Biology 9700 · AS & A Level · Natural and artificial selection
Natural and artificial selection — practice question
A $28$-year investigation of Magellanic penguins, Spheniscus magellanicus, in Argentina supplies evidence for natural selection. Magellanic penguins lay eggs in nests. They use their bills (beaks) to seize prey and to feed their chicks (offspring) in the nest. Each breeding pair returns to the same nest every year. Bill size data were gathered annually from 1983 to 2010. Bill size was worked out from bill length and bill depth. There was variation in bill size among individuals. In 1983, all penguins in one area were tagged. Each year, all tagged penguins were measured, and their new chicks were tagged and measured too. For every year in the study, food availability was estimated. A statistical analysis was then carried out to determine whether selection had occurred.
(a)[2]
Explain why bill size is an example of continuous variation.
(b(i))[1]
Statistical testing of the data indicated that selection was not significant in most years of the study. Even so, bill size rose significantly in four years. Name the type of selection that took place in those four years.
(b(ii))[2]
In those same four years, food availability was low. Explain how the bill-size and food-availability data support the idea of the 'struggle for existence' in natural selection.
(c)[1]
Further study found that, in some years, larger bill sizes in adult males were associated with higher reproductive success. Reproductive success was recorded as the number of chicks that survived per adult each year. Suggest why larger bill size in adult males was linked to higher reproductive success.
Worked solution & mark scheme
This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Neither discrete nor categorical” …