Natural Selection · Paper 1 — Free Biology SL Practice Questions

In a grassland, meadow voles (Microtus pennsylvanicus) occupy patches of dark soil and patches of light soil. Hawks hunt voles by sight. Over 10 generations, the allele for dark fur increases in frequency on dark soil patches and the allele for light fur increases in frequency on light soil patches, while voles with intermediate fur colour decline in both patch types. Which type of natural selection is acting on fur colour in this population?

In a meadow, grasshoppers show heritable variation in body colour: green, yellow, and brown. A visually hunting bird species colonises the meadow. After three generations, the frequency of brown grasshoppers has increased significantly while the frequencies of green and yellow grasshoppers have both decreased. Which type of natural selection best describes this change in the grasshopper population?