Chapter 20
Practice Problems
20.1 We saw in Chapters 6 and 15 that the loss of genetic variation caused by population
bottlenecks is harmful. Introduced species generally go through a founding population
bottleneck. Why are introduced species often so successful if population bottlenecks are
harmful?
20.2 We saw in Chapters 8 and 16 that local adaptation is an important concern for conservation.
Invasive species that have not had the opportunity to develop local adaptations often replace
native species that we would expect to be locally adapted. Why?
20.3 Assume there are two conspecific populations that each have an average heterozygosity
(HS) of 0.10. These two populations are moderately genetically diverged from each other
(FST=0.20). What would be the average heterozygosity in a new population that is founded by a
large number of founders from each of these populations? Assume an equal number of founders
are derived from each population.
20.4 How much gene flow do you think is needed before two geographically isolated
populations should be considered the same “unit of eradication”?
20.5 According to standards set by the International Plant Protection Convention, imports
cannot be restricted for species that are already widespread and are not the object of an “official”
control program. Do you think that this policy is biologically sound? Why or why not?
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Assignment Problems
20.6 A symposium in 1964 brought together a collection of the world’s best population and
evolutionary biologist to discuss the genetics of colonizing and invasive species (Baker and
Stebbins 1965). The following exchange took place between R.C. Lewontin and Ernst Mayr (p.
481):
Lewontin: I would like to be a spokesman for the geneticists and clear up the confusion that I
think we’ve spread about the effect of small numbers in colonizations. If there is colonization by
a single fertilized female, there will be a loss of genes and a radical change in gene frequencies at
loci where alleles are at intermediate frequencies. But the one thing that will not happen is a
profound change in the total amount of genetic variation available.
Mayr: But isn’t that based on certain assumptions? Suppose you had a thousand loci each with
25 isoalleles, are you still telling us that you get 75% of that variation in that one single pregnant
female?
How do you think Lewontin replied? Who’s correct?
20.7 Rainbow trout are considered one of the world’s top 100 harmful invasive species (Global
Invasive Species Database, http://www.issg.org/database/species/search.asp?st=100ss). Rainbow
trout were introduced into the waters of Chile in the late 1800s, and they have had a devastating
effect on the native fish fauna of Chile (Gajardo and Laikre 2003). Rainbow trout also provide a
valuable sport fishery in Chile, and there have been some efforts to consider rainbow trout
“naturalized” and treated as if they were native rather than as a threat to the natural biota.
When do you think rainbow trout should be considered as “naturalized” in Chile?
20.8 Feral cats in Australia have had a devastating effect on the native fauna (Dickman 1996).
There have been many reports that feral cats in Australia are exceptionally large. Cats were
introduced to Australia in the 1800s. It is not known whether the apparent large size of feral cats
in Australia has a genetic basis. Design a program that would allow you to test whether the large
size of feral cats is has a genetic or environmental basis.
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