Chapter 24 Homework – KEY
1. Contrast and compare the morphological species concept and the biological species concept.
– Morphological species: similar in form and structure
– Biological species: ability to interbreed in nature and produce fertile offspring
2. Discuss which species concept(s) you would apply to asexual reproducing species.
– Morphological species concept can be used for asexual reproducing species since it is
impossible to know their biological interbreeding information
3. Discus which species concept would be the most useful for identifying species in the field.
– Since breeding data is often lacking while in the field, morphological species
definitions are much easier to apply.
4. For the following situations, identify if it is a pre- or postzygotic situation AND predict what
type of reproductive barrier is probably in place.
a) Two species of dragonflies emerge during different weeks in the summer pre-, temporal
b) Tree frogs breed in woodland ponds; leopard frogs breed in swamps pre-, habitat
c) Two flower species with different length nectar tubes are pollinated by different moths
pre-, mechanical
d) Two species of Streptocarpus are crossed and produced viable, but sterile offspring
post-, reduced hybrid fertility
e) Two species of coral release gametes on the same night, but no cross fertilization occurs
pre-, gametic
f) Two similar looking species of birds have different courting songs and dances
pre-, behavioral
5. Contrast and compare Allopatric and Sympatric speciation.
– Allopatric: when geographical isolation interrupts the gene flow between two
populations
– Sympatric: reproductive barriers prevent gene flow between individuals within the
same geographical location
6. Consider two species that diverged while geographically separated, but resumed contact
before reproductive isolation was complete. Predict what would happen over time if the two
species mated indiscriminately and:
a) the F1 hybrid offspring survived and reproduced as well as offspring from intraspecific
matings within each original species.
the barriers are failing to separate the two species and they may fuse together
b) the F1 hybrid offspring survived, but reproduced more poorly than the offspring from
intraspecific matings within each original species
– the barriers would continue to separate the two species.
7. According to Punctuated Equilibrium, discuss what environmental characteristics facilitate
a “punctuated “state of rapid speciation and change. Discuss what environmental
characteristics facilitate an equilibrium rate of speciation and change.
– an unstable and rapidly changing environment favors rapid speciation such as that
created by a catastrophic die-off event, or the creation of a brand new
environment where adaptive radiation can occur such as in the creation of a new island.
– equilibrium rates of speciation are most likely in very stable environments that change
only slowly.
8. Discuss why the Punctuated Equilibrium is a better model for dealing with gaps and missing
links in the fossil record.
- Punctuated equilibrium says that periods of rapid speciation are unlikely to leave the
evidence of links in the fossil record. It expects gaps to occur because the very
short time involved in the origin of the new species is too rapid for fossilization to capture.
9. Examine the Monkey flower case on page 504. Discus the role of pollinator choice in the
speciation of these plants.
– the color of the flower attracts different pollinators. If the color is changed as was
done in the experiment, the pollinator changed. This would affect how the
populations are kept isolated from each other. Usually the pollinator stays
specific to one color/population keeping the two species isolated.
10. Speciation can occur rapidly between diverging populations, yet the time between speciation
events is often a million years. Explain this apparent contradiction.
– mutations or other rapid changes can drive rapid speciation events, especially if a
developmental or control gene is mutated.
– mutations are random events. If the environment remains stable, a mutation may not
be able to cause a speciation event very rapidly, possible taking millions of years
between mutation events. The contradiction is due to the timing of mutations.