Speciation and evolution

Question 1

Define speciation.

Answer 1

Any process that gives rise to a new species.

Question 2

What are some contributing factors for speciation to occur?

Answer 2

Physical separation, natural selection and evolution.

Question 3

How does speciation occur?

Answer 3

When a single population of individuals become isolated (e.g., a geographical barrier such as a water body, desert or mountain).

Question 4

What causes different natural selection pressures? (relating to speciation)

Answer 4

If the environmental conditions for the separated populations are different.

Question 5

What is the effect of different selection pressures on geographically isolated populations?

Answer 5

Different features would then be selected in each population, and any beneficial mutations that occurred in one population would not be shared with the other as there is no gene flow between the two groups.

Question 6

Summarise the process of speciation.

Answer 6

Individuals in a population become geographically isoated > no gene flow between the groups > different natural selective pressures placed on each sub-population (different environmental conditions) > over generations, populations evolve to become genetically different > two species evolve from one ancestral species.

Question 7

Define allopatric speciation.

Answer 7

The process of forming new species populations from populations separated by geographical barriers. Geographical isolation by itself does not cause speciation, there needs to be a change in the gene pool.

Question 8

Define sympatric speciation.

Answer 8

The formation of two new species from a common ancestor living in the same geographical area. This is more common in plants and bacteria, often due to polyploidy or hybridisation.

Question 9

Define convergent evolution.

Answer 9

Refers to two populations that resemble each other but are unrelated.

Question 10

Why does convergent evolution occur?

Answer 10

These different species are able to survive similar selection pressures.

Question 11

Define divergent evolution.

Answer 11

The slow and gradual accumulation of new characteristics, culminating in new species.

Question 12

Define adaptive radiation.

Answer 12

A form of divergent evolution where there is a ‘sudden emergence’ of a new species from a common ancestor. THis is typically due to a change in enviornment and differing selection pressures (such as food sources, predators and environmental conditions).

Question 13

Define succession.

Answer 13

The change in community that occurs over time.

Question 14

Define primary succession.

Answer 14

The creation of a community in an environment where there has not previously been one (e.g., in a sand dune, a rocky environment or new volcanic island).

Question 15

What are the first organisms to enter a habitat called?

Answer 15

Colonisers or pioneers; they are able to cope with unfavourable conditions.

Question 16

What are the usual pioneers?

Answer 16

Lower life forms such as lichen, creating microclimates that retain water and dust particles.

Question 17

How does soil formation occur?

Answer 17

The creation of microclimates by pioneers. Primary production (biomass created by the producers) in the community increases over time, as does species diversity, creating more complex food webs.

Question 18

Summarise the progression of primary succession.

Answer 18

Pioneer stages [bare rock > lichens > small annual plants, lichens > perennial herbs, grasses] > Intermediate stages [grasses, shrubs, shade-intolerant trees] > Climax community [shade-tolerant trees]

Question 19

Define secondary succession.

Answer 19

The change in an established community which occurs after a major environmental event such as a bush fire, flood or landslides. The event destroys or damages established species in the stable climax community, but leave behind soil rather than rock.

Question 20

What is the main difference in time between primary and secondary succession?

Answer 20

Secondary succession occurs over a much shorter time period than primary succession.

Question 21

What is the effect of reduced diversity?

Answer 21

Species with a reduced gene pool have a higher risk of becoming extinct due to a greater susceptibility to environmental pressures.

Question 22

Describe the bottleneck effect.

Answer 22

Refers to the loss of alleles due to an event where only some members of the population survive, resulting in genetic drift.

Question 23

Define the founder effect.

Answer 23

Results from a small number of individuals from a population establishing a new population - the new population may have much less genetic diversity.