Populations of some kinds of organisms may be isolated by a barrier as small as a roadway, while other organisms require a much larger physical barrier to block gene flow. What features of organisms might determine how readily they become geographically isolated? What impact might these features have on how often or how rapidly speciation is likely to occur in these groups?

In allopatric spéciation (select all that apply):

a. allele frequency changes are shared between populations of the same species.

b. populations are geographically isolated.

c. gene flow between populations is greatly reduced because of geographic separation

d. populations accumulate genetic changes over time that result in physical or behavioral changes that eventually block successful interbreeding.

e. populations are directly adjacent.

In an adaptive radiation, one species may colonize a previously empty environment, such as an island, and diversify evolutionarily into a set of closely related species that occupy a very wide range of habitats. For example, with Darwin’s finches on the Galapagos Islands, one species fills the role of woodpecker by using a stick to tap on trees and dig out insects. Do you think that such a species would have been likely to evolve in an area that already had woodpeckers? Why or why not?

Possible intrinsic reproductive isolating mechanisms include (select all that apply):

a. mating at different times of year or times of day.

b. geographical isolation.

c. incompatibility between eggs and sperm that prevent fertilization.

d. singing a different mating song than another species.

e. producing fertile hybrids.

In ocean-dwelling creatures such as sea urchins or corals, sperm and eggs are released into the water by males and females and fertilization occurs externally. If several closely related species of coral live in the same location, what reproductive isolating mechanisms could potentially prevent interbreeding? (Select all that apply.)

a. behavioral isolation

b. gametic isolation

c. temporal isolation

d. ecological isolation

e. hybrid infertility

Order the following categories into the appropriate biological hierarchy, with the least inclusive category first

a. family

b. species

c. phylum

d. genus

e. class

Factors that can be problems in determining relatedness among organisms may include (select all that apply):

a. homologous traits.

b. analogous traits.

c. convergent evolution.

d. poor fossil record.

e. shared derived traits.

Adaptive radiations (select all that apply):

a. can be seen most clearly in mainland environments.

b. are episodes of rapid speciation that occur when the “fit” between environment and species is in flux.

c. concern the evolution of heat loss in vertebrates experiencing stressful climates.

d. are exemplified by the Hawaiian drosophilid flies.

e. can be seen most clearly in island environments.

True or false: If an insect has 1,000 offspring, we can label it as “fit” in an evolutionary sense.

In stabilizing selection, forms that are _______ are favored over forms that are_______.