1) In the above picture you can see a small streamlet running downhill. On its way down to the pond it takes multiple steps, producing small puddles. The picture is only to give you an idea, imagine there are a lot more of these puddles. Down in the pond there are two fish species very similar in appearance, but one of them reproduces sexually – each individual needing a mate of the opposite sex – while the other can reproduce without mating (in other words it reproduces asexually). Looking closer at these two species, you realize that one of them has far more infections, parasites, and fungi than the other.

Which one and why?

2) Every now and then, some of the fish manage to jump up the hill into the next puddle. As the years go by, they may finally reach the small pond on the top of the hill. Assume that these animals can reproduce rather quickly and that only a few of the fish manage to jump up. Looking at the fish in the uppermost pond, you notice both species have similar amounts of infections, parasites, and fungi.

Why is this?

3) What could you do to change the number of infections and etc. found in both species back to the distribution seen in the pond at the very bottom?

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