NCEA Level 3 Biology - Speciation

Evolution

The permanent genetic change (change in allele frequencies) in a population of individuals over time

population

Members of a species that live in the same geographical area and share a common gene pool.

Deme

A local population that has no or limited gene flow with members of other populations. Local natural selection pressures mean that the phenotypic features of the members of one population may differ from those of members of others.

Cline

When a species has an extended geographical range, variation may occur along a gradient from one point of the range to another point.

Gene flow

Movement of alleles carried by individuals between populations; an important source of genetic variation upon which natural selection can then act.

Genetic drift

The random change in allele frequencies of a population due to chance events.

Bottleneck effect

Catastrophic environmental events (fire, drought, floods, earthquakes etc) or human impact (habitat destruction, introduction of predators or competitors) can severely reduce a population size to just a small number of survivors.

Founder effect

Occurs when only a few individuals from a population move into a new area. They may not possess a representative sample of the available genes from that species' gene pool.

Inbreeding

Breeding between closely related individuals.

Natural selection

The process by which beneficial phenotypes in a population are preserved because they are selected for while unfavourable phenotypes tend to be lost because they are selected against.

Types of natural selection

- Stabilising
- Directional
- Disruptive

Stabilising natural selection

Favours the average phenotype and selects against both extremes.

Directional natural selection

Favours one extreme phenotype over the others.

Disruptive natural selection

Favours both extreme phenotypes at the expense of the average.

Mutation

Permanent change in the DNA in a gene or chromosome; ultimate source of variation.

Speciation

Formation of new species. It results from populations becoming reproductively isolated so gene flow can no longer occur.

Sympatric species

Closely related species that live in the same geographic location

Allopatric species

Closely related species that live in different geographic locations

Reproductive isolating mechanism

Any factor that stops members of populations of the same species or members of different species from breeding together; it acts as a barrier to gene flow. May be prezygotic or postzygotic.

Prezygotic isolating mechanisms

These include:
- Geographical isolation
- Structural (morphological) isolation
- Ecological isolation
- Temporal isolation
- Behavioural isolation
- Gametic isolation

Geographical isolation

Results from physical barriers (e.g. rivers, mountain ranges, oceans) separating populations.

Structural (morphological) isolation

Results from differences between the structure of external reproductive organs (genitalia) that do not allow for transfer of sperm between the sexes.

Ecological isolation

Results from differences in habitat within the same geographical area

Temporal isolation

Results from breeding behaviour resulting at different, non-overlapping times.

Behavioural isolation

Results from differences in behaviour, typically mating behaviour such as courtship.

Gametic isolation

Results from incompatibility of gametes.

Hybrid inviability

The zygote, embryo or offspring is inviable (i.e. unable to survive or develop normally), so dies early in its development.

Hybrid sterility

The hybrid reaches maturity but is infertile so cannot breed.

Hybrid breakdown

Occurs when the hybrid reaches maturity and is able to breed but the next or subsequent generations are infertile or have reduced reproductive capability.