i am sure this question would be in ur text book.
anyway, i would go this route to answering the question.
Talk about the variation of species in the population. if environmental effects such as the climate or destruction of habitats occured, those more suited to the newly modified environment would survive and the ones not suited would not survive. make sure you give examples - it could be the variance of a specie of fauna that exists in two contrasting climates or the evolution of a particular specie of animal that survives in two contrasting environments.
you could also talk about the effect of say a bush fire in the forest affecting the reproduction of plants. eg, certain plants in the forest need extreme heat, such as that from bushfires to release its seeds. the effect of this environment change is therefore the promotion of new plant growths.
please make sure with ur teacher that this is the answer that the question expects.
