isn’t that the king? Yes.
So, a ‘Predator only’ is the king. We have already figured out who the kings are. They are S and U. Let’s go and choose S and U under ‘Predator only’, which are options (2) and (3).
Prey Only
Next, what’s a ‘Prey only’? A ‘Prey only’ means that it is not a predator. If it is not a predator, it doesn’t eat any other animal. What does it eat then? It only feeds on plants.
🌿 Who Are Preys Only? 🌿
‘Preys only’ are “herbivores.” These are animals that eat only plants. They don’t eat any animals.
Hence, to find the ‘Prey only’, the trick is to identify the herbivores.
Let’s identify all the herbivores. Herbivores are animals that feed on food producers, so they have to be feeding on R.
Is T a herbivore? Yes. It’s only feeding on a plant, R.
Is P a herbivore? Yes. P is only eating on the food producer, R.
Is Q a herbivore? Yes. Q is feeding only on R.
Is V a herbivore? V is indeed feeding on R. However, is it considered a herbivore? No. Because it is also feeding on another animal.
That means V is an omnivore.
📍 Who Are Omnivores?📍
“Omnivores” are animals that feed on both plants and animals ↕️
How about W? Is W feeding on R? No. Since it doesn’t feed on a plant at all, you can conclude that W is a carnivore.
📍Who Are Carnivores?📍
“Carnivores“ are animals that feed on meat only (like animals). They don’t feed on plants at all 🍖
How about U? Does U feed on R? No. We can conclude that U is a carnivore.
How about S? Does S feed on R? No, so S is a carnivore.
We have then figured out who the herbivores are, or the ‘Preys only’. They are P, Q, and T, which is option (2).
Source: Singapore Hokkien Huay Kuan – 2017 P6 SA2 Examination Paper [Q35]
Predator and Prey
Next, we have to figure out which animals are both a ‘Predator and prey’. If it is a predator and prey, it gets eaten up by another animal, meaning it’s a prey. At the same time, it also feeds on another animal, so it is considered to be a predator.
If it feeds on only plants, can it be considered a predator? No, because in order to be considered a predator, you need to be feeding on an animal.
Which groups are definitely not a prey and a predator at the same time? Herbivores are definitely not a predator. If it’s not a predator, it cannot be considered a ‘Predator and a prey’. Hence, we have to exclude all the herbivores. Which other organisms can we exclude?
Can a food producer be a predator and a prey? No, a food producer is not a predator. It is not a prey in the first place. We can then exclude them.
There’s one more group that we can exclude. It is an organism that’s a ‘Predator only’ because if it’s a ‘Predator only’, it is definitely not a prey. Who’s that? The kings.
Basically, a ‘Predator and a prey’ is everything except herbivores, food producers, and kings. Which are these organisms?
Can we count S and U? No, S and U are the kings.
Can we count T? No, T is a herbivore.
Can we count R? No, R is the food producer.
Can we count P and Q? No, because P and Q are herbivores.
So, we are left with V and W.
Suggested Answer
Option (2).
Conclusion
Looking at a food web can be daunting. The possibilities may seem endless!
But following our discussion, I hope you are able to understand the thought processes in analysing a food web and determining its food producers, herbivores, carnivores and omnivores.
The best thing about these tips is that they can also be applied to other Web of Life questions that involve food webs!
Check out our other articles on the Web of Life and continue to keep a lookout for more articles! 🙂
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