21) Species A is divided by a newly formed river to become two populations. These populations diverge to become two different species, B and C. If the river is dammed upstream, eliminating an isolating mechanism between B and C, what will happen?

A) Gene flow will resume.

B) Species B and C will be considered subspecies.

C) Species B and C will remain genetically isolated.

D) Species will unite to form a hybrid species, D.

22) ________ isolating mechanisms are outside factors that prevent interbreeding.

A) Intrinsic

B) Extrinsic

C) Behavioral

D) Mechanical

23) Horses and donkeys mate successfully to produce mules, which are always sterile. Which genetic isolating mechanism is involved here to prevent horses and donkeys from becoming a single species?

A) hybrid infertility

B) behavioral isolation

C) mechanical isolation

D) gametic isolation

24) Blue-footed boobies of the Galapagos will mate only after a very specific courtship display on the part of the male. He high-steps to advertise his bright blue feet. What isolating mechanism discourages mating outside the species?

A) temporal isolation

B) ecological isolation

C) gametic isolation

D) behavioral isolation

25) Two species of garter snakes live in the same geographic area. One mainly lives in water, and the other mainly on land, so they rarely encounter each other and do not interbreed. This is an example of what type of isolating mechanism?

A) directional

B) temporal

C) mechanical

D) ecological

26) Two species of pines, Pinus radiata and Pinus muricota, live together in California and are capable of forming hybrids under laboratory conditions. However, they do not interbreed because one releases pollen in February and the other in April. What is the genetic isolating mechanism involved?

A) gametic

B) ecological

C) geographic

D) temporal

27) In order for allopatric speciation to occur, first there must be a geographic separation of two populations of the same species. The second step requires:

A) additional extrinsic isolating mechanisms to become involved.

B) an increase in gene flow between the populations.

C) physical and behavioral changes that keep them from interbreeding.

D) physical and behavioral changes that permit occasional hybridization.

28) There are currently many similar but different species on either side of the isthmus of Panama. They probably resulted from:

A) large rapid changes in their gene frequencies.

B) hybridization.

C) sympatric speciation.

D) allopatric speciation.

29) In many species of fireflies, males flash to attract females. Each species has a different flashing pattern. This is an example of:

A) behavioral isolation.

B) allopatric speciation.

C) geographic isolation.

D) natural selection.

30) Eastern and western meadowlarks look almost identical and sometimes inhabit the same areas of prairies. They recognize members of their own species by distinctive songs and thus do not breed with each other. This is an example of:

A) geographic isolation.

B) ecological isolation.

C) no isolation mechanism.

D) behavioral isolation.