10.4.1 Speciation: What Is a Species?

Question 1

species

Answer 1

• The notion of a species can be hard to define because it is a population-level phenomenon, and populations are complex and constantly changing.
• Five working definitions of species are:
1. biological species concept
2. morphological species concept
3. recognition species concept
4. cohesion species concept
5. ecological species concept
• The above five concepts all share the common theme of genetic isolation

Question 2

Question: What is a species?

Answer 2

• In the process of constructing the definition of species, many biologists believe that genetic isolation is the most important aspect of the species concept.

Question 3

Biological species concept

Answer 3

• Two organisms are in the same species when they can produce fertile, viable offspring in free-ranging conditions. This concept emphasizes reproductive isolation. If the population of birds on the left meets these conditions, the individuals are considered members of the same species.
• A limitation of the concept is that is does not work for
  classifying extinct or asexually reproducing species.

Question 4

Morphological species concept

Answer 4

• Species are classified based upon anatomical differences. Most species that have been classified to date have been categorized by this method, especially extinct species. Reconstructing the history of human evolution largely depends on attempting to classify
  the fossil remains of the lineage. The skulls on the left are examples of individuals from different species in human evolution.
• A limitation of the concept is that is assumes that
  morphological differences are the result of substantial genetic differences between individuals

Question 5

Recognition species concept

Answer 5

• Species are classified based upon their courtship rituals (genetic, morphological, and behavioral) and mate selection. A common characteristic of a mating ritual involves the male presenting the female with
  a preferred food item. Because the two birds on the left have distinct diet preferences, the courtship ritual would be unsuccessful. The two birds are considered to be separate species.
• A limitation of this concept is that it does not work for
  classifying extinct or asexually reproducing species

Question 6

Cohesion species concept

Answer 6

• Species are classified based upon the mechanisms they use to maintain the phenotypic integrity of the population. One example is reproductive barriers.
• The graph on the left depicts a population that has undergone stabilizing selection. Stabilizing selection is a type of natural selection in which intermediate phenotypes are selected for, and extremes are selected against. Note that the curve of the evolved population is narrower than that of the original population. If a species undergoes a stabilizing selection, all of the organisms that fall within the phenotypic average will remain a member of that species.
• The advantage of this definition is that it recognizes the occurrence of fertile hybrids produced by the interbreeding of two different species while acknowledging the integrity of the parent species. For example, dogs and coyotes may interbreed in the wild and produce offspring. In a zoo setting, lions and tigers may mate and produce offspring. Under the cohesion species concept, each of the four is considered as a
  separate species.
• A limitation of this concept is that it does not work for
  classifying extinct species.

Question 7

Ecological species concept

Answer 7

• Species are classified based on their ecological niche or role in the environment. An ecological niche is all of an organism’s adaptations, its use of resources, and the life history that it has in its community. The two fish in ponds A and B, respectively, are geographically isolated but share a similar ecological niche in terms of diet and life history. According to the ecological species concept, the two are considered to be members of the same species.
• A limitation of this concept is that the ecological niche
  encompasses a vast array of details involving the life history of an organism—some of which may be difficult to observe in nature and may be completely lacking in the fossil record.

Question 8

Which of the following statements best describes the biological species concept?

Answer 8

• reproductively isolated

Question 9

What is a problem with using the morphological species concept to compare organisms in the fossil record?

Answer 9

• Morphological differences do not necessarily indicate genetic differences.

Question 10

What is a species?

Answer 10

• Species is difficult to define because it is a population-based phenomenon, and populations are complex and constantly changng.

Question 11

A prezygotic barrier

Answer 11

• prevents union of the egg and sperm.

Question 12

The __________ concentrates on mechanisms that maintain species as discrete phenotypic entities.

Answer 12

• cohesion species concept

Question 13

What is the ecological species concept based upon?

Answer 13

• what an animal does and how it lives