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Just recently, a parent on our Parent Support Group asked for help with a question on the topic of Web of Life, also known as Interactions.

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As such, in today’s article, I’ll be sharing how to tackle questions on the graphical representations of a food chain using the method of elimination to help us arrive at the correct answer.

Question

Screen Shot 2018-08-01 at 7.56.25 PM

Given that

What happens to the population of the other organisms if Organism Y is removed from the food chain?

 

Thought Process

#1 Look At The Starting Base

One rule of thumb is that an organism lower in the food chain has a larger population.

Hence, as indicated in red on the y-axis, the population of R would be the largest as it is the food producer, followed by W, then X and lastly Z, the king/predator.

Using this train of thought, we can safely eliminate Option 3 as its starting base is incorrect.

#2 Look At The Effect of Removing Organism Y From The Food Chain

In this case, we examine the effect by looking at the relationship between the prey and the predator.

How does the effect of increasing/decreasing a population affect its prey or predator?

Option 1

Since Organism Z is the predator of Organism Y, removing Organism Y from the food chain will cause the population of Organism Z to decrease as its only food source (Organism Y) is absent.

Option 2

Since Organism X is the prey of Organism Y, removing Organism Y will cause the population of Organism X to increase as there are no predators feeding on Organism X.

Option 3

Since Organism W is the prey of Organism X, an increase in population of Organism X will cause the population of Organism W to decrease as there are more Organism X to feed on Organism W.

Option 4

Lastly, since Organism W feeds on Organism R, a decrease in population of Organism W will cause the population of Organism R to increase as there are lesser Organism W to feed on Organism R.

In conclusion, we can see that removing Organism Y from the food chain will cause the population of Organism R and Organism X to increase and the population of Organism W and Organism Z to decrease.

Answer

Therefore, the answer to this question is Option 2.

I hope that this article has helped to explain how to apply the elimination method when tackling such questions that use graphical representations of food chains!