Chapter 14
Practice Problems
14.1 We saw in Section 14.1 that the multilocus genotypes of individuals can be considered as
“tags” that occur in all individuals and are permanent. Palsbøll et al. (1997) used a markrecapture approach with genotypes at six microsatellite loci to estimate the number of humpback
whales in the North Atlantic Ocean. Per Palsbøll has generously provided a subset of their data
that is available in an Excel file (humpback genotypes) on the course web page. The first two
columns give the identification number and sex of each sample; identification numbers that
begin with 92XXXX were sampled in 1992, and numbers that begin with 93XXXX were
sampled in 1993. The two alleles present at the six loci (A-F) are listed in the next 12 columns.
For example, the two alleles present in each whale at locus are in the A_1 and A_2 columns.
Use these data with expression 14.2 to estimate the number of female and male humpback
whales in the North Atlantic Ocean.
14.2 We saw in Section 14.4.2 that sex is determined in Hymenoptera (bees, ants, and wasps)
by genotypes at one or more hypervariable loci. Heterozygotes at the sex-determining locus or
loci are female, and the hemizygous haploids or homozygous diploid individuals are male. At
equilibrium, all alleles at this type of a sex-determining locus are expected to be equally
frequent; that is, if there are A alleles, then each allele is expected to be at a frequency of 1/A.
What proportion of diploids is expected to be males in a population with 20 alleles at
equilibrium? What increase in diploid males is expected if a bottleneck reduces the number of
alleles to 10 or 5?
14.3 Wolves were hunted and poisoned to extinction in Sweden and Norway by the mid-20th
Century. Three wolves migrated from Russia and founded a new Scandinavian wolf population
in the early 1980s. That population now consists of approximately 100 animals. How large do
you think the Scandinavian wolf population should be to maintain genetic variation that may be
important for the viability (continued persistence) and continued evolution of this population?
There is some possibility of gene flow into this population from Russian wolves. Do you think
that it is important that gene flow between the Scandinavian and the Russian populations be
maintained in the future? Why?
14.4 What do you think is an appropriate time frame for evaluating population viability? 100
years? 1,000 years? (See Table 14.1)
14.5 Do you think the time frame for evaluating population viability should be in units of years
or generations? Why? (See Table 14.1)
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Assignment Problems
14.6 Coster et al. (2011) estimated the population size of black bears at two study sites in New
Hampshire (Pittsburg and Milan) using genetic mark-recapture with 6 highly polymorphic
microsatellite loci. A total of 57 and 65 unique genotypes were detected in Pittsburg in 2006 and
2007; 28 of the 65 unique genotypes detected in 2007 were also detected in 2006. A total of 66
and 68 unique genotypes were detected in Pittsburg in 2006 and 2007; 34 of the 68 unique
genotypes detected in 2007 were also detected in 2006. Using Expression 14.2, what is the
estimated population size at these two locations?
14.7 The Sonoran pronghorn is one of five subspecies of pronghorn (see Example 14.2). The
Sonoran subspecies is restricted to approximately 44,000 hectares in southwestern Arizona.
There were approximately 200 individuals in this population based on census estimates in the
1990s. A group of 22 biologists from a variety of federal, state, tribal, university, and
environmental organizations convened a population viability analysis (PVA) workshop in
September 1996.
Estimates of the life history parameters used by VORTEX were provided by participants of the
workshop. Some of the values were available from field data, but there were no quantitative data
available for many parameters. For these parameters, the field biologists provided “best
guesses”. The participants performed a sensitivity analysis to evaluate the response of the
simulated populations to uncertainty by varying eight parameters: inbreeding depression,
fecundity, fawn survival, adult survival, effects of catastrophes, harvest for research purposes,
carrying capacity, and size and sex/age structure of the initial population .
(a) Figure 14.10 shows the results of PVA on the Sonoran pronghorn. Based on these results,
which factors that were considered at the workshop (e.g., fecundity, adult survival, etc.) are
expected to have the greatest influence on the projected population performance? Briefly
explain the basis for your answer.
(b) A severe drought in 2002 nearly caused the extinction of this subspecies. Eighty percent of
the population was lost, from an estimated 100 animals down to a low of 21. There is concern
that this bottleneck may have caused substantial loss of genetic variation so that this population
may no longer be viable. Some have suggested that “genetic rescue” may now be appropriate.
That is, animals from other subspecies should be introduced into the Sonoran subspecies.
Do you think that introducing pronghorn from another subspecies is a good idea? Discuss the
potential advantages and disadvantages of this management action. Your specific
recommendation is less important than whether or not you consider and discuss the most
important issues involved.
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14.8 Section 14.8 discusses how large populations should be in order to be viable in the longterm. The suggestions for the effective sizes needed to retain evolutionary potential range
from 500 to 5000. The senior author once received an email with the following statements:
“As a working conservationist, I know that the dismal truth in the world is that the populations
of nearly all keystone vertebrates have been rapidly declining, and are now in the hundreds or
low thousands (census size, not effective size). Therefore, to advise that much larger numbers
are needed to prevent extinction would cause much despair among these conservationists, and
give new ammo to the nature-haters: "See, conservationists are ignoring the best science.”
This email suggests that geneticists should not recommend that the effective size of populations
need to be in the thousands in order to prevent extinction because this goal would be difficult to
reach for many species, and would, therefore, discourage conservation efforts.
Do you agree or disagree with the sentiments of this email?
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