1). Prezygotic isolating mechanisms include all of the following except
a). hybrid sterility.
b). courtship rituals.
c). habitat separation.
d). seasonal reproduction.
2). Which of the following is an example of mechanical isolation?
a). Two species of birds live in the same habitat; one mates in spring and the other in summer.
b). Two species of frogs have different mating calls.
c). The flower structure of one species prevents the transfer of pollen from another species.
d). One species of lizards inhabits the trees, and another species inhabits the ground cover.
3). __________________ isolating mechanisms include improper development of hybrids and failure of hybrids to become established in nature.
4). Reproductive isolation and the evolution of species could occur through which of the following?
a). founder effect
d). all of these
5). Speciation occurs most frequently in populations that are
b). undergoing disruptive selection.
d). not geographically separated.
6). The large number of Hawaiian Drosophila species has likely resulted from
a). adaptive radiation.
b). a single common ancestor.
c). geographic isolation.
d). all of these
7). The finch species of the Galápagos Islands are grouped according to their food sources; which of the following is not a finch food source?
d). tree buds
8). Cichlid diversity can be attributed to
a). adaptive radiation.
b). new habitats and geographic isolation.
c). a second set of jaws in the throat of the fish.
d). All of the above contributed to cichlid diversity.
9). The hypothesis that evolution occurs in spurts, with great amounts of evolutionary change followed by periods of stasis, is
a). punctuated equilibrium.
b). allopatric speciation.
d). Hardy–Weinberg equilibrium.
10). Biological diversity through time has
a). gradually increased.
b). been constant.
c). increased overall despite periodic drops.
d). both increased and decreased with no overall change.
Test Your Visual Understanding
1). In all of the examples in the figure, one interbreeding population has been divided, which results in two or more geographically isolated populations. Over time, these isolated populations can undergo little or no evolutionary change, can undergo speciation, or can become extinct. Explain under what conditions each scenario can occur:
a). Population undergoes little or no evolutionary change.
b). Population undergoes speciation.
c). Population becomes extinct.
1a). The populations that become geographically isolated may not necessarily undergo speciation. If there is no significant change in the environmental conditions to which each population is exposed, there will be no selection pressure driving evolutionary change. Except for random mutations, there may not be a change in the gene pools of these populations and unless the mutations are selected for, they will not become significant sources of variation in the populations.
1b). Allopatric divergence is the primary means of speciation. Populations that are geographically isolated often experience different environmental conditions that select for different phenotypes in the two populations. As selection and reproductive isolation increases in the two populations, speciation can result.
1c). When a population becomes divided, it is possible that the newly formed sub-populations have more limited gene pools than the parent population and have less genetic variability. Genetic drift becomes a significant factor in these populations. If the environmental conditions remain stable, these populations may survive but if the populations are exposed to shifting environmental conditions and they don't have the genetic variability in the population to response to selection pressures, the populations could become extinct.
Applying Your Knowledge
1). Adaptive radiation results when an ancestral species gives rise to many descendants which are adapted to many different parts of the environment. How would scenarios for adaptive radiation differ if speciation occurred allopatrically versus sympatrically?
Answer: Adaptive radiation results when an ancestral species gives rise to many descendants, which are adapted to many different parts of the environment. How would scenarios for adaptive radiation differ if speciation occurred allopatrically versus sympatrically?
Allopatric speciation results when descendants are separated geographically and are not able to interbreed. Under these circumstances, the two populations experience different selection pressures and can evolve into two separate species through reproductive isolation.
Sympatric speciation results when descendants remain in the same area where selective pressures would presumably be the same for all descendants. However, speciation can occur in this type of population if some descendants are barred from interbreeding because of genetic incompatibility, such as polyploidy. This can result from an error in meiosis or as a result of hybridization. Sympatric speciation, when it occurs, is usually more immediate than allopatric speciation, where the new species forms within one or two generations.
2). Polyploid animals are far less common than polyploid plants. Why do you think this might be so?
Answer: Plants contain "male" and "female" structures but very few plant species contain individuals of opposite sexes. Many animal species, on the other hand, contain male and female individuals that are determined by sex chromosomes. Animals are less viable under conditions of polyploidy because the doubling of the chromosomes, including the sex chromosome, can be very damaging and in most cases lethal. Plants can be viable with twice the number of chromosomes but the viability of animal cells is influenced by a genetic balance in the cells. Too many chromosomes can be just as damaging as too few chromosomes.