The Origin of Species

Page
3

PostZygotic Reproductive Barrier

Mule: sterile hybrid offspring between horse and donkey

Slide 17

Other Definitions of Species

The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes).

Other species concepts emphasize the unity within a species rather than the separateness of different species.

The morphological species concept defines a species by structural features.

It applies to sexual and asexual species but relies on subjective criteria.

Slide 18

The ecological species concept views a species in terms of its ecological niche.

It applies to sexual and asexual species and emphasizes the role of disruptive selection.

The phylogenetic species concept: defines a species as the smallest group of individuals on a phylogenetic tree.

It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species.

Slide 19

Concept 24.2: Speciation can take place with or without geographic separation

Speciation can occur in two ways:

Allopatric speciation: geographic barrier separates populations.

Sympatric speciation: no geographic barrier

Slide 20

Speciation

(a) Allopatric speciation

(b) Sympatric speciation

Slide 21

Allopatric (“Other Country”) Speciation

In allopatric speciation, gene flow is interrupted or macroevolution is the cumulative effect of many speciation and extinction events.

reduced when a population is divided into geographically isolated subpopulations … A geographic barrier separates the original population.

Separate populations may evolve independently through mutation, natural selection, and genetic drift.

Reproductive isolation between populations generally increases as the distance between them increases.

Barriers to reproduction are intrinsic; separation itself is not a biological barrier.

Slide 22

Allopatric Speciation

A. harrisi

A. leucurus

Slide 23

Continental Drift Caused Allopatric Speciation

Mantellinae

(Madagascar only):

100 species

Rhacophorinae

(India/Southeast

Asia): 310 species

Other Indian/

Southeast Asian

frogs

Millions of years ago (mya)

1

2

3

1

2

3

100

80

60

40

20