The diagram shows the impact of birds feeding on a population of beetles over time - HSC - SSCE Biology - Question 3 - 2019 - Paper 1

To determine what accounts for the change in the beetle population as depicted in the diagram, we must analyze the influence of the birds on the beetles over time. The presence of birds as predators exerts a selective pressure on the beetle population. This implies that the traits of the beetles that make them more resistant to predation will be favored through natural selection.

The correct choice among the given options is D. Environmental pressure. The birds represent an environmental factor that affects the survival of the beetles, suggesting that environmental changes, in this case, predation, lead to shifts in the beetle population over time.