Question

Assignment: Part IIIUse the graph and the information provided to answer the questions.Stickleback fish protect themselves from predators with a thick covering of brownish plates. They feed onsmall aquatic organisms and are preyed upon by bigger fish like trout. In a certain lake, the number ofstickleback fish was documented over a period of 30 years. During this time, the clarity of the lake wateralso changed.1. How did the occurrences of the different traits change over the 30-year period? Use evidence fromthe graph to support your answer. Using what you know about natural selection and adaptation, whatgeneralization can you make based on these changes? (15 points)

Answer 1

We have that the Stickleback fish were documented over those 30 years, and along that time, the clarity of the lake's water they were studied was changing over the years.

We have that these species feed upon smaller aquatic organisms, and they're preyed on by biggest fishes, as trouts.

Stickleback, to avoid this, developed a particular structure in their bodies, known as the brownish plates, which over the years began to cover their half body, to cover the whole body.

We have then the following:

1. Clearer water:

Plates covering only half of their body

2. Darker water:

Plates covering almost the whole of their body

To what could we attribute that change in their morphology?

Since the water began to be more obscure than the former, the parts of the body of the fish that were shiny, like the ones not covered by brownish plates, were easier to see for their predators. So the reason these fishes could have developed a whole brownish plate structure could have been the need to be less visible to those trout.

So the occurrences of the different traits changed over the 30-year period because of the pressure that represented the presence of the trout which feed on the stickleback fishes, and also due to the increase in turbidity (water getting less clear) of the water.