2- natural selection and evolution

What is the niche of a species?

Its role within its ecosystem/ habitat. Species which share the same niche compete with each other and the better adapted species will survive.

Organisms are adapted to their environment in various ways including:

• Anatomical adaptations- physical adaptions, either external or internal e.g. presence of long loops of Henle which allow desert mammals to produce concentrated urine and minimise water loss.

• Behavioural adaptations- changes in behaviour which improve the organism’s chance of survival e.g. mating calls.

• Physiological adaptations- processes involving enzymes/ hormones that increase an organism’s chance of survival e.g. regulation of blood flow through the skin.

Define natural selection.

The process in which fitter individuals who are better adapted to the environment are more likely to survive and reproduce and pass on the advantageous alleles to their offspring.

Define evolution.

The process by which the frequency of alleles in a gene pool changes over time as a result of natural selection.

What are the steps for evolution to occur via natural selection.

• A variety of phenotypes exist within a population due to mutations.

• An environmental change occurs and as a result of that, the selection pressure changes.

• Some individuals possess advantageous alleles which give them a selective advantage and allow them to survive and reproduce.

• The advantageous alleles are passed on to their offspring.

• Over time, the frequency of alleles in a population changes.

What is speciation?

If two populations become reproductively isolated, new species will be formed.

Due to the accumulation of different genetic information in populations over time due to different environments and selection pressures.

What are the two types of speciation that can occur and describe them.

Allopatric (where the isolation is geographic due to a river being formed due to flooding etc)

Sympatric (speciation occurs when two populations are in same environment but differences in mating, food sources, chromosomal pattern changes e.g. polyploidy etc.)