Chapter 24: The origin of species(1)

Question 1

Define speciation.

Answer 1

Speciation is the process by which one species splits into two or more species

Question 2

What did speciation explain?

Answer 2

Unity and Diversity of Life

1. Speciation fascinated Darwin (and many biologists since) because it has produced
   a tremendous diversity of life, repeatedly yielding new species that differ from existing ones.
2. Later, Darwin realized that speciation also helps to explain the many features
   that organisms share (the unity of life)

Question 3

Differentiate between microevolution and macroevolution.

Answer 3

Microevolution is changes over time in allele frequencies in a population.

Macroevolution is the broad pattern of evolution above the species level.

Question 4

What does evolutionary theory explain?

Answer 4

Evolutionary theory explains how

– new species originate and
– populations evolve

Question 5

When comparing organisms, What do biologists look for?

Answer 5

When grouping organisms, Biologists compare:

– morphology
– physiology
– biochemistry and
– DNA sequences in organisms

Question 6

How does the biological species concept define species?

Answer 6

A species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring—but do not produce viable, fertile offspring with members of other such groups.

Question 7

The biological species concept is based on the potential to _______ rather than on _______.

Answer 7

The biological species concept is based on the potential to interbreed rather than on physical similarity.

Question 8

Define reproductive isolation.

Answer 8

Reproductive isolation is the existence of biological factors (barriers) that prevent two species from producing viable, fertile offspring

Question 9

How can reproductive isolation be classified?

Answer 9

Reproductive isolation can be classified by whether factors act

– before (prezygotic) fertilization or
– after fertilization (postzygotic

Question 10

How do pre-zygotic barriers work?

Answer 10

Prezygotic barriers block fertilization from occurring by:

– impeding different species from attempting to mate
– preventing the successful completion of mating
– hindering fertilization if mating is successful

Question 11

Name the pre-zygotic barriers.

Answer 11

• Habitat Isolation
• Temporal Isolation
• Behavioural Isolation
• Mechanical Isolation

Question 12

Differentiate between habitat and temporal isolation with examples.

Answer 12

Habitat isolation: Two species that occupy different habitats within the same area may encounter each other rarely, if at all, even though obvious physical barriers, such as mountain ranges isolate them.

Temporal isolation: Species that breed during
different times of the day, seasons, or years cannot mix their gametes.

Question 13

Differentiate between mechanical and behavioral isolation.

Answer 13

Behavioral isolation: Courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers, even between closely related species.

Mechanical isolation: Mating is attempted, but morphological differences prevent its successful completion.

Question 14

Name the post-zygotic barriers.

Answer 14

• Gametic Isolation
• Reduced Hybrid Viability
• Reduced Hybrid Fertility
• Hybrid Breakdown

Question 15

Differentiate between gametic isolation and hybrid breakdown.

Answer 15

Gametic isolation: The sperm of one species may not be able to fertilize the eggs of
another species.

Hybrid breakdown: Some first-generation hybrids are viable and fertile, but when
they mate with one another or with either parent species, offspring of the next generation are feeble or sterile

Question 16

Differentiate between Reduced Hybrid and Viability Reduced Hybrid Fertility

Answer 16

1. Reduced hybrid viability: The genes of different parent species may interact in ways that impair the hybrid’s development or survival in its environment.
2. Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile.

Question 17

What are the limitations of the biological species concept?

Answer 17

• The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes)
• The biological species concept emphasizes the absence of gene flow. Gene flow can occur between distinct species(Ex, Grizzly bears and polar bears can mate to produce
  “grolar bears”)

Question 18

How does the morphological concept define species?

Answer 18

The morphological species concept characterizes a species by body shape and other structural features and suggests that each species is morphologically distinct.

Question 19

What is the strength of the biological species concept?

Answer 19

One strength of the biological species concept is that it directs our attention to a way by which speciation can occur: by the evolution of reproductive isolation

Question 20

What are the advantages of the morphological species concept?

Answer 20

The morphological species concept can be

• Applied to asexual and sexual organisms
• It can be useful even without information on the extent of gene flow.

Question 21

What is the disadvantage of the morphological species concept?

Answer 21

One disadvantage, however, is that this definition relies on subjective criteria; researchers may disagree on which structural features distinguish a species.