Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
Chapter 14
14.1
1. Macroevolutionary events are large-scale evolutionary changes that occur over long periods of
time, while small scale microevolutionary events occur over shorter time periods.
Microevolutionary events lead to macroevolutionary events.
2. The modern definition of a species recognizes the potential for interbreeding, whereas
Linnaeus’ definition relied on external appearance alone. Linnaeus thought that each species
was specially created and that species never changed or disappeared; modern taxonomists
recognize the importance of evolution.
3. Some of the challenges in defining and describing species include:
- individuals of a species vary, and some species look quite similar;
- in captivity, some species that never encounter one another in nature will interbreed and
produce fertile offspring;
- asexually reproducing species do not conform to the biological species concept;
- reproductive isolation of species known only as fossils cannot be observed;
- some species are not absolutely reproductively isolated.
14.2
1. Reproduction is an immensely complicated process involving behavioral, biochemical, and
developmental events. Reproductive isolation can occur if any part of the process is disrupted.
For instance, species can be reproductively isolated because of different patterns of courtship, or
because of biochemical differences that isolate species at fertilization, during embryonic
development, or during growth to sexual maturity.
2. Five different modes of prezygotic reproductive isolation are:
- habitat isolation: two populations don’t share a habitat;
- temporal isolation: two populations are active at different times;
- behavioral isolation: two populations have different mating behaviors;
- mechanical isolation: the sexual organs of members of the two populations may not be
complementary;
- gametic isolation: sperm of one population may not be able to fertilize eggs of another
because of biochemical differences.
3. Postzygotic reproductive isolation can occur in two major ways:
- hybrid inviability: a hybrid embryo may die because the genes of its parents are not
compatible;
- hybrid infertility: a surviving hybrid may be sterile and unable to produce viable offspring.
14.3
1. In allopatric speciation, a geographic barrier separates two populations. One example is the
wide rivers that are a barrier to gene flow between tamarin monkey species. Parapatric speciation
occurs along a border between the ranges of two species. The intergrades of little greenbul
species in the ecotones between rain forest and grassland are an example. Sympatric speciation
occurs within the overlapping ranges of two species. The divergence of a new population of
Clarkia rubicunda following a drought, and its subsequent inability to reproduce with Clarkia
species from the surrounding area after the drought, is an example of sympatric speciation.
2. Changes in chromosome number can create a new population within the range of the original
population. The resulting reproductive isolation can lead to sympatric speciation.
3. Some difficulties in considering the effects of geography on speciation include:
- the three kinds of geographic isolation are points on a continuum rather than discrete
situations;
- humans may be unaware of the actual barriers to speciation that keep populations
separate;
-
there is no agreement over how large a geographic feature must be to qualify for status
as a geographic barrier to speciation. A feature that may be miniscule to one species
may be insurmountable to another.
14.4
1. Gradualism posits that the rate of evolutionary change is slow and steady and continuous, with
many intermediate forms. Punctuated equilibrium posits that evolutionary change occurs in
discontinuous, fast bursts that interrupt long periods in which a species does not change. Both
models can occur because of the extreme diversity of species, habits, and habitats, and because
of differences in the pace of environmental change over time.
2. Three ways that adaptive radiation can occur are:
- a few individuals colonize a new habitat; multiple species are produced as different food
sources simultaneously select for different phenotypes;
- a few individuals of a population have a new structure or ability; the environment selects
for them, and two new species evolve;
- members of a population vary in their ability to survive after a major environmental
change. After a catastrophe that wipes out many species, these survivors diversify as
they exploit the changed environment.
14.5
1. Factors that can hasten extinction restrict a population’s ability to survive environmental
change. These include small population size, restricted genetic diversity, a limited environment,
inbreeding, habitat loss, introduction of new diseases or new predators, and ecological disasters.
2. Mass extinctions occur only rarely and seem to occur periodically. They kill off many different
species over a short period of time. In contrast, background extinctions continually occur at a
steady rate of 0.1 to 1.0 species per year per million species.
3. Humans have influenced extinctions by destruction of habitats due to agriculture and
urbanization, introducing alien species that compete with native species, and overharvesting or
hunting species to extinction.
14.6
1. Tree diagrams use lines to show evolutionary history. The lines branch or fork to show
speciation and stop to show extinction.
2. DNA sequences help biologists refine phylogenies by confirming the evolutionary relationships
among species. Estimates of mutations rates also allow timescales to be added to branching
diagrams.