Explain how mass extinction events can lead to increased rates of speciation in surviving lineages.

IB DP Biology Standard Level (2023 syllabus) — D4.2 Stability and change · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Mass extinction events remove many species, leaving ecological niches empty and reducing competition for resources.

Surviving lineages can then expand into these vacated niches, often undergoing adaptive radiation.

Fragmentation of habitats during the extinction can isolate populations, promoting allopatric speciation.

Different selection pressures in the new or altered environments drive divergence, eventually producing reproductive isolation and new species.

Examiner tips

Use the word "eliminate" or "remove" for mass extinction; mention "ecological niches". Show the link between reduced competition and adaptive radiation. Include allopatric speciation as a mechanism. Explain how divergent selection leads to reproductive isolation.

Common mistakes

Confusing extinction with speciation; not linking reduced competition to adaptive radiation. Forgetting to mention geographic isolation. Using vague terms like "change" instead of specific selection pressures.

Mark scheme (4 marks)

Mass extinction events eliminate large numbers of species, reducing competition for resources / ecological niches
Surviving lineages can expand into newly vacated niches / undergo adaptive radiation
Populations of survivors may become geographically isolated in fragmented habitats, leading to allopatric speciation
Different selection pressures in different niches/environments drive divergence, eventually producing reproductive isolation and new species

Key terms in this question

mass extinction