Video Transcript
The diagram shows a simple aquatic
food chain. Based on this diagram, what is
likely to happen to the killer whales if the sea lions go extinct? (A) Their population will
increase. (B) Their population will
decrease. Or (C) there will be no change in
the killer whale population.
This question asks us about the
effect of extinction on a food chain, so let’s start by reviewing these two
terms.
A food chain is a diagram that
represents the transfer of energy, in the form of food, from one organism to
another. In this food chain, algae make
their own food by using sunlight to perform photosynthesis. You may have learned that organisms
that can make their own food using light or chemical energy are called
producers. The first level of a food chain
always consists of producers. The other levels are consumers, who
must eat other organisms for energy. So, in the aquatic food chain here,
algae provide energy to the fish that eat them, fish provide energy to sea lions,
and sea lions provide energy to killer whales.
A species is extinct when all
individuals have died out. Let’s remove sea lions from the
food chain to represent their extinction. We can see that killer whales can
no longer rely on sea lions as an energy source. Some whales may be able to find
alternative food sources. Even so, without sea lions, there
will be less total energy available for the killer whale population.
The decrease in available energy
due to sea lion extinction is likely to affect the killer whale population in
several ways. Some whales may die from
starvation. Others may die from disease,
because without enough food, they become too weak to fight off infections. Female killer whales that do
survive are likely to reproduce less frequently than before the sea lion
extinction. This is because reproduction takes
a lot of energy, particularly for killer whales, who watch over their calves
constantly and nurse them for up to two years. In fact, scientists have found that
females increase their food intake by around 40 percent when nursing. So it makes sense that when less
food is available, fewer calves will be born or survive to maturity.
We can see that the effects of sea
lion extinction are likely to cause the killer whale population to decrease. Therefore, the correct answer is
option (B): their population will decrease.
