Chapter 24: The origin of species(2)

Question 1

How does the ecological concept define species?

Answer 1

The ecological species concept views a species in terms of its ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment.

Question 2

What are the advantages of the ecological species concept?

Answer 2

– It applies to sexual and asexual species
- Emphasizes the role of disruptive selection

Question 3

How does the phylogenetic concept define species?

Answer 3

The phylogenetic species concept defines a species as the smallest group of individuals that share a common ancestor.

Question 4

What are the limitations and advantages of the phylogenetic species concept?

Answer 4

– It applies to sexual and asexual species

– It can be difficult to determine the degree of difference required for separate species.

Question 5

What are the two types of speciation ?

Answer 5

Allopatric speciation and Sympatric speciation

Question 6

Differentiate between allopatric and sympatric speciation.

Answer 6

In allopatric speciation, groups from an ancestral population evolve into separate species due to a period of geographical separation

In sympatric speciation, speciation occurs in populations that live in the same geographic area.

Question 7

Allopatric speciation can only occur with geologic remodeling. True or false, justify.

Answer 7

False.

Allopatric speciation can also occur without geologic remodeling, as when individuals colonize a remote area and their descendants become geographically isolated from the parent population

Question 8

In allopatric speciation, how may separated populations evolve independently?

Answer 8

Separated populations may evolve independently through
– mutation
– natural selection, and
– genetic drift

• Reproductive isolation may arise as a result of genetic divergence

Question 9

How formidable must a geographic barrier be to promote allopatric speciation?

Answer 9

The answer depends on the ability of the organisms to move about.

Question 10

Define sympatric speciation.

Answer 10

In sympatric speciation (from the Greek syn, together), speciation occurs in populations that live in the same geographic area.

Question 11

How does sympatric separation occur?

Answer 11

Sympatric speciation can occur if gene flow is reduced by factors including:

– Polyploidy
– Sexual selection
– Habitat differentiation

Sympatric speciation can also result from the appearance of new ecological niches

Question 12

Define polyploidy and what is autoploid.

Answer 12

A species may originate from an accident during cell division that results in extra sets of chromosomes, a condition called polyploidy

Question 13

Differentiate between autoploidy and alloploidy.

Answer 13

An autopolyploid is an individual that has more than two chromosome sets that are all derived from a single species.

An allopolyploid is a species with multiple
sets of chromosomes derived from different species

Question 14

how does alloploidy take place?

Answer 14

When two different species interbreed and produce hybrid offspring, Most such
hybrids are sterile because the set of chromosomes from one species cannot pair during meiosis with the set of chromosomes from the other species.

However, an infertile hybrid may be able to propagate itself asexually (as many plants can do).

In subsequent generations, various mechanisms can change a sterile hybrid into a fertile polyploid called an allopolyploid

Question 15

What is a hybrid zone?

Answer 15

A hybrid zone is a region in which members of different species meet and mate, and produce hybrids

• Typically located wherever the habitats of interbreeding species meet
• Hybrids often have reduced fitness compared with parent species

Question 16

Can changes in the environment alter hybrid zones?

Answer 16

A change in environmental conditions can alter where the habitats of interbreeding species meet.

When this happens, an existing hybrid zone can move to a new location, or a novel hybrid zone may form.

Question 17

When closely related species meet in a hybrid zone, what are the 3 possible outcomes?

Answer 17

When closely related species meet in a hybrid zone, there are three possible outcomes:

– reinforcement
– fusion
– stability

Question 18

Explain reinforcement as an outcome of hybrid zones.

Answer 18

When hybrids are less fit than parent species, reinforcement of reproductive barriers may occur through strong selection for prezygotic barriers

• Over time, the rate of hybridization decreases
• Where reinforcement occurs, reproductive barriers should be stronger for sympatric than allopatric species

Question 19

Explain fusion as a result of hybrid zones over time.

Answer 19

Barriers to reproduction may be weak when two species meet in a hybrid zone. Indeed, so much gene flow may occur that
reproductive barriers weaken further and the gene pools of the two species become increasingly alike.

In effect, the speciation process reverses, eventually causing the two hybridizing species to fuse into a single species.

Question 20

Explain stability as a result of hybrid zones over time.

Answer 20

Hybrids continue to be produced, in some cases, this occurs because the hybrids survive or reproduce better than members of either parent species, at least in certain habitats or years.