Evolution and Speciation · Paper 2 — Free Biology SL Practice Questions

A population of a small mammal species lives on an island with two distinct habitats: a dark, forested area and a light, sandy beach. The mammals are preyed upon by birds that hunt by sight. A biologist recorded fur colour frequencies over several generations. Generation 1 — $45\%$ light fur, $55\%$ dark fur — $60\%$ light fur, $40\%$ dark fur Generation 10 — $82\%$ light fur, $18\%$ dark fur — $21\%$ light fur, $79\%$ dark fur - Average offspring per breeding pair, Generation 1: $4.2$ - Average offspring per breeding pair, Generation 10: $3.8$

A farmer notices that a species of weed in his fields has become increasingly resistant to a common herbicide over a period of 8 years. In Year 1, the herbicide at the recommended dose killed $95\%$ of the weed population. By Year 8, the same dose killed only $15\%$ of the weed population. The farmer also observed that individual weed plants exposed to sub-lethal doses of the herbicide sometimes produced offspring that were slightly more resistant, even without direct herbicide exposure to those offspring.

A population of Poecilia reticulata (guppies) lives in a stream in Trinidad. One section of the stream contains the predator fish Crenicichla alta; an adjacent upstream section, separated by a waterfall, is predator-free. The waterfall prevents gene flow between the two populations. Guppies in the predator-present section mature at a smaller size and produce more, smaller offspring than those in the predator-absent section. A researcher recorded the following data over one generation: Section — Average offspring per female — Survival rate to reproductive age Predator-present — 20 — $10\%$ Predator-absent — 8 — $60\%$