MODES OF SPECIAT

ION

MODES OF SPECIATION

There are different modes that can lead to the formation of new species:

Sympatric and Allopatric speciation

SYMPATRIC SPECIATIONA single population divides suddenly into two

reproductively isolated groups within the same geographical area.

Plants are best example – due to changes in chromosome number (polyploidy) doubling of chromosome number during cell division.

These plants can no longer breed with the plants around them.

SYMPATRIC SPECIATION

Many plants are able to reproduce both sexually and asexually. If an individual plant has a mutation that prevents successful sexual reproduction, it may beable to reproduce asexually.

ALLOPATRIC SPECIATIONNew species are formed once

populations are physically separated. Once separated, they can no longer exchange genetic information. Over generations the two population become less and less alike. Any mutations that arise in one population are not shared with the other population. Different environments lead to different forms of natural selection.

ALLOPATRIC SPECIATION

PACE OF SPECIATIONPhyletic gradualismChange is very slow but steady within a

lineage before or after a divergence (splitting of a line of descent)

Could explain the lack of transitional species, because the changes are subtle

PACE OF SPECIATIONPunctuated equilibriumSpeciation occurs rapidly during

periods of stasis (limited change)

This could also explain the lack of transitional species, because the changes are significant

IS SPECIATION SMOOTH OR JERKY?Gradualism model Punctuated equilibrium

model