Area Pale beetles / % Dark beetles / % Sandy soil 82 18 Volcanic soil 15 85 Fig. 3.1 A species of ground beetle lives in two nearby areas: one has pale, san...

This question tests natural selection through camouflage in ground beetles. Birds hunt by sight, so beetles that match their background survive better.

(a) The process producing the difference is natural selection [1].

(b) Explain why dark beetles dominate the volcanic soil: on dark soil, dark beetles are better camouflaged / harder for birds to see [1]; pale beetles are more visible and are eaten more [1]; so dark beetles are more likely to survive and reproduce [1]; and they pass on the allele for dark colour to their offspring, so dark beetles increase in number [1] [4]. Survival advantage plus inheritance is the full chain.

(c) The variation in colour originally comes from (random) mutation [1].

(d) A new advantageous variation spreads because: a mutation produces the new variation in one beetle [1]; the beetle with the advantage is more likely to survive and reproduce [1]; it passes the allele on to its offspring [1]; and over many generations the proportion of beetles with the advantageous feature increases [1] [4].

(e) If all birds were removed: the selection pressure removing pale beetles is gone [1]; so the proportion of pale beetles may increase / the difference between the two areas may reduce [1] [2]. Without predation there is no advantage to being camouflaged.

(f) Any one abiotic selection pressure: temperature, humidity / water availability, or light intensity [1].