Figures
Figure 1

Daphnia water fleas change their behavior if fish are present.
Left: During the day Daphnia migrate to deeper, darker regions of the lake if they detect chemical signals called kairomones (not shown) that are released by fish. Middle: At night, when fish cannot see them, Daphnia move up to the water near the surface to eat the microalgae (green circles) that are plentiful there. Right: When no fish are present, there are no kairomones to detect, and Daphnia stay near the surface day and night.
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