The evolution of species

Explain what a species is according to the biological species concept (interbreeding to produce fertile offspring) and give an example of two closely related animals belonging to different species.

Look at the diagram, which shows three stages in the evolution of a population divided by a geographical barrier. What is speciation? Explain stage by stage how geographical isolation can lead to the formation of a new species, and state what you would test in the two groups labelled ? to know if they are already distinct species.

Define biodiversity and name its three levels, providing an example of each.

Distinguish between population and community with an example from the same place: all the sparrows in a park versus all the living things in that park. Why does the concept of species apply to populations and not to communities?

In a beetle population, there are individuals with lighter and darker shells, and predators spot the lighter ones more easily against dark tree bark. Explain step by step how natural selection will act on the frequency of each colour in subsequent generations.

A horse and a donkey can interbreed and produce a mule, but they belong to different species. Explain, applying the biological species concept, why the mule does not "unite" the two species.

Distinguish between geographical isolation and reproductive isolation, and explain why reproductive isolation marks the point at which two populations have become different species.

A patient diagnosed with a bacterial infection stops an antibiotic treatment prescribed for 10 days after only 4 days because they no longer have symptoms. Two weeks later, the infection recurs more aggressively, and the same antibiotic proves ineffective. Their relative claims: "The bacteria got used to the medication in order to survive and have now become immune." Refute their relative's claim based on the theory of natural selection and reasonably predict how the frequencies of sensitive and resistant bacteria in the bacterial population will have changed between the start of the treatment, day 4, and the relapse.

On opposite sides of the Grand Canyon, there are squirrel species that are very similar yet distinct. Explain what type of speciation this example illustrates and reconstruct the process that caused it.

On an oceanic island newly formed after an eruption, a storm washes up a small raft of vegetation carrying 8 beetles of a mainland species (6 green and 2 brown). On the mainland, millions of these beetles live, where 95 % are camouflaged brown and only 5 % are green, as birds easily prey on the green ones. After several generations on the island (where there are no predatory birds), 75 % of the beetles are green. Justify which evolutionary mechanism accounts for the initial difference and predict how genetic drift will influence the population compared to natural selection if the island population remains small.

The natural fossil extinction rate ("background extinction") is estimated at 1 species per million species per year, whereas the current rate due to human activity is 100 to 1 000 times higher. Knowing that after the great mass extinctions of the past (such as the Permian or Cretaceous extinctions) the biosphere took between 5 and 10 million years to recover its biodiversity through adaptive radiation, analyze and justify why the current pace of habitat destruction cannot be buffered by the emergence of new species and what impact this will have on a geological scale on the tree of life.